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Talha-Dean T, Tarn Y, Mukherjee S, John JW, Huang D, Verzhbitskiy IA, Venkatakrishnarao D, Das S, Lee R, Mishra A, Wang S, Ang YS, Johnson Goh KE, Lau CS. Nanoironing van der Waals Heterostructures toward Electrically Controlled Quantum Dots. ACS APPLIED MATERIALS & INTERFACES 2024; 16:31738-31746. [PMID: 38843175 DOI: 10.1021/acsami.4c03639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/22/2024]
Abstract
Assembling two-dimensional van der Waals (vdW)-layered materials into heterostructures is an exciting development that sparked the discovery of rich correlated electronic phenomena. vdW heterostructures also offer possibilities for designer device applications in areas such as optoelectronics, valley- and spintronics, and quantum technology. However, realizing the full potential of these heterostructures requires interfaces with exceptionally low disorder which is challenging to engineer. Here, we show that thermal scanning probes can be used to create pristine interfaces in vdW heterostructures. Our approach is compatible at both the material- and device levels, and monolayer WS2 transistors show up to an order of magnitude improvement in electrical performance from this technique. We also demonstrate vdW heterostructures with low interface disorder enabling the electrical formation and control of quantum dots that can be tuned from macroscopic current flow to the single-electron tunneling regime.
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Affiliation(s)
- Teymour Talha-Dean
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
- Department of Physics and Astronomy, Queen Mary University of London, London E1 4NS, U.K
| | - Yaoju Tarn
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Subhrajit Mukherjee
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - John Wellington John
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Ding Huang
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Ivan A Verzhbitskiy
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Dasari Venkatakrishnarao
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Sarthak Das
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Rainer Lee
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Abhishek Mishra
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
| | - Shuhua Wang
- Science, Mathematics and Technology, Singapore University of Technology and Design, 8 Somapah Road, Singapore 487372, Singapore
| | - Yee Sin Ang
- Science, Mathematics and Technology, Singapore University of Technology and Design, 8 Somapah Road, Singapore 487372, Singapore
| | - Kuan Eng Johnson Goh
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
| | - Chit Siong Lau
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
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2
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Singh K, Chew A, Herzog-Arbeitman J, Bernevig BA, Vafek O. Topological heavy fermions in magnetic field. Nat Commun 2024; 15:5257. [PMID: 38898060 PMCID: PMC11187166 DOI: 10.1038/s41467-024-49531-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Accepted: 06/07/2024] [Indexed: 06/21/2024] Open
Abstract
The recently introduced topological heavy fermion model (THFM) provides a means for interpreting the low-energy electronic degrees of freedom of the magic angle twisted bilayer graphene as hybridization amidst highly dispersing topological conduction and weakly dispersing localized heavy fermions. In order to understand the Landau quantization of the ensuing electronic spectrum, a generalization of THFM to include the magnetic field B is desired, but currently missing. Here we provide a systematic derivation of the THFM in B and solve the resulting model to obtain the interacting Hofstadter spectra for single particle charged excitations. While naive minimal substitution within THFM fails to correctly account for the total number of magnetic subbands within the narrow band i.e., its total Chern number, our method-based on projecting the light and heavy fermions onto the irreducible representations of the magnetic translation group- reproduces the correct total Chern number. Analytical results presented here offer an intuitive understanding of the nature of the (strongly interacting) Hofstadter bands.
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Affiliation(s)
- Keshav Singh
- National High Magnetic Field Laboratory, Tallahassee, FL, 32310, USA
- Department of Physics, Florida State University, Tallahassee, FL, 32306, USA
| | - Aaron Chew
- Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | | | - B Andrei Bernevig
- Department of Physics, Princeton University, Princeton, NJ, 08544, USA
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018, Donostia-San Sebastian, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - Oskar Vafek
- National High Magnetic Field Laboratory, Tallahassee, FL, 32310, USA.
- Department of Physics, Florida State University, Tallahassee, FL, 32306, USA.
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Zhou W, Hua J, Liu N, Ding J, Xiang H, Zhu W, Xu S. Inversion Symmetry-Broken Tetralayer Graphene Probed by Second-Harmonic Generation. NANO LETTERS 2024. [PMID: 38885205 DOI: 10.1021/acs.nanolett.4c01880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2024]
Abstract
Stacking orders provide a unique way to tune the properties of two-dimensional materials. Recently, ABCB-stacked tetralayer graphene has been predicted to possess atypical elemental ferroelectricity arising from its symmetry breaking but has been experimentally explored very little. Here, we observe pronounced nonlinear optical second-harmonic generation (SHG) in ABCB-stacked tetralayer graphene while absent in both ABAB- and ABCA-stacked allotropes. Our results provide direct evidence of symmetry breaking in ABCB-stacked tetralayer graphene. The remarkable contrast in the SHG spectra of tetralayer graphene allows straightforward identification of ABCB domains from the other two kinds of stacking order and facilitates the characterization of their crystalline orientation. The employed SHG technique serves as a convenient tool for exploring the intriguing physics and novel nonlinear optics in ABCB-stacked graphene, where spontaneous polarization and intrinsically gapped flat bands coexist. Our results establish ABCB-stacked graphene as a unique platform for studying the rare ferroelectricity in noncentrosymmetric elemental structures.
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Affiliation(s)
- Wenqiang Zhou
- School of Physics, Zhejiang University, Hangzhou 310027, China
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
| | - Jiannan Hua
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
| | - Naitian Liu
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
| | - Jing Ding
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
| | - Hanxiao Xiang
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
| | - Wei Zhu
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
| | - Shuigang Xu
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou 310024, Zhejiang Province, China
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4
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Yao H, Zheng P, Zhang S, Hu C, Fang X, Zhang L, Ling D, Chen H, Ou X. Twist piezoelectricity: giant electromechanical coupling in magic-angle twisted bilayer LiNbO 3. Nat Commun 2024; 15:5002. [PMID: 38866740 PMCID: PMC11169249 DOI: 10.1038/s41467-024-49321-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Accepted: 06/03/2024] [Indexed: 06/14/2024] Open
Abstract
Twisted a pair of stacked two-dimensional materials exhibit many exotic electronic and photonic properties, leading to the emergence of flat-band superconductivity, moiré engineering and topological polaritons. These remarkable discoveries make twistronics the focus point of tremendous interest, but mostly limited to the concept of electrons, phonons or photons. Here, we present twist piezoelectricity as a fascinating paradigm to modulate polarization and electromechanical coupling by twisting precisely the stacked lithium niobate slabs due to the interlayer coupling effect. Particularly, the inversed and twisted bilayer lithium niobate is constructed to overcome the intrinsic mutual limitation of single crystals and giant effective electromechanical coupling coefficientk t 2 is unveiled at magic angle of 11 1 ∘ , reaching 85.5%. Theoretical analysis based on mutual energy integrals shows well agreements with numerical and experimental results. Our work opens new venues to flexibly control multi-physics with magic angle, stimulating progress in wideband acoustic-electric, and acoustic-optic components, which has great potential in wireless communication, timing, sensing, and hybrid integrated photonics.
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Affiliation(s)
- Hulin Yao
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China
- The Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China
| | - Pengcheng Zheng
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China
- The Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China
| | - Shibin Zhang
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China.
| | - Chuanjie Hu
- Department of Physics & Department of Microelectronics and Integrated Circuit, Xiamen University, 422 Siming South Road, Xiamen, 361005, China
| | - Xiaoli Fang
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China
- The Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China
| | - Liping Zhang
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China
| | - Dan Ling
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China
- The Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China
| | - Huanyang Chen
- Department of Physics & Department of Microelectronics and Integrated Circuit, Xiamen University, 422 Siming South Road, Xiamen, 361005, China.
- Department of Physics, Xiamen University Malaysia, Sepang, Malaysia.
| | - Xin Ou
- State Key Laboratory of Materials for Integrated Circuits, Chinese Academy of Sciences, 865 Changning Road, Shanghai, 200050, China.
- The Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China.
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5
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Lu H, Chen BB, Wu HQ, Sun K, Meng ZY. Thermodynamic Response and Neutral Excitations in Integer and Fractional Quantum Anomalous Hall States Emerging from Correlated Flat Bands. PHYSICAL REVIEW LETTERS 2024; 132:236502. [PMID: 38905653 DOI: 10.1103/physrevlett.132.236502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 04/26/2024] [Accepted: 05/14/2024] [Indexed: 06/23/2024]
Abstract
Integer and fractional Chern insulators have been extensively explored in correlated flat band models. Recently, the prediction and experimental observation of fractional quantum anomalous Hall (FQAH) states with spontaneous time-reversal symmetry breaking have garnered attention. While the thermodynamics of integer quantum anomalous Hall (IQAH) states have been systematically studied, our theoretical knowledge on thermodynamic properties of FQAH states has been severely limited. Here, we delve into the general thermodynamic response and collective excitations of both IQAH and FQAH states within the paradigmatic flat Chern-band model with remote band considered. Our key findings include (i) in both ν=1 IQAH and ν=1/3 FQAH states, even without spin fluctuations, the charge-neutral collective excitations would lower the onset temperature of these topological states, to a value significantly smaller than the charge gap, due to band mixing and multiparticle scattering; (ii) by employing large-scale thermodynamic simulations in FQAH states in the presence of strong interband mixing between C=±1 bands, we find that the lowest collective excitations manifest as the zero-momentum excitons in the IQAH state, whereas in the FQAH state, they take the form of magnetorotons with finite momentum; (iii) the unique charge oscillations in FQAH states are exhibited with distinct experimental signatures, which we propose to detect in future experiments.
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6
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Zeng Y, Guerci D, Crépel V, Millis AJ, Cano J. Sublattice Structure and Topology in Spontaneously Crystallized Electronic States. PHYSICAL REVIEW LETTERS 2024; 132:236601. [PMID: 38905641 DOI: 10.1103/physrevlett.132.236601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 05/13/2024] [Accepted: 05/16/2024] [Indexed: 06/23/2024]
Abstract
The prediction and realization of the quantum anomalous Hall effect are often intimately connected to honeycomb lattices in which the sublattice degree of freedom plays a central role in the nontrivial topology. Two-dimensional Wigner crystals, on the other hand, form triangular lattices without sublattice degrees of freedom, resulting in a topologically trivial state. Here, we discuss the possibility of spontaneously formed honeycomb-lattice crystals that exhibit the quantum anomalous Hall effect. Starting from a single-band system with nontrivial quantum geometry, we derive the mean-field energy functional of a class of crystal states and express it as a model of sublattice pseudospins in momentum space. We find that nontrivial quantum geometry leads to extra terms in the pseudospin model that break an effective "time-reversal symmetry" and favor a topologically nontrivial pseudospin texture. When the effects of these extra terms dominate over the ferromagnetic exchange coupling between pseudospins, the anomalous Hall crystal state becomes energetically favorable over the trivial Wigner crystal state.
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7
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Yuan Y, Liu L, Zhu J, Dong J, Chu Y, Wu F, Du L, Watanabe K, Taniguchi T, Shi D, Zhang G, Yang W. Interplay of Landau Quantization and Interminivalley Scatterings in a Weakly Coupled Moiré Superlattice. NANO LETTERS 2024; 24:6722-6729. [PMID: 38717299 PMCID: PMC11157648 DOI: 10.1021/acs.nanolett.4c01411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2024] [Revised: 05/02/2024] [Accepted: 05/02/2024] [Indexed: 06/06/2024]
Abstract
Double-layer quantum systems are promising platforms for realizing novel quantum phases. Here, we report a study of quantum oscillations (QOs) in a weakly coupled double-layer system composed of a large-angle twisted-double-bilayer graphene (TDBG). We quantify the interlayer coupling strength by measuring the interlayer capacitance from the QOs pattern at low temperatures, revealing electron-hole asymmetry. At high temperatures when SdHOs are thermally smeared, we observe resistance peaks when Landau levels (LLs) from two moiré minivalleys are aligned, regardless of carrier density; eventually, it results in a 2-fold increase of oscillating frequency in D, serving as compelling evidence of the magneto-intersub-band oscillations (MISOs) in double-layer systems. The temperature dependence of MISOs suggests that electron-electron interactions play a crucial role and the scattering times obtained from MISO thermal damping are correlated with the interlayer coupling strength. Our study reveals intriguing interplays among Landau quantization, moiré band structure, and scatterings.
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Affiliation(s)
- Yalong Yuan
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Le Liu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Jundong Zhu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Jingwei Dong
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Yanbang Chu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Fanfan Wu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Luojun Du
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Kenji Watanabe
- Research
Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research
Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Dongxia Shi
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
- Songshan
Lake Materials Laboratory, Dongguan 523808, People’s
Republic of China
| | - Guangyu Zhang
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
- Songshan
Lake Materials Laboratory, Dongguan 523808, People’s
Republic of China
| | - Wei Yang
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
- Songshan
Lake Materials Laboratory, Dongguan 523808, People’s
Republic of China
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8
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Zhou HT, Li CY, Zhu JH, Hu C, Wang YF, Wang YS, Qiu CW. Dynamic Acoustic Beamshaping with Coupling-Immune Moiré Metasurfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2313004. [PMID: 38382460 DOI: 10.1002/adma.202313004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 01/28/2024] [Indexed: 02/23/2024]
Abstract
Moiré effects arising from mutually twisted metasurfaces have showcased remarkable wave manipulation capabilities, unveiling tantalizing emerging phenomena such as acoustic moiré flat bands and topological phase transitions. However, the pursuit of strong near-field coupling in layers has necessitated acoustic moiré metasurfaces to be tightly stacked at narrow distances in the subwavelength range. Here, moiré effects beyond near-field interlayer coupling in acoustics are reported and the concept of coupling-immune moiré metasurfaces is proposed. Remote acoustic moiré effects decoupled from the interlayer distance are theoretically, numerically, and experimentally demonstrated. Tunable out-of-plane acoustic beam scanning is successfully achieved by dynamically controlling twist angles. The engineered coupling-immune properties are further extended to multilayered acoustic moiré metasurfaces and manipulation of acoustic vortices. Good robustness against external disturbances is also observed for the fabricated coupling-immune acoustic moiré metasurfaces. The presented work unlocks the potential of twisted moiré devices for out-of-plane acoustic beam shaping, enabling practical applications in remote dynamic detection, and multiplexed underwater acoustic communication.
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Affiliation(s)
- Hong-Tao Zhou
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117583
| | - Chen-Yang Li
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
| | - Jia-Hui Zhu
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
| | - Chuanjie Hu
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117583
- Institute of Electromagnetics and Acoustics, School of Electronic Science and Engineering, Xiamen University, Xiamen, 361005, China
| | - Yan-Feng Wang
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
| | - Yue-Sheng Wang
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, 300350, China
- Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing, 100044, China
| | - Cheng-Wei Qiu
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117583
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9
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Almoalem A, Feldman I, Mangel I, Shlafman M, Yaish YE, Fischer MH, Moshe M, Ruhman J, Kanigel A. The observation of π-shifts in the Little-Parks effect in 4Hb-TaS 2. Nat Commun 2024; 15:4623. [PMID: 38816364 PMCID: PMC11139670 DOI: 10.1038/s41467-024-48260-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Accepted: 04/23/2024] [Indexed: 06/01/2024] Open
Abstract
Finding evidence of non-trivial pairing states is one of the greatest experimental challenges in the field of unconventional superconductivity. Such evidence requires phase-sensitive probes susceptible to the internal structure of the order parameter. We report the measurement of the Little-Parks effect in the unconventional superconductor candidate 4Hb-TaS2. In half of our rings, which are fabricated from single-crystals, we find a π-shift in the transition-temperature oscillations. According to theory, such a π-shift is only possible if the order parameter is non-s-wave. In the absence of crystallographic defects, the shift provides evidence of a multi-component order parameter. Thus, this observation increases the likelihood of the two-component order parameter scenario in 4Hb-TaS2. Furthermore, we show that Tc is enhanced as a function of the out-of-plane field when a constant in-plane field is applied, which we explain using a two-component order-parameter.
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Affiliation(s)
- Avior Almoalem
- Physics Department, Technion-Israel Institute of Technology, Haifa, 32000, Israel
| | - Irena Feldman
- Physics Department, Technion-Israel Institute of Technology, Haifa, 32000, Israel
| | - Ilay Mangel
- Physics Department, Technion-Israel Institute of Technology, Haifa, 32000, Israel
| | - Michael Shlafman
- Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering, Technion, Haifa, 32000, Israel
| | - Yuval E Yaish
- Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering, Technion, Haifa, 32000, Israel
| | - Mark H Fischer
- Department of Physics, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Michael Moshe
- Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel
| | - Jonathan Ruhman
- Department of Physics, Bar-Ilan University, 52900, Ramat Gan, Israel
| | - Amit Kanigel
- Physics Department, Technion-Israel Institute of Technology, Haifa, 32000, Israel.
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10
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Han X, Liu Q, Wang Y, Niu R, Qu Z, Wang Z, Li Z, Han C, Watanabe K, Taniguchi T, Song Z, Liu J, Mao J, Han Z, Chittari BL, Jung J, Gan Z, Lu J. Engineering the Band Topology in a Rhombohedral Trilayer Graphene Moiré Superlattice. NANO LETTERS 2024; 24:6286-6295. [PMID: 38747346 DOI: 10.1021/acs.nanolett.4c00948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2024]
Abstract
Moiré superlattices have become a fertile playground for topological Chern insulators, where the displacement field can tune the quantum geometry and Chern number of the topological band. However, in experiments, displacement field engineering of spontaneous symmetry-breaking Chern bands has not been demonstrated. Here in a rhombohedral trilayer graphene moiré superlattice, we use a thermodynamic probe and transport measurement to monitor the Chern number evolution as a function of the displacement field. At a quarter filling of the moiré band, a novel Chern number of three is unveiled to compete with the well-established number of two upon turning on the electric field and survives when the displacement field is sufficiently strong. The transition can be reconciled by a nematic instability on the Fermi surface due to the pseudomagnetic vector field potentials associated with moiré strain patterns. Our work opens more opportunities to active control of Chern numbers in van der Waals moiré systems.
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Affiliation(s)
- Xiangyan Han
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Qianling Liu
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Yijie Wang
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Ruirui Niu
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Zhuangzhuang Qu
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Zhiyu Wang
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Zhuoxian Li
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Chunrui Han
- Institute of Microelectronics, Chinese Academy of Sciences, Beijing, 100029, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Zhida Song
- International Center for Quantum Materials, Peking University, Beijing 100871, China
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 200031, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 200031, China
| | - Jinhai Mao
- School of Physical Sciences and CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zheng Han
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Optoelectronics, Shanxi University, Taiyuan 030006, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
| | - Bheema Lingam Chittari
- Department of Physical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, West Bengal, India
| | - Jeil Jung
- Department of Physics, University of Seoul, Seoul 02504, Korea
- Department of Smart Cities, University of Seoul, Seoul 02504, Korea
| | - Zizhao Gan
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
| | - Jianming Lu
- State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
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11
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Zhang XW, Wang C, Liu X, Fan Y, Cao T, Xiao D. Polarization-driven band topology evolution in twisted MoTe 2 and WSe 2. Nat Commun 2024; 15:4223. [PMID: 38762554 PMCID: PMC11102499 DOI: 10.1038/s41467-024-48511-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 05/02/2024] [Indexed: 05/20/2024] Open
Abstract
Motivated by recent experimental observations of opposite Chern numbers in R-type twisted MoTe2 and WSe2 homobilayers, we perform large-scale density-functional-theory calculations with machine learning force fields to investigate moiré band topology across a range of twist angles in both materials. We find that the Chern numbers of the moiré frontier bands change sign as a function of twist angle, and this change is driven by the competition between moiré ferroelectricity and piezoelectricity. Our large-scale calculations, enabled by machine learning methods, reveal crucial insights into interactions across different scales in twisted bilayer systems. The interplay between atomic-level relaxation effects and moiré-scale electrostatic potential variation opens new avenues for the design of intertwined topological and correlated states, including the possibility of mimicking higher Landau level physics in the absence of magnetic field.
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Affiliation(s)
- Xiao-Wei Zhang
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
| | - Chong Wang
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
| | - Xiaoyu Liu
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
| | - Yueyao Fan
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA
| | - Ting Cao
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA.
| | - Di Xiao
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA.
- Department of Physics, University of Washington, Seattle, WA, 98195, USA.
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12
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Xiong R, Brantly SL, Su K, Nie JH, Zhang Z, Banerjee R, Ruddick H, Watanabe K, Taniguchi T, Tongay SA, Xu C, Jin C. Tunable exciton valley-pseudospin orders in moiré superlattices. Nat Commun 2024; 15:4254. [PMID: 38762501 PMCID: PMC11102517 DOI: 10.1038/s41467-024-48725-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Accepted: 05/13/2024] [Indexed: 05/20/2024] Open
Abstract
Excitons in two-dimensional (2D) semiconductors have offered an attractive platform for optoelectronic and valleytronic devices. Further realizations of correlated phases of excitons promise device concepts not possible in the single particle picture. Here we report tunable exciton "spin" orders in WSe2/WS2 moiré superlattices. We find evidence of an in-plane (xy) order of exciton "spin"-here, valley pseudospin-around exciton filling vex = 1, which strongly suppresses the out-of-plane "spin" polarization. Upon increasing vex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic (FM-z) spin order that spontaneously enhances the "spin" polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose-Hubbard model and is distinct from the fermion case. Our study paves the way for engineering exotic phases of matter from correlated spinor bosons, opening the door to a host of unconventional quantum devices.
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Affiliation(s)
- Richen Xiong
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Samuel L Brantly
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Kaixiang Su
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Jacob H Nie
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Zihan Zhang
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Rounak Banerjee
- School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, AZ, USA
| | - Hayley Ruddick
- School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, AZ, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Seth Ariel Tongay
- School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, AZ, USA
| | - Cenke Xu
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Chenhao Jin
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA, USA.
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13
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Ip CIJ, Gao Q, Nguyen KD, Yan C, Yan G, Hoenig E, Marchese TS, Zhang M, Lee W, Rokni H, Meng YS, Liu C, Yang S. Preservation of Topological Surface States in Millimeter-Scale Transferred Membranes. NANO LETTERS 2024. [PMID: 38758657 DOI: 10.1021/acs.nanolett.4c00008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2024]
Abstract
Ultrathin topological insulator membranes are building blocks of exotic quantum matter. However, traditional epitaxy of these materials does not facilitate stacking in arbitrary orders, while mechanical exfoliation from bulk crystals is also challenging due to the non-negligible interlayer coupling therein. Here we liberate millimeter-scale films of the topological insulator Bi2Se3, grown by molecular beam epitaxy, down to 3 quintuple layers. We characterize the preservation of the topological surface states and quantum well states in transferred Bi2Se3 films using angle-resolved photoemission spectroscopy. Leveraging the photon-energy-dependent surface sensitivity, the photoemission spectra taken with 6 and 21.2 eV photons reveal a transfer-induced migration of the topological surface states from the top to the inner layers. By establishing clear electronic structures of the transferred films and unveiling the wave function relocation of the topological surface states, our work lays the physics foundation crucial for the future fabrication of artificially stacked topological materials with single-layer precision.
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Affiliation(s)
- Chi Ian Jess Ip
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Qiang Gao
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Khanh Duy Nguyen
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Chenhui Yan
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Gangbin Yan
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Eli Hoenig
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Thomas S Marchese
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Minghao Zhang
- Department of NanoEngineering, University of California San Diego, La Jolla, California 92093, United States
| | - Woojoo Lee
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Hossein Rokni
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Ying Shirley Meng
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
- Department of NanoEngineering, University of California San Diego, La Jolla, California 92093, United States
| | - Chong Liu
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
| | - Shuolong Yang
- Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States
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14
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Zhang H, Li Q, Park Y, Jia Y, Chen W, Li J, Liu Q, Bao C, Leconte N, Zhou S, Wang Y, Watanabe K, Taniguchi T, Avila J, Dudin P, Yu P, Weng H, Duan W, Wu Q, Jung J, Zhou S. Observation of dichotomic field-tunable electronic structure in twisted monolayer-bilayer graphene. Nat Commun 2024; 15:3737. [PMID: 38702313 PMCID: PMC11068895 DOI: 10.1038/s41467-024-48166-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 04/22/2024] [Indexed: 05/06/2024] Open
Abstract
Twisted bilayer graphene (tBLG) provides a fascinating platform for engineering flat bands and inducing correlated phenomena. By designing the stacking architecture of graphene layers, twisted multilayer graphene can exhibit different symmetries with rich tunability. For example, in twisted monolayer-bilayer graphene (tMBG) which breaks the C2z symmetry, transport measurements reveal an asymmetric phase diagram under an out-of-plane electric field, exhibiting correlated insulating state and ferromagnetic state respectively when reversing the field direction. Revealing how the electronic structure evolves with electric field is critical for providing a better understanding of such asymmetric field-tunable properties. Here we report the experimental observation of field-tunable dichotomic electronic structure of tMBG by nanospot angle-resolved photoemission spectroscopy (NanoARPES) with operando gating. Interestingly, selective enhancement of the relative spectral weight contributions from monolayer and bilayer graphene is observed when switching the polarity of the bias voltage. Combining experimental results with theoretical calculations, the origin of such field-tunable electronic structure, resembling either tBLG or twisted double-bilayer graphene (tDBG), is attributed to the selectively enhanced contribution from different stacking graphene layers with a strong electron-hole asymmetry. Our work provides electronic structure insights for understanding the rich field-tunable physics of tMBG.
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Affiliation(s)
- Hongyun Zhang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Qian Li
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Youngju Park
- Department of Physics, University of Seoul, Seoul, 02504, Korea
| | - Yujin Jia
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, PR China
- University of Chinese Academy of Sciences, Beijing, 100049, PR China
| | - Wanying Chen
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Jiaheng Li
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, PR China
- University of Chinese Academy of Sciences, Beijing, 100049, PR China
| | - Qinxin Liu
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Changhua Bao
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Nicolas Leconte
- Department of Physics, University of Seoul, Seoul, 02504, Korea
| | - Shaohua Zhou
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Yuan Wang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Jose Avila
- Synchrotron SOLEIL, L'Orme des Merisiers, Departamentale 128, 91190, Saint-Aubin, France
| | - Pavel Dudin
- Synchrotron SOLEIL, L'Orme des Merisiers, Departamentale 128, 91190, Saint-Aubin, France
| | - Pu Yu
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
- Frontier Science Center for Quantum Information, Beijing, 100084, PR China
| | - Hongming Weng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, PR China
- University of Chinese Academy of Sciences, Beijing, 100049, PR China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, PR China
| | - Wenhui Duan
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China
- Frontier Science Center for Quantum Information, Beijing, 100084, PR China
- Institute for Advanced Study, Tsinghua University, Beijing, 100084, PR China
| | - Quansheng Wu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, PR China
- University of Chinese Academy of Sciences, Beijing, 100049, PR China
| | - Jeil Jung
- Department of Physics, University of Seoul, Seoul, 02504, Korea
- Department of Smart Cities, University of Seoul, Seoul, 02504, Korea
| | - Shuyun Zhou
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, PR China.
- Frontier Science Center for Quantum Information, Beijing, 100084, PR China.
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15
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Yao YT, Xu SY, Chang TR. Atomic scale quantum anomalous hall effect in monolayer graphene/MnBi 2Te 4 heterostructure. MATERIALS HORIZONS 2024. [PMID: 38691397 DOI: 10.1039/d4mh00165f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2024]
Abstract
The two-dimensional quantum anomalous Hall (QAH) effect is direct evidence of non-trivial Berry curvature topology in condensed matter physics. Searching for QAH in 2D materials, particularly with simplified fabrication methods, poses a significant challenge in future applications. Despite numerous theoretical works proposed for the QAH effect with C = 2 in graphene, neglecting magnetism sources such as proper substrate effects lacks experimental evidence. In this work, we propose the QAH effect in graphene/MnBi2Te4 (MBT) heterostructure based on density-functional theory (DFT) calculations. The monolayer MBT introduces spin-orbital coupling, Zeeman exchange field, and Kekulé distortion as a substrate effect into graphene, resulting in QAH with C = 1 in the heterostructure. Our effective Hamiltonian further presents a rich phase diagram that has not been studied previously. Our work provides a new and practical way to explore the QAH effect in monolayer graphene and the magnetic topological phases by the flexibility of MBT family materials.
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Affiliation(s)
- Yueh-Ting Yao
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
| | - Su-Yang Xu
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
| | - Tay-Rong Chang
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
- Center for Quantum Frontiers of Research and Technology (QFort), Tainan 701, Taiwan
- Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
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16
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Dong W, Dai Z, Liu L, Zhang Z. Toward Clean 2D Materials and Devices: Recent Progress in Transfer and Cleaning Methods. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024; 36:e2303014. [PMID: 38049925 DOI: 10.1002/adma.202303014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Revised: 08/30/2023] [Indexed: 12/06/2023]
Abstract
Two-dimensional (2D) materials have tremendous potential to revolutionize the field of electronics and photonics. Unlocking such potential, however, is hampered by the presence of contaminants that usually impede the performance of 2D materials in devices. This perspective provides an overview of recent efforts to develop clean 2D materials and devices. It begins by discussing conventional and recently developed wet and dry transfer techniques and their effectiveness in maintaining material "cleanliness". Multi-scale methodologies for assessing the cleanliness of 2D material surfaces and interfaces are then reviewed. Finally, recent advances in passive and active cleaning strategies are presented, including the unique self-cleaning mechanism, thermal annealing, and mechanical treatment that rely on self-cleaning in essence. The crucial role of interface wetting in these methods is emphasized, and it is hoped that this understanding can inspire further extension and innovation of efficient transfer and cleaning of 2D materials for practical applications.
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Affiliation(s)
- Wenlong Dong
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication and CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Zhaohe Dai
- Department of Mechanics and Engineering Science, State Key Laboratory for Turbulence and Complex Systems, College of Engineering, Peking University, Beijing, 100871, China
| | - Luqi Liu
- CAS Key Laboratory of Nanosystem and Hierarchical Fabrication and CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Zhong Zhang
- CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, 230027, China
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17
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Foutty BA, Kometter CR, Devakul T, Reddy AP, Watanabe K, Taniguchi T, Fu L, Feldman BE. Mapping twist-tuned multiband topology in bilayer WSe 2. Science 2024; 384:343-347. [PMID: 38669569 DOI: 10.1126/science.adi4728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Accepted: 03/19/2024] [Indexed: 04/28/2024]
Abstract
Semiconductor moiré superlattices have been shown to host a wide array of interaction-driven ground states. However, twisted homobilayers have been difficult to study in the limit of large moiré wavelengths, where interactions are most dominant. In this study, we conducted local electronic compressibility measurements of twisted bilayer WSe2 (tWSe2) at small twist angles. We demonstrated multiple topological bands that host a series of Chern insulators at zero magnetic field near a "magic angle" around 1.23°. Using a locally applied electric field, we induced a topological quantum-phase transition at one hole per moiré unit cell. Our work establishes the topological phase diagram of a generalized Kane-Mele-Hubbard model in tWSe2, demonstrating a tunable platform for strongly correlated topological phases.
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Affiliation(s)
- Benjamin A Foutty
- Geballe Laboratory for Advanced Materials, Stanford, CA 94305, USA
- Department of Physics, Stanford University, Stanford, CA 94305, USA
| | - Carlos R Kometter
- Geballe Laboratory for Advanced Materials, Stanford, CA 94305, USA
- Department of Physics, Stanford University, Stanford, CA 94305, USA
| | - Trithep Devakul
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Aidan P Reddy
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Benjamin E Feldman
- Geballe Laboratory for Advanced Materials, Stanford, CA 94305, USA
- Department of Physics, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
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18
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Matsuoka H, Kajihara S, Nomoto T, Wang Y, Hirayama M, Arita R, Iwasa Y, Nakano M. Band-driven switching of magnetism in a van der Waals magnetic semimetal. SCIENCE ADVANCES 2024; 10:eadk1415. [PMID: 38608018 PMCID: PMC11014443 DOI: 10.1126/sciadv.adk1415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 03/13/2024] [Indexed: 04/14/2024]
Abstract
Magnetic semimetals form an attractive class of materials because of the nontrivial contributions of itinerant electrons to magnetism. Because of their relatively low-carrier-density nature, a doping level of those materials could be largely tuned by a gating technique. Here, we demonstrate gate-tunable ferromagnetism in an emergent van der Waals magnetic semimetal Cr3Te4 based on an ion-gating technique. Upon doping electrons into the system, the Curie temperature (TC) sharply increases, approaching near to room temperature, and then decreases to some extent. This non-monotonous variation of TC accompanies the switching of the magnetic anisotropy, synchronously followed by the sign changes of the ordinary and anomalous Hall effects. Those results clearly elucidate that the magnetism in Cr3Te4 should be governed by its semimetallic band nature.
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Affiliation(s)
- Hideki Matsuoka
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - Shun Kajihara
- Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Takuya Nomoto
- Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo 153-8904, Japan
| | - Yue Wang
- Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Motoaki Hirayama
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Ryotaro Arita
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo 153-8904, Japan
| | - Yoshihiro Iwasa
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
| | - Masaki Nakano
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
- Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
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19
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Fumega AO, Lado JL. Nature of the Unconventional Heavy-Fermion Kondo State in Monolayer CeSiI. NANO LETTERS 2024; 24:4272-4278. [PMID: 38394370 PMCID: PMC11010227 DOI: 10.1021/acs.nanolett.4c00619] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Revised: 02/14/2024] [Accepted: 02/15/2024] [Indexed: 02/25/2024]
Abstract
CeSiI has been recently isolated in the ultrathin limit, establishing CeSiI as the first intrinsic two-dimensional van der Waals heavy-fermion material up to 85 K. We show that, due to the strong spin-orbit coupling, the local moments develop a multipolar real-space magnetic texture, leading to local pseudospins with a nearly vanishing net moment. To elucidate its Kondo-screened regime, we extract from first-principles the parameters of the Kondo lattice model describing this material. We develop a pseudofermion methodology in combination with ab initio calculations to reveal the nature of the heavy-fermion state in CeSiI. We analyze the competing magnetic interactions leading to an unconventional heavy-fermion order as a function of the magnetic exchange between the localized f-electrons and the strength of the Kondo coupling. Our results show that the magnetic exchange interactions promote an unconventional momentum-dependent Kondo-screened phase, establishing the nature of the heavy-fermion state observed in CeSiI.
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Affiliation(s)
- Adolfo O. Fumega
- Department of Applied
Physics, Aalto University, 02150 Espoo, Finland
| | - Jose L. Lado
- Department of Applied
Physics, Aalto University, 02150 Espoo, Finland
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20
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Mitra S, Jiménez-Galán Á, Aulich M, Neuhaus M, Silva REF, Pervak V, Kling MF, Biswas S. Light-wave-controlled Haldane model in monolayer hexagonal boron nitride. Nature 2024; 628:752-757. [PMID: 38622268 PMCID: PMC11041748 DOI: 10.1038/s41586-024-07244-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 02/27/2024] [Indexed: 04/17/2024]
Abstract
In recent years, the stacking and twisting of atom-thin structures with matching crystal symmetry has provided a unique way to create new superlattice structures in which new properties emerge1,2. In parallel, control over the temporal characteristics of strong light fields has allowed researchers to manipulate coherent electron transport in such atom-thin structures on sublaser-cycle timescales3,4. Here we demonstrate a tailored light-wave-driven analogue to twisted layer stacking. Tailoring the spatial symmetry of the light waveform to that of the lattice of a hexagonal boron nitride monolayer and then twisting this waveform result in optical control of time-reversal symmetry breaking5 and the realization of the topological Haldane model6 in a laser-dressed two-dimensional insulating crystal. Further, the parameters of the effective Haldane-type Hamiltonian can be controlled by rotating the light waveform, thus enabling ultrafast switching between band structure configurations and allowing unprecedented control over the magnitude, location and curvature of the bandgap. This results in an asymmetric population between complementary quantum valleys that leads to a measurable valley Hall current7, which can be detected by optical harmonic polarimetry. The universality and robustness of our scheme paves the way to valley-selective bandgap engineering on the fly and unlocks the possibility of creating few-femtosecond switches with quantum degrees of freedom.
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Affiliation(s)
- Sambit Mitra
- Max Planck Institute of Quantum Optics, Garching, Germany
- Physics Department, Ludwig-Maximilian University of Munich, Garching, Germany
| | - Álvaro Jiménez-Galán
- Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain.
- Max Born Institute, Berlin, Germany.
| | - Mario Aulich
- Physics Department, Ludwig-Maximilian University of Munich, Garching, Germany
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Marcel Neuhaus
- Max Planck Institute of Quantum Optics, Garching, Germany
- Physics Department, Ludwig-Maximilian University of Munich, Garching, Germany
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Rui E F Silva
- Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
| | - Volodymyr Pervak
- Max Planck Institute of Quantum Optics, Garching, Germany
- Physics Department, Ludwig-Maximilian University of Munich, Garching, Germany
| | - Matthias F Kling
- Max Planck Institute of Quantum Optics, Garching, Germany
- Physics Department, Ludwig-Maximilian University of Munich, Garching, Germany
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA
- Department of Applied Physics, Stanford University, Stanford, CA, USA
| | - Shubhadeep Biswas
- Max Planck Institute of Quantum Optics, Garching, Germany.
- Physics Department, Ludwig-Maximilian University of Munich, Garching, Germany.
- SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
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21
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Yang K, Xu Z, Feng Y, Schindler F, Xu Y, Bi Z, Bernevig BA, Tang P, Liu CX. Topological minibands and interaction driven quantum anomalous Hall state in topological insulator based moiré heterostructures. Nat Commun 2024; 15:2670. [PMID: 38531879 DOI: 10.1038/s41467-024-46717-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 02/29/2024] [Indexed: 03/28/2024] Open
Abstract
The presence of topological flat minibands in moiré materials provides an opportunity to explore the interplay between topology and correlation. In this work, we study moiré minibands in topological insulator films with two hybridized surface states under a moiré superlattice potential created by two-dimensional insulating materials. We show the lowest conduction (highest valence) Kramers' pair of minibands can beZ 2 non-trivial when the minima (maxima) of moiré potential approximately form a hexagonal lattice with six-fold rotation symmetry. Coulomb interaction can drive the non-trivial Kramers' minibands into the quantum anomalous Hall state when they are half-filled, which is further stabilized by applying external gate voltages to break inversion. We propose the monolayer Sb2 on top of Sb2Te3 films as a candidate based on first principles calculations. Our work demonstrates the topological insulator based moiré heterostructure as a potential platform for studying interacting topological phases.
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Affiliation(s)
- Kaijie Yang
- Department of Physics, the Pennsylvania State University, University Park, PA, 16802, USA
| | - Zian Xu
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
| | - Yanjie Feng
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
| | - Frank Schindler
- Blackett Laboratory, Imperial College London, London, SW7 2AZ, United Kingdom
| | - Yuanfeng Xu
- Center for Correlated Matter and School of Physics, Zhejiang University, Hangzhou, 310058, China
- Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - Zhen Bi
- Department of Physics, the Pennsylvania State University, University Park, PA, 16802, USA
| | - B Andrei Bernevig
- Department of Physics, Princeton University, Princeton, NJ, 08544, USA
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018, Donostia-San Sebastian, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - Peizhe Tang
- School of Materials Science and Engineering, Beihang University, Beijing, 100191, China
- Max Planck Institute for the Structure and Dynamics of Matter and Center for Free Electron Laser Science, Hamburg, 22761, Germany
| | - Chao-Xing Liu
- Department of Physics, the Pennsylvania State University, University Park, PA, 16802, USA.
- Department of Physics, Princeton University, Princeton, NJ, 08544, USA.
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22
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Zhou W, Ding J, Hua J, Zhang L, Watanabe K, Taniguchi T, Zhu W, Xu S. Layer-polarized ferromagnetism in rhombohedral multilayer graphene. Nat Commun 2024; 15:2597. [PMID: 38519502 PMCID: PMC10960043 DOI: 10.1038/s41467-024-46913-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 03/14/2024] [Indexed: 03/25/2024] Open
Abstract
Flat-band systems with strongly correlated electrons can exhibit a variety of phenomena, such as correlated insulating and topological states, unconventional superconductivity, and ferromagnetism. Rhombohedral multilayer graphene has recently emerged as a promising platform for investigating exotic quantum states due to its hosting of topologically protected surface flat bands at low energy, which have a layer-dependent energy dispersion. However, the complex relationship between the surface flat bands and the highly dispersive high-energy bands makes it difficult to study correlated surface states. In this study, we introduce moiré superlattices as a method to isolate the surface flat bands of rhombohedral multilayer graphene. The observed pronounced screening effects in the moiré potential-modulated rhombohedral multilayer graphene indicate that the two surface states are electronically decoupled. The flat bands that are isolated promote correlated surface states in areas that are distant from the charge neutrality points. Notably, we observe tunable layer-polarized ferromagnetism, which is evidenced by a hysteretic anomalous Hall effect. This is achieved by polarizing the surface states with finite displacement fields.
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Affiliation(s)
- Wenqiang Zhou
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
| | - Jing Ding
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
| | - Jiannan Hua
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
| | - Le Zhang
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Wei Zhu
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China.
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China.
| | - Shuigang Xu
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China.
- Institute of Natural Sciences, Westlake Institute for Advanced Study, 18 Shilongshan Road, Hangzhou, 310024, Zhejiang Province, China.
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23
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Fan G, Wu Y, Tong J, Deng L, Yin X, Tian F, Zhang X. Influence of electronic correlation on the valley and topological properties of VSiGeP 4 monolayer. Phys Chem Chem Phys 2024; 26:9628-9635. [PMID: 38466239 DOI: 10.1039/d3cp04739c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
Valley is used as a new degree of freedom for information encoding and storage. In this work, the valley and topological properties of the VSiGeP4 monolayer were studied by adjusting the U value based on first-principles calculations. The VSiGeP4 monolayer remains in a ferromagnetic ground state regardless of the change in the U value. The magnetic anisotropy of the VSiGeP4 monolayer is initially in-plane, and then turns out-of-plane with the increase in the U value. Moreover, a topological phase transition is observed in the present VSiGeP4 monolayer with the increase in U value from 0 to 3 eV, i.e., the VSiGeP4 monolayer behaves as a bipolar magnetic semiconductor, a ferrovalley semiconductor, a half-valley metal characteristic, and a quantum anomalous Hall state. The mechanism of the topological phase transition behavior of the VSiGeP4 monolayer was analyzed. It was found that the variation in U values would change the strength of the electronic correlation effect, resulting in the valley and topological properties. In addition, carrier doping was studied to design a valleytronic device using this VSiGeP4 monolayer. By doping 0.05 electrons per f.u., the VSiGeP4 monolayer with a U value of 3 eV exhibits 100% spin polarization. This study indicates that the VSiGeP4 monolayer has potential applications in spintronic, valleytronic, and topological electronic nanodevices.
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Affiliation(s)
- Guangxin Fan
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Yanzhao Wu
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Junwei Tong
- Department of Physics, Freie Universität Berlin, Berlin 14195, Germany
| | - Li Deng
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Xiang Yin
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
| | - Fubo Tian
- State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
| | - Xianmin Zhang
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
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24
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Liu Y, Feng Y, Dai Y, Huang B, Ma Y. Engineering Layertronics in Two-Dimensional Ferromagnetic Multiferroic Lattice. NANO LETTERS 2024; 24:3507-3514. [PMID: 38445582 DOI: 10.1021/acs.nanolett.4c00436] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
Layertronics, rooted in the layer Hall effect (LHE), is an emerging fundamental phenomenon in condensed matter physics and spintronics. So far, several theoretical and experimental proposals have been made to realize LHE, but all are based on antiferromagnetic systems. Here, using symmetry and tight-binding model analysis, we propose a general mechanism for engineering layertronics in a two-dimensional ferromagnetic multiferroic lattice. The physics is related to the band geometric properties and multiferroicity, which results in the coupling between Berry curvature and layer degree of freedom, thereby generating the LHE. Using first-principles calculations, we further demonstrate this mechanism in bilayer (BL) TcIrGe2S6. Due to the intrinsic inversion and time-reversal symmetry breakings, BL TcIrGe2S6 exhibits multiferroicity with large Berry curvatures at both the center and corners of the Brillouin zone. These Berry curvatures couple with the layer physics, forming the LHE in BL TcIrGe2S6. Our work opens a new direction for research on layertronics.
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Affiliation(s)
- Yibo Liu
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China
| | - Yangyang Feng
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China
| | - Ying Dai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China
| | - Baibiao Huang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China
| | - Yandong Ma
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Shandanan Str. 27, Jinan 250100, People's Republic of China
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25
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Li K, Yin LJ, Che C, Zhang S, Liu X, Xiao Y, Liu S, Tong Q, Li SY, Pan A. Correlation-Induced Symmetry-Broken States in Large-Angle Twisted Bilayer Graphene on MoS 2. ACS NANO 2024; 18:7937-7944. [PMID: 38441035 DOI: 10.1021/acsnano.3c09993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/06/2024]
Abstract
Strongly correlated states commonly emerge in twisted bilayer graphene (TBG) with "magic-angle" (1.1°), where the electron-electron (e-e) interaction U becomes prominent relative to the small bandwidth W of the nearly flat band. However, the stringent requirement of this magic angle makes the sample preparation and the further application facing great challenges. Here, using scanning tunneling microscopy (STM) and spectroscopy (STS), we demonstrate that the correlation-induced symmetry-broken states can also be achieved in a 3.45° TBG, via engineering this nonmagic-angle TBG into regimes of U/W > 1. We enhance the e-e interaction through controlling the microscopic dielectric environment by using a MoS2 substrate. Simultaneously, the width of the low-energy van Hove singularity (VHS) peak is reduced by enhancing the interlayer coupling via STM tip modulation. When partially filled, the VHS peak exhibits a giant splitting into two states flanked by the Fermi level and shows a symmetry-broken LDOS distribution with a stripy charge order, which confirms the existence of strong correlation effect in our 3.45° TBG. Our result demonstrates the feasibility of the study and application of the correlation physics in TBGs with a wider range of twist angle.
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Affiliation(s)
- Kaihui Li
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
| | - Long-Jing Yin
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Chenglong Che
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Shihao Zhang
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Xueying Liu
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
| | - Yulong Xiao
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
| | - Songlong Liu
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Qingjun Tong
- School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China
| | - Si-Yu Li
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
- Greater Bay Area Institute for Innovation, Hunan University, Guangzhou 511300, People's Republic of China
| | - Anlian Pan
- Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan Institute of Optoelectronic Integration and College of Materials Science and Engineering, Hunan University, Changsha 410082, People's Republic of China
- School of Physics and Electronics, Hunan Normal University, Changsha 410081, People's Republic of China
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26
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Liu Q, Feng N, Zou Y, Fan C, Wang J. Exploring the impact of stress on the electronic structure and optical properties of graphdiyne nanoribbons for advanced optoelectronic applications. Sci Rep 2024; 14:6051. [PMID: 38480809 PMCID: PMC10937923 DOI: 10.1038/s41598-024-56380-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2024] [Accepted: 03/05/2024] [Indexed: 03/17/2024] Open
Abstract
Graphdiyne (GDY), a two-dimensional carbon material with sp- and sp2-hybridization, is recognized for its unique electronic properties and well-dispersed porosity. Its versatility has led to its use in a variety of applications. The precise control of this material's properties is paramount for its effective utilization in nano-optical devices. One effective method of regulation, which circumvents the need for additional disturbances, involves the application of external stress. This technique provides a direct means of eliciting changes in the electronic characteristics of the material. For instance, when subjected to uniaxial stress, electron transfer occurs at the triple bond. This results in an armchair-edged graphdiyne nanoribbon (A(3)-GDYNR) with a planar width of 2.07 nm, which exhibits a subtle plasmon effect at 500 nm. Conversely, a zigzag-edged graphdiyne nanoribbon (Z(3)-GDYNR) with a planar width of 2.86 nm demonstrates a pronounced plasmon effect within the 250-1200 nm range. This finding suggests that the zigzag nanoribbon surpasses the armchair nanoribbon in terms of its plasmon effect. First principles calculations and ab initio molecular dynamics further confirmed that under applied stress Z(3)-GDYNR exhibits less deformation than A(3)-GDYNR, indicating superior stability. This work provides the necessary theoretical basis for understanding graphene nanoribbons (GDYNRs).
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Affiliation(s)
- Qiaohan Liu
- College of Science, Liaoning Petrochemical University, Fushun, 113001, China
| | - Naixing Feng
- Key Laboratory of Intelligent Computing and Signal Processing, and School of Electronic and Information Engineering, Anhui University, Hefei, 230601, China
| | - Yi Zou
- College of Science, Liaoning Petrochemical University, Fushun, 113001, China.
| | - Chuanqiang Fan
- College of Science, Liaoning Petrochemical University, Fushun, 113001, China.
| | - Jingang Wang
- College of Science, Liaoning Petrochemical University, Fushun, 113001, China.
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27
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Jiang Y, Wang H, Bao K, Liu Z, Wang J. Monolayer V_{2}MX_{4}: A New Family of Quantum Anomalous Hall Insulators. PHYSICAL REVIEW LETTERS 2024; 132:106602. [PMID: 38518306 DOI: 10.1103/physrevlett.132.106602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 10/18/2023] [Accepted: 02/09/2024] [Indexed: 03/24/2024]
Abstract
We theoretically propose that the van der Waals layered ternary transition metal chalcogenide V_{2}MX_{4} (M=W, Mo; X=S, Se) is a new family of quantum anomalous Hall insulators with sizable bulk gap and Chern number C=-1. The large topological gap originates from the deep band inversion between spin-up bands contributed by d_{xz}, d_{yz} orbitals of V and spin-down band from d_{z^{2}} orbital of M at the Fermi level. Remarkably, the Curie temperature of monolayer V_{2}MX_{4} is predicted to be much higher than that of monolayer MnBi_{2}Te_{4}. Furthermore, the thickness dependence of the Chern number for few multilayers shows interesting oscillating behavior. The general physics from the d orbitals here applies to a large class of ternary transition metal chalcogenide such as Ti_{2}WX_{4} with the space group P-42m. These interesting predictions, if realized experimentally, could greatly promote the research and application of topological quantum physics.
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Affiliation(s)
- Yadong Jiang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Huan Wang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Kejie Bao
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Zhaochen Liu
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
| | - Jing Wang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
- Institute for Nanoelectronic Devices and Quantum Computing, Zhangjiang Fudan International Innovation Center, Fudan University, Shanghai 200433, China
- Hefei National Laboratory, Hefei 230088, China
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28
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Wang J, Cheng F, Sun Y, Xu H, Cao L. Stacking engineering in layered homostructures: transitioning from 2D to 3D architectures. Phys Chem Chem Phys 2024; 26:7988-8012. [PMID: 38380525 DOI: 10.1039/d3cp04656g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2024]
Abstract
Artificial materials, characterized by their distinctive properties and customized functionalities, occupy a central role in a wide range of applications including electronics, spintronics, optoelectronics, catalysis, and energy storage. The emergence of atomically thin two-dimensional (2D) materials has driven the creation of artificial heterostructures, harnessing the potential of combining various 2D building blocks with complementary properties through the art of stacking engineering. The promising outcomes achieved for heterostructures have spurred an inquisitive exploration of homostructures, where identical 2D layers are precisely stacked. This perspective primarily focuses on the field of stacking engineering within layered homostructures, where precise control over translational or rotational degrees of freedom between vertically stacked planes or layers is paramount. In particular, we provide an overview of recent advancements in the stacking engineering applied to 2D homostructures. Additionally, we will shed light on research endeavors venturing into three-dimensional (3D) structures, which allow us to proactively address the limitations associated with artificial 2D homostructures. We anticipate that the breakthroughs in stacking engineering in 3D materials will provide valuable insights into the mechanisms governing stacking effects. Such advancements have the potential to unlock the full capability of artificial layered homostructures, propelling the future development of materials, physics, and device applications.
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Affiliation(s)
- Jiamin Wang
- Changchun Institute of Optics, Fine Mechanics & Physics (CIOMP), Chinese Academy of Sciences, Changchun 130033, P. R. China.
- University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Fang Cheng
- State Key Laboratory for Organic Electronics and Information Displays & Jiangsu Key Laboratory for Biosensors, Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts and Telecommunications, Nanjing 210023, P. R. China
| | - Yan Sun
- Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, P. R. China.
| | - Hai Xu
- Changchun Institute of Optics, Fine Mechanics & Physics (CIOMP), Chinese Academy of Sciences, Changchun 130033, P. R. China.
- University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100049, P. R. China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Liang Cao
- Anhui Key Laboratory of Low-Energy Quantum Materials and Devices, High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences, Hefei 230031, P. R. China.
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29
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Pendharkar M, Tran SJ, Zaborski G, Finney J, Sharpe AL, Kamat RV, Kalantre SS, Hocking M, Bittner NJ, Watanabe K, Taniguchi T, Pittenger B, Newcomb CJ, Kastner MA, Mannix AJ, Goldhaber-Gordon D. Torsional force microscopy of van der Waals moirés and atomic lattices. Proc Natl Acad Sci U S A 2024; 121:e2314083121. [PMID: 38427599 DOI: 10.1073/pnas.2314083121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 01/11/2024] [Indexed: 03/03/2024] Open
Abstract
In a stack of atomically thin van der Waals layers, introducing interlayer twist creates a moiré superlattice whose period is a function of twist angle. Changes in that twist angle of even hundredths of a degree can dramatically transform the system's electronic properties. Setting a precise and uniform twist angle for a stack remains difficult; hence, determining that twist angle and mapping its spatial variation is very important. Techniques have emerged to do this by imaging the moiré, but most of these require sophisticated infrastructure, time-consuming sample preparation beyond stack synthesis, or both. In this work, we show that torsional force microscopy (TFM), a scanning probe technique sensitive to dynamic friction, can reveal surface and shallow subsurface structure of van der Waals stacks on multiple length scales: the moirés formed between bi-layers of graphene and between graphene and hexagonal boron nitride (hBN) and also the atomic crystal lattices of graphene and hBN. In TFM, torsional motion of an Atomic Force Microscope (AFM) cantilever is monitored as it is actively driven at a torsional resonance while a feedback loop maintains contact at a set force with the sample surface. TFM works at room temperature in air, with no need for an electrical bias between the tip and the sample, making it applicable to a wide array of samples. It should enable determination of precise structural information including twist angles and strain in moiré superlattices and crystallographic orientation of van der Waals flakes to support predictable moiré heterostructure fabrication.
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Affiliation(s)
- Mihir Pendharkar
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
| | - Steven J Tran
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Physics, Stanford University, Stanford, CA 94305
| | - Gregory Zaborski
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
| | - Joe Finney
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Physics, Stanford University, Stanford, CA 94305
| | - Aaron L Sharpe
- Materials Physics Department, Sandia National Laboratories, Livermore, CA 94550
| | - Rupini V Kamat
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Physics, Stanford University, Stanford, CA 94305
| | - Sandesh S Kalantre
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Physics, Stanford University, Stanford, CA 94305
| | - Marisa Hocking
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
| | | | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | | | | | - Marc A Kastner
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Physics, Stanford University, Stanford, CA 94305
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Andrew J Mannix
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
| | - David Goldhaber-Gordon
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
- Department of Physics, Stanford University, Stanford, CA 94305
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30
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Zhang NJ, Lin JX, Chichinadze DV, Wang Y, Watanabe K, Taniguchi T, Fu L, Li JIA. Angle-resolved transport non-reciprocity and spontaneous symmetry breaking in twisted trilayer graphene. NATURE MATERIALS 2024; 23:356-362. [PMID: 38388731 DOI: 10.1038/s41563-024-01809-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 01/16/2024] [Indexed: 02/24/2024]
Abstract
The identification and characterization of spontaneous symmetry breaking is central to our understanding of strongly correlated two-dimensional materials. In this work, we utilize the angle-resolved measurements of transport non-reciprocity to investigate spontaneous symmetry breaking in twisted trilayer graphene. By analysing the angular dependence of non-reciprocity in both longitudinal and transverse channels, we are able to identify the symmetry axis associated with the underlying electronic order. We report that a hysteretic rotation in the mirror axis can be induced by thermal cycles and a large current bias, supporting the spontaneous breaking of rotational symmetry. Moreover, the onset of non-reciprocity with decreasing temperature coincides with the emergence of orbital ferromagnetism. Combined with the angular dependence of the superconducting diode effect, our findings uncover a direct link between rotational and time-reversal symmetry breaking. These symmetry requirements point towards exchange-driven instabilities in momentum space as a possible origin for transport non-reciprocity in twisted trilayer graphene.
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Affiliation(s)
| | - Jiang-Xiazi Lin
- Department of Physics, Brown University, Providence, RI, USA
| | | | - Yibang Wang
- Department of Physics, Brown University, Providence, RI, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - J I A Li
- Department of Physics, Brown University, Providence, RI, USA.
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31
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Fox C, Mao Y, Zhang X, Wang Y, Xiao J. Stacking Order Engineering of Two-Dimensional Materials and Device Applications. Chem Rev 2024; 124:1862-1898. [PMID: 38150266 DOI: 10.1021/acs.chemrev.3c00618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
Stacking orders in 2D van der Waals (vdW) materials dictate the relative sliding (lateral displacement) and twisting (rotation) between atomically thin layers. By altering the stacking order, many new ferroic, strongly correlated and topological orderings emerge with exotic electrical, optical and magnetic properties. Thanks to the weak vdW interlayer bonding, such highly flexible and energy-efficient stacking order engineering has transformed the design of quantum properties in 2D vdW materials, unleashing the potential for miniaturized high-performance device applications in electronics, spintronics, photonics, and surface chemistry. This Review provides a comprehensive overview of stacking order engineering in 2D vdW materials and their device applications, ranging from the typical fabrication and characterization methods to the novel physical properties and the emergent slidetronics and twistronics device prototyping. The main emphasis is on the critical role of stacking orders affecting the interlayer charge transfer, orbital coupling and flat band formation for the design of innovative materials with on-demand quantum properties and surface potentials. By demonstrating a correlation between the stacking configurations and device functionality, we highlight their implications for next-generation electronic, photonic and chemical energy conversion devices. We conclude with our perspective of this exciting field including challenges and opportunities for future stacking order engineering research.
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Affiliation(s)
- Carter Fox
- Department of Materials Science and Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Physics, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Yulu Mao
- Department of Electrical and Computer Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Xiang Zhang
- Faculty of Science, University of Hong Kong, Hong Kong, China
- Faculty of Engineering, University of Hong Kong, Hong Kong, China
| | - Ying Wang
- Department of Materials Science and Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Physics, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Electrical and Computer Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Jun Xiao
- Department of Materials Science and Engineering, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
- Department of Physics, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
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32
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Yao Q, Xue Y, Zhao B, Zhu Y, Li Z, Yang Z. Orbital-Selectivity-Induced Robust Quantum Anomalous Hall Effect in Hund's Metals MgFeP. NANO LETTERS 2024; 24:1563-1569. [PMID: 38262051 DOI: 10.1021/acs.nanolett.3c04098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2024]
Abstract
Ferromagnetic (FM) states with high Curie temperatures (Tc) and strong spin-orbit coupling (SOC) are indispensable for the long-sought room-temperature quantum anomalous Hall (QAH) effects. Here, we propose a two-dimensional (2D) iron-based monolayer MgFeP that exhibits a notably high FM Tc (about 1525 K) along with exceptional structural stabilities. The unique multiorbital nature in MgFeP, where localized d x 2 - y 2 and dxz/yz orbitals coexist with itinerant dxy and dz2 orbitals, renders the monolayer a Hund's metal and in an orbital-selective Mott phase (OSMP). This OSMP triggers an FM double exchange mechanism, rationalizing the high Tc in the Hund's metal. This material transitions to a QAH insulator upon consideration of the SOC effect. By leveraging orbital selectivity, the QAH band gap can be enlarged by more than two times (to 137 meV). Our findings showcase Hund's metals as a promising material platform for realizing high-performance quantum topological electronic devices.
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Affiliation(s)
- Qingzhao Yao
- State Key Laboratory of Surface Physics and Key Laboratory of Computational Physical Sciences (MOE) and Department of Physics, Fudan University, Shanghai 200433, China
- Shanghai Qi Zhi Institute, Shanghai 200030, China
| | - Yang Xue
- School of Physics, East China University of Science and Technology, Shanghai 200237, China
| | - Bao Zhao
- School of Physics Science and Information Technology, Liaocheng University, Liaocheng 252059, China
| | - Ye Zhu
- State Key Laboratory of Surface Physics and Key Laboratory of Computational Physical Sciences (MOE) and Department of Physics, Fudan University, Shanghai 200433, China
- Shanghai Qi Zhi Institute, Shanghai 200030, China
| | - Zhijian Li
- State Key Laboratory of Surface Physics and Key Laboratory of Computational Physical Sciences (MOE) and Department of Physics, Fudan University, Shanghai 200433, China
- Shanghai Qi Zhi Institute, Shanghai 200030, China
| | - Zhongqin Yang
- State Key Laboratory of Surface Physics and Key Laboratory of Computational Physical Sciences (MOE) and Department of Physics, Fudan University, Shanghai 200433, China
- Shanghai Qi Zhi Institute, Shanghai 200030, China
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33
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Lu X, Xie B, Yang Y, Zhang Y, Kong X, Li J, Ding F, Wang ZJ, Liu J. Magic Momenta and Three-Dimensional Landau Levels from a Three-Dimensional Graphite Moiré Superlattice. PHYSICAL REVIEW LETTERS 2024; 132:056601. [PMID: 38364175 DOI: 10.1103/physrevlett.132.056601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 11/17/2023] [Accepted: 01/04/2024] [Indexed: 02/18/2024]
Abstract
In this Letter, we theoretically explore the physical properties of a new type of three-dimensional graphite moiré superlattice, the bulk alternating twisted graphite (ATG) system with homogeneous twist angle, which is grown by in situ chemical vapor decomposition method. Compared to twisted bilayer graphene (TBG), the bulk ATG system is bestowed with an additional wave vector degree of freedom due to the extra dimensionality. As a result, when the twist angle of bulk ATG is smaller than twice of the magic angle of TBG, there always exist "magic momenta" which host topological flat bands with vanishing in-plane Fermi velocities. Most saliently, when the twist angle is relatively large, a dispersionless three-dimensional zeroth Landau level would emerge in the bulk ATG, which may give rise to robust three-dimensional quantum Hall effects and unusual quantum-Hall physics over a large range of twist angles.
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Affiliation(s)
- Xin Lu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
| | - Bo Xie
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
| | - Yue Yang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Yiwen Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
| | - Xiao Kong
- Institute of Technology for Carbon Neutrality, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
- Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China
| | - Jun Li
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
| | - Feng Ding
- Institute of Technology for Carbon Neutrality, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
- Faculty of Materials Science and Energy Engineering, Shenzhen University of Advanced Technology, Shenzhen, China
| | - Zhu-Jun Wang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
- Liaoning Academy of Materials, Shenyang 110167, China
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34
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Li T, Chen H, Wang K, Hao Y, Zhang L, Watanabe K, Taniguchi T, Hong X. Transport Anisotropy in One-Dimensional Graphene Superlattice in the High Kronig-Penney Potential Limit. PHYSICAL REVIEW LETTERS 2024; 132:056204. [PMID: 38364165 DOI: 10.1103/physrevlett.132.056204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 09/11/2023] [Accepted: 01/05/2024] [Indexed: 02/18/2024]
Abstract
One-dimensional graphene superlattice subjected to strong Kronig-Penney (KP) potential is promising for achieving the electron-lensing effect, while previous studies utilizing the modulated dielectric gates can only yield a moderate, spatially dispersed potential profile. Here, we realize high KP potential modulation of graphene via nanoscale ferroelectric domain gating. Graphene transistors are fabricated on PbZr_{0.2}Ti_{0.8}O_{3} back gates patterned with periodic, 100-200 nm wide stripe domains. Because of band reconstruction, the h-BN top gating induces satellite Dirac points in samples with current along the superlattice vector s[over ^], a feature absent in samples with current perpendicular to s[over ^]. The satellite Dirac point position scales with the superlattice period (L) as ∝L^{β}, with β=-1.18±0.06. These results can be well explained by the high KP potential scenario, with the Fermi velocity perpendicular to s[over ^] quenched to about 1% of that for pristine graphene. Our study presents a promising material platform for realizing electron supercollimation and investigating flat band phenomena.
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Affiliation(s)
- Tianlin Li
- Department of Physics and Astronomy and Nebraska Center of Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - Hanying Chen
- Department of Physics and Astronomy and Nebraska Center of Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - Kun Wang
- Department of Physics and Astronomy and Nebraska Center of Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - Yifei Hao
- Department of Physics and Astronomy and Nebraska Center of Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - Le Zhang
- Department of Physics and Astronomy and Nebraska Center of Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Xia Hong
- Department of Physics and Astronomy and Nebraska Center of Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
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35
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He M, Cai J, Zheng H, Seewald E, Taniguchi T, Watanabe K, Yan J, Yankowitz M, Pasupathy A, Yao W, Xu X. Dynamically tunable moiré exciton Rydberg states in a monolayer semiconductor on twisted bilayer graphene. NATURE MATERIALS 2024; 23:224-229. [PMID: 38177379 DOI: 10.1038/s41563-023-01713-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Accepted: 10/02/2023] [Indexed: 01/06/2024]
Abstract
Moiré excitons are emergent optical excitations in two-dimensional semiconductors with moiré superlattice potentials. Although these excitations have been observed on several platforms, a system with dynamically tunable moiré potential to tailor their properties is yet to be realized. Here we present a continuously tunable moiré potential in monolayer WSe2, enabled by its proximity to twisted bilayer graphene (TBG) near the magic angle. By tuning local charge density via gating, TBG provides a spatially varying and dynamically tunable dielectric superlattice for modulation of monolayer WSe2 exciton wave functions. We observed emergent moiré exciton Rydberg branches with increased energy splitting following doping of TBG due to exciton wave function hybridization between bright and dark Rydberg states. In addition, emergent Rydberg states can probe strongly correlated states in TBG at the magic angle. Our study provides a new platform for engineering moiré excitons and optical accessibility to electronic states with small correlation gaps in TBG.
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Affiliation(s)
- Minhao He
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Jiaqi Cai
- Department of Physics, University of Washington, Seattle, WA, USA
| | - Huiyuan Zheng
- Department of Physics, University of Hong Kong, Hong Kong, China
| | - Eric Seewald
- Department of Physics, Columbia University, New York, NY, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Jiaqiang Yan
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, USA
| | - Matthew Yankowitz
- Department of Physics, University of Washington, Seattle, WA, USA
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA
| | - Abhay Pasupathy
- Department of Physics, Columbia University, New York, NY, USA
| | - Wang Yao
- Department of Physics, University of Hong Kong, Hong Kong, China.
- HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China.
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, USA.
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36
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Han T, Lu Z, Scuri G, Sung J, Wang J, Han T, Watanabe K, Taniguchi T, Park H, Ju L. Correlated insulator and Chern insulators in pentalayer rhombohedral-stacked graphene. NATURE NANOTECHNOLOGY 2024; 19:181-187. [PMID: 37798567 DOI: 10.1038/s41565-023-01520-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 09/04/2023] [Indexed: 10/07/2023]
Abstract
Rhombohedral-stacked multilayer graphene hosts a pair of flat bands touching at zero energy, which should give rise to correlated electron phenomena that can be tuned further by an electric field. Moreover, when electron correlation breaks the isospin symmetry, the valley-dependent Berry phase at zero energy may give rise to topologically non-trivial states. Here we measure electron transport through hexagonal boron nitride-encapsulated pentalayer graphene down to 100 mK. We observed a correlated insulating state with resistance at the megaohm level or greater at charge density n = 0 and displacement field D = 0. Tight-binding calculations predict a metallic ground state under these conditions. By increasing D, we observed a Chern insulator state with C = -5 and two other states with C = -3 at a magnetic field of around 1 T. At high D and n, we observed isospin-polarized quarter- and half-metals. Hence, rhombohedral pentalayer graphene exhibits two different types of Fermi-surface instability, one driven by a pair of flat bands touching at zero energy, and one induced by the Stoner mechanism in a single flat band. Our results establish rhombohedral multilayer graphene as a suitable system for exploring intertwined electron correlation and topology phenomena in natural graphitic materials without the need for moiré superlattice engineering.
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Affiliation(s)
- Tonghang Han
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Zhengguang Lu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Giovanni Scuri
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Jiho Sung
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Jue Wang
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Tianyi Han
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Hongkun Park
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Long Ju
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
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37
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Lu Z, Han T, Yao Y, Reddy AP, Yang J, Seo J, Watanabe K, Taniguchi T, Fu L, Ju L. Fractional quantum anomalous Hall effect in multilayer graphene. Nature 2024; 626:759-764. [PMID: 38383622 DOI: 10.1038/s41586-023-07010-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2023] [Accepted: 12/21/2023] [Indexed: 02/23/2024]
Abstract
The fractional quantum anomalous Hall effect (FQAHE), the analogue of the fractional quantum Hall effect1 at zero magnetic field, is predicted to exist in topological flat bands under spontaneous time-reversal-symmetry breaking2-6. The demonstration of FQAHE could lead to non-Abelian anyons that form the basis of topological quantum computation7-9. So far, FQAHE has been observed only in twisted MoTe2 at a moiré filling factor v > 1/2 (refs. 10-13). Graphene-based moiré superlattices are believed to host FQAHE with the potential advantage of superior material quality and higher electron mobility. Here we report the observation of integer and fractional QAH effects in a rhombohedral pentalayer graphene-hBN moiré superlattice. At zero magnetic field, we observed plateaus of quantized Hall resistance [Formula: see text] at v = 1, 2/3, 3/5, 4/7, 4/9, 3/7 and 2/5 of the moiré superlattice, respectively, accompanied by clear dips in the longitudinal resistance Rxx. Rxy equals [Formula: see text] at v = 1/2 and varies linearly with v, similar to the composite Fermi liquid in the half-filled lowest Landau level at high magnetic fields14-16. By tuning the gate-displacement field D and v, we observed phase transitions from composite Fermi liquid and FQAH states to other correlated electron states. Our system provides an ideal platform for exploring charge fractionalization and (non-Abelian) anyonic braiding at zero magnetic field7-9,17-19, especially considering a lateral junction between FQAHE and superconducting regions in the same device20-22.
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Affiliation(s)
- Zhengguang Lu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Tonghang Han
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Yuxuan Yao
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Aidan P Reddy
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Jixiang Yang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Junseok Seo
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Liang Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Long Ju
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
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38
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Bai Y, Li Y, Luan J, Liu R, Song W, Chen Y, Ji PF, Zhang Q, Meng F, Tong B, Li L, Jiang Y, Gao Z, Gu L, Zhang J, Wang Y, Xue QK, He K, Feng Y, Feng X. Quantized anomalous Hall resistivity achieved in molecular beam epitaxy-grown MnBi 2Te 4 thin films. Natl Sci Rev 2024; 11:nwad189. [PMID: 38213514 PMCID: PMC10776363 DOI: 10.1093/nsr/nwad189] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 04/29/2023] [Accepted: 05/16/2023] [Indexed: 01/13/2024] Open
Abstract
The intrinsic magnetic topological insulator MnBi2Te4 provides a feasible pathway to the high-temperature quantum anomalous Hall (QAH) effect as well as various novel topological quantum phases. Although quantized transport properties have been observed in exfoliated MnBi2Te4 thin flakes, it remains a big challenge to achieve molecular beam epitaxy (MBE)-grown MnBi2Te4 thin films even close to the quantized regime. In this work, we report the realization of quantized anomalous Hall resistivity in MBE-grown MnBi2Te4 thin films with the chemical potential tuned by both controlled in situ oxygen exposure and top gating. We find that elongated post-annealing obviously elevates the temperature to achieve quantization of the Hall resistivity, but also increases the residual longitudinal resistivity, indicating a picture of high-quality QAH puddles weakly coupled by tunnel barriers. These results help to clarify the puzzles in previous experimental studies on MnBi2Te4 and to find a way out of the big difficulty in obtaining MnBi2Te4 samples showing quantized transport properties.
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Affiliation(s)
- Yunhe Bai
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Yuanzhao Li
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Jianli Luan
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Ruixuan Liu
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Wenyu Song
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Yang Chen
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Peng-Fei Ji
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Qinghua Zhang
- Institute of Physics, Chinese Academy of Sciences, Beijing100190, China
| | - Fanqi Meng
- School of Materials Science and Engineering, Tsinghua University, Beijing100084, China
| | - Bingbing Tong
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
| | - Lin Li
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
| | - Yuying Jiang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
| | - Zongwei Gao
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
| | - Lin Gu
- School of Materials Science and Engineering, Tsinghua University, Beijing100084, China
| | - Jinsong Zhang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
- Frontier Science Center for Quantum Information, Beijing100084, China
- Hefei National Laboratory, Hefei230088, China
| | - Yayu Wang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
- Frontier Science Center for Quantum Information, Beijing100084, China
- Hefei National Laboratory, Hefei230088, China
| | - Qi-Kun Xue
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
- Frontier Science Center for Quantum Information, Beijing100084, China
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
- Southern University of Science and Technology, Shenzhen518055, China
| | - Ke He
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
- Frontier Science Center for Quantum Information, Beijing100084, China
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
- Hefei National Laboratory, Hefei230088, China
| | - Yang Feng
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
| | - Xiao Feng
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China
- Frontier Science Center for Quantum Information, Beijing100084, China
- Beijing Academy of Quantum Information Sciences, Beijing100193, China
- Hefei National Laboratory, Hefei230088, China
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39
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Xu R, Xu L, Liu Z, Yang L, Chen Y. ARPES investigation of the electronic structure and its evolution in magnetic topological insulator MnBi 2+2nTe 4+3n family. Natl Sci Rev 2024; 11:nwad313. [PMID: 38327664 PMCID: PMC10849349 DOI: 10.1093/nsr/nwad313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 11/14/2023] [Accepted: 11/19/2023] [Indexed: 02/09/2024] Open
Abstract
In the past 5 years, there has been significant research interest in the intrinsic magnetic topological insulator family compounds MnBi2+2nTe4+3n (where n = 0, 1, 2 …). In particular, exfoliated thin films of MnBi2Te4 have led to numerous experimental breakthroughs, such as the quantum anomalous Hall effect, axion insulator phase and high-Chern number quantum Hall effect without Landau levels. However, despite extensive efforts, the energy gap of the topological surface states due to exchange magnetic coupling, which is a key feature of the characteristic band structure of the system, remains experimentally elusive. The electronic structure measured by using angle-resolved photoemission (ARPES) shows significant deviation from ab initio prediction and scanning tunneling spectroscopy measurements, making it challenging to understand the transport results based on the electronic structure. This paper reviews the measurements of the band structure of MnBi2+2nTe4+3n magnetic topological insulators using ARPES, focusing on the evolution of their electronic structures with temperature, surface and bulk doping and film thickness. The aim of the review is to construct a unified picture of the electronic structure of MnBi2+2nTe4+3n compounds and explore possible control of their topological properties.
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Affiliation(s)
- Runzhe Xu
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
| | - Lixuan Xu
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- School of Physical Science and Technology, ShanghaiTech University and CAS-Shanghai Science Research Center, Shanghai 201210, China
| | - Zhongkai Liu
- School of Physical Science and Technology, ShanghaiTech University and CAS-Shanghai Science Research Center, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, Shanghai 200031, China
| | - Lexian Yang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
| | - Yulin Chen
- School of Physical Science and Technology, ShanghaiTech University and CAS-Shanghai Science Research Center, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, Shanghai 200031, China
- Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
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40
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Pandey V, Mishra S, Maity N, Paul S, B AM, Roy AK, Glavin NR, Watanabe K, Taniguchi T, Singh AK, Kochat V. Probing Interlayer Interactions and Commensurate-Incommensurate Transition in Twisted Bilayer Graphene through Raman Spectroscopy. ACS NANO 2024. [PMID: 38295130 DOI: 10.1021/acsnano.3c08344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2024]
Abstract
Twisted 2D layered materials have garnered much attention recently as a class of 2D materials whose interlayer interactions and electronic properties are dictated by the relative rotation/twist angle between the adjacent layers. In this work, we explore a prototype of such a twisted 2D system, artificially stacked twisted bilayer graphene (TBLG), where we probe, using Raman spectroscopy, the changes in the interlayer interactions and electron-phonon scattering pathways as the twist angle is varied from 0° to 30°. The long-range Moiré potential of the superlattice gives rise to additional intravalley and intervalley scattering of the electrons in TBLG, which has been investigated through their Raman signatures. Density functional theory (DFT) calculations of the electronic band structure of the TBLG superlattices were found to be in agreement with the resonant Raman excitations across the van Hove singularities in the valence and conduction bands predicted for TBLG due to hybridization of bands from the two layers. We also observe that the relative rotation between the graphene layers has a marked influence on the second order overtone and combination Raman modes signaling a commensurate-incommensurate transition in TBLG as the twist angle increases. This serves as a convenient and rapid characterization tool to determine the degree of commensurability in TBLG systems.
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Affiliation(s)
- Vineet Pandey
- Materials Science Centre, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
| | - Subhendu Mishra
- Materials Research Centre, Indian Institute of Science, Bengaluru 560012, India
| | - Nikhilesh Maity
- Materials Research Centre, Indian Institute of Science, Bengaluru 560012, India
| | - Sourav Paul
- Materials Science Centre, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
| | - Abhijith M B
- Materials Science Centre, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
| | - Ajit K Roy
- Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, United States
| | - Nicholas R Glavin
- Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, United States
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Abhishek K Singh
- Materials Research Centre, Indian Institute of Science, Bengaluru 560012, India
| | - Vidya Kochat
- Materials Science Centre, Indian Institute of Technology, Kharagpur, West Bengal 721302, India
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41
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Kuang X, Pantaleón Peralta PA, Angel Silva-Guillén J, Yuan S, Guinea F, Zhan Z. Optical properties and plasmons in moiré structures. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:173001. [PMID: 38232397 DOI: 10.1088/1361-648x/ad1f8c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Accepted: 01/17/2024] [Indexed: 01/19/2024]
Abstract
The discoveries of numerous exciting phenomena in twisted bilayer graphene (TBG) are stimulating significant investigations on moiré structures that possess a tunable moiré potential. Optical response can provide insights into the electronic structures and transport phenomena of non-twisted and twisted moiré structures. In this article, we review both experimental and theoretical studies of optical properties such as optical conductivity, dielectric function, non-linear optical response, and plasmons in moiré structures composed of graphene, hexagonal boron nitride (hBN), and/or transition metal dichalcogenides. Firstly, a comprehensive introduction to the widely employed methodology on optical properties is presented. After, moiré potential induced optical conductivity and plasmons in non-twisted structures are reviewed, such as single layer graphene-hBN, bilayer graphene-hBN and graphene-metal moiré heterostructures. Next, recent investigations of twist-angle dependent optical response and plasmons are addressed in twisted moiré structures. Additionally, we discuss how optical properties and plasmons could contribute to the understanding of the many-body effects and superconductivity observed in moiré structures.
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Affiliation(s)
- Xueheng Kuang
- Yangtze Delta Industrial Innovation Center of Quantum Science and Technology, Suzhou 215000, People's Republic of China
| | | | - Jose Angel Silva-Guillén
- Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
| | - Shengjun Yuan
- Key Laboratory of Artificial Micro- and Nano-structures of the Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, People's Republic of China
- Wuhan Institute of Quantum Technology, Wuhan 430206, People's Republic of China
| | - Francisco Guinea
- Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
- Donostia International Physics Center, Paseo Manuel de Lardizábal 4, 20018 San Sebastián, Spain
| | - Zhen Zhan
- Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain
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42
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Banerjee S, Scheurer MS. Enhanced Superconducting Diode Effect due to Coexisting Phases. PHYSICAL REVIEW LETTERS 2024; 132:046003. [PMID: 38335356 DOI: 10.1103/physrevlett.132.046003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 12/14/2023] [Indexed: 02/12/2024]
Abstract
The superconducting diode effect refers to an asymmetry in the critical supercurrent J_{c}(n[over ^]) along opposite directions, J_{c}(n[over ^])≠J_{c}(-n[over ^]). While the basic symmetry requirements for this effect are known, it is, for junction-free systems, difficult to capture within current theoretical models the large current asymmetries J_{c}(n[over ^])/J_{c}(-n[over ^]) recently observed in experiment. We here propose and develop a theory for an enhancement mechanism of the diode effect arising from spontaneous symmetry breaking. We show-both within a phenomenological and a microscopic theory-that there is a coupling of the supercurrent and the underlying symmetry-breaking order parameter. This coupling can enhance the current asymmetry significantly. Our work might not only provide a possible explanation for recent experiments on trilayer graphene but also pave the way for future realizations of the superconducting diode effect with large current asymmetries.
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Affiliation(s)
- Sayan Banerjee
- Institute for Theoretical Physics III, University of Stuttgart, 70550 Stuttgart, Germany and Institute for Theoretical Physics, University of Innsbruck, Innsbruck A-6020, Austria
| | - Mathias S Scheurer
- Institute for Theoretical Physics III, University of Stuttgart, 70550 Stuttgart, Germany and Institute for Theoretical Physics, University of Innsbruck, Innsbruck A-6020, Austria
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43
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Alhassan A, Yu M. Insight into the stacking effect on shifted patterns of bilayer phosphorene: a comprehensive first-principles study. NANOTECHNOLOGY 2024; 35:155701. [PMID: 38198734 DOI: 10.1088/1361-6528/ad1d14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 01/10/2024] [Indexed: 01/12/2024]
Abstract
It is crucial to deeply understand how the interlayer interaction acts on controlling the structural and electronic properties of shifted patterns of bilayer phosphorene. A comprehensive first-principles study on the bilayer phosphorene through relative translation along different directions has revealed that there is a direct correlation between the potential energy surface and the interlayer equilibrium distance. The shorter the interlayer distance, the lower the potential energy surface. The shifted patterns with the most stable state, the metastable state, and the transition state (with energy barrier of ∼1.3 meV/atom) were found associated with the AB, the Aδ, and the TS stacking configurations, respectively. The high energy barriers, on the other hand, are ∼9.3 meV/atom at the AA stacking configuration along the zigzag pathway, ∼5.3 meV/atom at the AB' stacking configuration along the armchair pathway, and ∼11.2 meV/atom at the AA' stacking configuration along the diagonal pathway, respectively. The character of electronic bandgap with respect to the shifting shows an anisotropic behavior (with the value of 0.69-1.22 eV). A transition from the indirect to the direct bandgap occurs under the shifting, implying a tunable bandgap by stacking engineering. Furthermore, the orbital hybridization at the interfacial region induces a redistribution of the net charge (∼0.002-0.011e) associated with the relative shifting between layers, leading to a strong polarization with stripe-like electron depletion near the lone pairs and accumulation in the middle of the interfacial region. It is expected that such interesting findings will provide a fundamental reference to deeply understand and analyze the complex local structural and electronic properties of twisted bilayer phosphorene and will make the shifted patterns of bilayer phosphorene promising for nanoelectronics as versatile shiftronics materials.
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Affiliation(s)
- Aswad Alhassan
- Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, United States of America
| | - Ming Yu
- Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, United States of America
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44
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Shayeganfar F, Ramazani A, Habibiyan H, Rafiee Diznab M. Terahertz linear/non-linear anomalous Hall conductivity of moiré TMD hetero-nanoribbons as topological valleytronics materials. Sci Rep 2024; 14:1581. [PMID: 38238394 PMCID: PMC10796390 DOI: 10.1038/s41598-024-51721-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Accepted: 01/09/2024] [Indexed: 01/22/2024] Open
Abstract
Twisted moiré van der Waals heterostructures hold promise to provide a robust quantum simulation platform for strongly correlated materials and realize elusive states of matter such as topological states in the laboratory. We demonstrated that the moiré bands of twisted transition metal dichalcogenide (TMD) hetero-nanoribbons exhibit non-trivial topological order due to the tendency of valence and conduction band states in K valleys to form giant band gaps when spin-orbit coupling (SOC) is taken into account. Among the features of twisted WS[Formula: see text]/MoS[Formula: see text] and WSe[Formula: see text]/MoSe[Formula: see text], we found that the heavy fermions associated with the topological flat bands and the presence of strongly correlated states, enhance anomalous Hall conductivity (AHC) away from the magic angle. By band analysis, we showed that the topmost conduction bands from the ± K-valleys are perfectly flat and carry a spin/valley Chern number. Moreover, we showed that the non-linear anomalous Hall effect in moiré TMD hetero-nanoribbons can be used to manipulate terahertz (THz) radiation. Our findings establish twisted heterostructures of group-VI TMD nanoribbons as a tunable platform for engineering topological valley quantum phases and THz non-linear Hall conductivity.
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Affiliation(s)
- Farzaneh Shayeganfar
- Department of Physics and Energy Engineering, Amirkabir University of Technology, Tehran, Iran.
| | - Ali Ramazani
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Hamidreza Habibiyan
- Department of Physics and Energy Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Mohammad Rafiee Diznab
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
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45
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Zou X, Li R, Chen Z, Dai Y, Huang B, Niu C. Engineering Gapless Edge States from Antiferromagnetic Chern Homobilayer. NANO LETTERS 2024; 24:450-457. [PMID: 38112315 DOI: 10.1021/acs.nanolett.3c04304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
We put forward that stacked Chern insulators with opposite chiralities offer a strategy to achieve gapless helical edge states in two dimensions. We employ the square lattice as an example and elucidate that the gapless chiral and helical edge states emerge in the monolayer and antiferromagnetically stacked bilayer, characterized by Chern number C = - 1 and spin Chern number C S = - 1 , respectively. Particularly, for a topological phase transition to the normal insulator in the stacked bilayer, a band gap closing and reopening procedure takes place accompanied by helical edge states disappearing, where the Chern insulating phase in the monolayer vanishes at the same time. Moreover, EuO is revealed as a suitable candidate for material realization. This work is not only valuable to the research of the quantum anomalous Hall effect but also offers a favorable platform to realize magnetic topologically insulating materials for spintronics applications.
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Affiliation(s)
- Xiaorong Zou
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
| | - Runhan Li
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
| | - Zhiqi Chen
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
| | - Ying Dai
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
| | - Baibiao Huang
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
| | - Chengwang Niu
- School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, Shandong 250100, China
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46
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Dettmann D, Sheverdyaeva PM, Hamzehpoor E, Franchi S, Galeotti G, Moras P, Ceccarelli C, Perepichka DF, Rosei F, Contini G. Electronic Band Engineering of Two-Dimensional Kagomé Polymers. ACS NANO 2024; 18:849-857. [PMID: 38147033 DOI: 10.1021/acsnano.3c09476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2023]
Abstract
Two-dimensional conjugated polymers (2DCPs) are an emerging class of materials that exhibit properties similar to graphene yet do not have the limitation of zero bandgap. On-surface synthesis provides exceptional control on the polymerization reaction, allowing tailoring properties by choosing suitable monomers. Heteroatom-substituted triangulene 2DCPs constitute a playing ground for such a design and are predicted to exhibit graphene-like band structures with high charge mobility and characteristic Dirac cones in conduction or valence states. However, measuring these properties experimentally is challenging and requires long-range-ordered polymers, preferably with an epitaxial relationship with the substrate. Here, we investigate the electronic properties of a mesoscale-ordered carbonyl-bridged triphenylamine 2DCP (P2TANGO) and demonstrate the presence of a Dirac cone by combining angle-resolved photoemission spectroscopy (ARPES) with density functional theory (DFT) calculations. Moreover, we measure the absolute energy position of the Dirac cone with respect to the vacuum level. We show that the bridging functionality of the triangulene (ether vs carbonyl) does not significantly perturb the band structure but strongly affects the positioning of the bands with respect to the Au(111) states and allows control of the ionization energy of the polymer. Our results provide proof of the controllable electronic properties of 2DCPs and bring us closer to their use in practical applications.
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Affiliation(s)
- Dominik Dettmann
- Centre Énergie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique Department, 1650 Boulevard Lionel-Boulet, J3X 1P7, Varennes, Québec, Canada
- Istituto di Struttura della Materia-CNR (ISM-CNR), Via Fosso del Cavaliere 100, 00133 Rome, Italy
| | - Polina M Sheverdyaeva
- Istituto di Struttura della Materia-CNR (ISM-CNR), Strada Statale 14 km 163.5, 34149, Trieste, Italy
| | - Ehsan Hamzehpoor
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, H3A 0B8, Montreal, Quebec, Canada
| | - Stefano Franchi
- Istituto di Struttura della Materia-CNR (ISM-CNR), Via Fosso del Cavaliere 100, 00133 Rome, Italy
| | - Gianluca Galeotti
- Centre Énergie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique Department, 1650 Boulevard Lionel-Boulet, J3X 1P7, Varennes, Québec, Canada
| | - Paolo Moras
- Istituto di Struttura della Materia-CNR (ISM-CNR), Strada Statale 14 km 163.5, 34149, Trieste, Italy
| | - Chiara Ceccarelli
- Istituto di Struttura della Materia-CNR (ISM-CNR), Via Fosso del Cavaliere 100, 00133 Rome, Italy
| | - Dmytro F Perepichka
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, H3A 0B8, Montreal, Quebec, Canada
| | - Federico Rosei
- Centre Énergie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique Department, 1650 Boulevard Lionel-Boulet, J3X 1P7, Varennes, Québec, Canada
| | - Giorgio Contini
- Istituto di Struttura della Materia-CNR (ISM-CNR), Via Fosso del Cavaliere 100, 00133 Rome, Italy
- Department of Physics, University Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
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47
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Moll PJW. All-electric writing of a chiral quantum memory. NATURE MATERIALS 2024; 23:35-36. [PMID: 38110513 DOI: 10.1038/s41563-023-01751-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2023]
Affiliation(s)
- Philip J W Moll
- Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany.
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48
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Scheer MG, Lian B. Twistronics of Kekulé Graphene: Honeycomb and Kagome Flat Bands. PHYSICAL REVIEW LETTERS 2023; 131:266501. [PMID: 38215385 DOI: 10.1103/physrevlett.131.266501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Accepted: 11/10/2023] [Indexed: 01/14/2024]
Abstract
Kekulé-O order in graphene, which has recently been realized experimentally, induces Dirac electron masses on the order of m∼100 meV. We show that twisted bilayer graphene in which one or both layers have Kekulé-O order exhibits nontrivial flat electronic bands on honeycomb and kagome lattices. When only one layer has Kekulé-O order, there is a parameter regime for which the lowest four bands at charge neutrality form an isolated two-orbital honeycomb lattice model with two flat bands. The bandwidths are minimal at a magic twist angle θ≈0.7° and Dirac mass m≈100 meV. When both layers have Kekulé-O order, there is a large parameter regime around θ≈1° and m≳100 meV in which the lowest three valence and conduction bands at charge neutrality each realize isolated kagome lattice models with one flat band, while the next three valence and conduction bands are flat bands on triangular lattices. These flat band systems may provide a new platform for strongly correlated phases of matter.
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Affiliation(s)
- Michael G Scheer
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Biao Lian
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
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49
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Chen H, Arora A, Song JCW, Loh KP. Gate-tunable anomalous Hall effect in Bernal tetralayer graphene. Nat Commun 2023; 14:7925. [PMID: 38040749 PMCID: PMC10692167 DOI: 10.1038/s41467-023-43796-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 11/20/2023] [Indexed: 12/03/2023] Open
Abstract
Large spin-orbit coupling is often thought to be critical in realizing magnetic order-locked charge transport such as the anomalous Hall effect (AHE). Recently, artificial stacks of two-dimensional materials, e.g., magic-angle twisted bilayer graphene on hexagonal boron-nitride heterostructures and dual-gated rhombohedral trilayer graphene, have become platforms for realizing AHE without spin-orbit coupling. However, these stacking arrangements are not energetically favorable, impeding experiments and further device engineering. Here we report an anomalous Hall effect in Bernal-stacked tetralayer graphene devices (BTG), the most stable configuration of four-layer graphene. BTG AHE is switched on by a displacement field and is most pronounced at low carrier densities. The onset of AHE occurs in tandem with a full metal to a broken isospin transition indicating an orbital origin of the itinerant ferromagnetism. At lowest densities, BTG exhibits an unconventional hysteresis with step-like anomalous Hall plateaus. Persisting to several tens of kelvin, AHE in BTG demonstrates the ubiquity and robustness of magnetic order in readily available and stable multilayer Bernal graphene stacks-a new venue for intrinsic non-reciprocal responses.
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Affiliation(s)
- Hao Chen
- Department of Chemistry, National University of Singapore, Singapore, Singapore
| | - Arpit Arora
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Justin C W Song
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
| | - Kian Ping Loh
- Department of Chemistry, National University of Singapore, Singapore, Singapore.
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50
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Yan X, Zheng Z, Sangwan VK, Qian JH, Wang X, Liu SE, Watanabe K, Taniguchi T, Xu SY, Jarillo-Herrero P, Ma Q, Hersam MC. Moiré synaptic transistor with room-temperature neuromorphic functionality. Nature 2023; 624:551-556. [PMID: 38123805 DOI: 10.1038/s41586-023-06791-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2023] [Accepted: 10/26/2023] [Indexed: 12/23/2023]
Abstract
Moiré quantum materials host exotic electronic phenomena through enhanced internal Coulomb interactions in twisted two-dimensional heterostructures1-4. When combined with the exceptionally high electrostatic control in atomically thin materials5-8, moiré heterostructures have the potential to enable next-generation electronic devices with unprecedented functionality. However, despite extensive exploration, moiré electronic phenomena have thus far been limited to impractically low cryogenic temperatures9-14, thus precluding real-world applications of moiré quantum materials. Here we report the experimental realization and room-temperature operation of a low-power (20 pW) moiré synaptic transistor based on an asymmetric bilayer graphene/hexagonal boron nitride moiré heterostructure. The asymmetric moiré potential gives rise to robust electronic ratchet states, which enable hysteretic, non-volatile injection of charge carriers that control the conductance of the device. The asymmetric gating in dual-gated moiré heterostructures realizes diverse biorealistic neuromorphic functionalities, such as reconfigurable synaptic responses, spatiotemporal-based tempotrons and Bienenstock-Cooper-Munro input-specific adaptation. In this manner, the moiré synaptic transistor enables efficient compute-in-memory designs and edge hardware accelerators for artificial intelligence and machine learning.
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Affiliation(s)
- Xiaodong Yan
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA
| | - Zhiren Zheng
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Vinod K Sangwan
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA
| | - Justin H Qian
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA
| | - Xueqiao Wang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Stephanie E Liu
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Material Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Su-Yang Xu
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
| | | | - Qiong Ma
- Department of Physics, Boston College, Chestnut Hill, MA, USA.
- CIFAR Azrieli Global Scholars Program, CIFAR, Toronto, Ontario, Canada.
| | - Mark C Hersam
- Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA.
- Department of Electrical and Computer Engineering, Northwestern University, Evanston, IL, USA.
- Department of Chemistry, Northwestern University, Evanston, IL, USA.
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