1
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Wei X, Tian C, Cui H, Zhai Y, Li Y, Liu S, Song Y, Feng Y, Huang M, Wang Z, Liu Y, Xiong Q, Yao Y, Xie XC, Chen JH. Three-dimensional hidden phase probed by in-plane magnetotransport in kagome metal CsV 3Sb 5 thin flakes. Nat Commun 2024; 15:5038. [PMID: 38866771 PMCID: PMC11169564 DOI: 10.1038/s41467-024-49248-3] [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: 05/09/2023] [Accepted: 05/27/2024] [Indexed: 06/14/2024] Open
Abstract
Transition metal compounds with kagome structure have been found to exhibit a variety of exotic structural, electronic, and magnetic orders. These orders are competing with energies very close to each other, resulting in complex phase transitions. Some of the phases are easily observable, such as the charge density wave (CDW) and the superconducting phase, while others are more challenging to identify and characterize. Here we present magneto-transport evidence of a new phase below ~ 35 K in the kagome topological metal CsV3Sb5 (CVS) thin flakes between the CDW and the superconducting transition temperatures. This phase is characterized by six-fold rotational symmetry in the in-plane magnetoresistance (MR) and is connected to the orbital current order in CVS. Furthermore, the phase is characterized by a large in-plane negative magnetoresistance, which suggests the existence of a three-dimensional, magnetic field-tunable orbital current ordered phase. Our results highlight the potential of magneto-transport to reveal the interactions between exotic quantum states of matter and to uncover the symmetry of such hidden phases.
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Affiliation(s)
- Xinjian Wei
- Beijing Academy of Quantum Information Sciences, Beijing, China
| | - Congkuan Tian
- Beijing Academy of Quantum Information Sciences, Beijing, China
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Hang Cui
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Yuxin Zhai
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, China
| | - Yongkai Li
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, School of Physics, Beijing Institute of Technology, Beijing, China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, China
- Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology, Jiaxing, China
| | - Shaobo Liu
- Beijing Academy of Quantum Information Sciences, Beijing, China
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Yuanjun Song
- Beijing Academy of Quantum Information Sciences, Beijing, China
| | - Ya Feng
- Beijing Academy of Quantum Information Sciences, Beijing, China
| | - Miaoling Huang
- Beijing Academy of Quantum Information Sciences, Beijing, China
| | - Zhiwei Wang
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, School of Physics, Beijing Institute of Technology, Beijing, China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, China
- Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology, Jiaxing, China
| | - Yi Liu
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing, China
| | - Qihua Xiong
- Beijing Academy of Quantum Information Sciences, Beijing, China
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, China
| | - Yugui Yao
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, School of Physics, Beijing Institute of Technology, Beijing, China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, China
- Material Science Center, Yangtze Delta Region Academy of Beijing Institute of Technology, Jiaxing, China
| | - X C Xie
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
- Hefei National Laboratory, Hefei, China
- Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China
| | - Jian-Hao Chen
- Beijing Academy of Quantum Information Sciences, Beijing, China.
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China.
- Hefei National Laboratory, Hefei, China.
- Key Laboratory for the Physics and Chemistry of Nanodevices, Peking University, Beijing, China.
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2
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Pu S, Balram AC, Taylor J, Fradkin E, Papić Z. Microscopic Model for Fractional Quantum Hall Nematics. PHYSICAL REVIEW LETTERS 2024; 132:236503. [PMID: 38905694 DOI: 10.1103/physrevlett.132.236503] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Accepted: 04/25/2024] [Indexed: 06/23/2024]
Abstract
Geometric fluctuations of the density mode in a fractional quantum Hall (FQH) state can give rise to a nematic FQH phase, a topological state with a spontaneously broken rotational symmetry. While experiments on FQH states in the second Landau level have reported signatures of putative FQH nematics in anisotropic transport, a realistic model for this state has been lacking. We show that the standard model of particles in the lowest Landau level interacting via the Coulomb potential realizes the FQH nematic transition, which is reached by a progressive reduction of the strength of the shortest-range Haldane pseudopotential. Using exact diagonalization and variational wave functions, we demonstrate that the FQH nematic transition occurs when the system's neutral gap closes in the long-wavelength limit while the charge gap remains open. We confirm the symmetry-breaking nature of the transition by demonstrating the existence of a "circular moat" potential in the manifold of states with broken rotational symmetry, while its geometric character is revealed through the strong fluctuations of the nematic susceptibility and Hall viscosity.
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Affiliation(s)
| | | | | | - Eduardo Fradkin
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA
- Anthony J. Leggett Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA
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3
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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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4
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Bigeard G, Cresti A. Magic-angle twisted bilayer graphene under orthogonal and in-plane magnetic fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:325502. [PMID: 38670079 DOI: 10.1088/1361-648x/ad4431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Accepted: 04/26/2024] [Indexed: 04/28/2024]
Abstract
We investigate the effect of a magnetic field on the band structure of bilayer graphene with a magic twist angle of 1.08∘. The coupling of a tight-binding model and the Peierls phase allows the calculation of the energy bands of periodic two-dimensional systems. For an orthogonal magnetic field, the Landau levels are dispersive, particularly for magnetic lengths comparable to or larger than the twisted bilayer cell size. A high in-plane magnetic field modifies the low-energy bands and gap, which we demonstrate to be a direct consequence of the minimal coupling.
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Affiliation(s)
- Gaëlle Bigeard
- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, CROMA, 38000 Grenoble, France
| | - Alessandro Cresti
- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, CROMA, 38000 Grenoble, France
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5
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Zhu X, Sun J, Feng S, Guo H. Moiré band renormalization due to lattice mismatch in bilayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:315502. [PMID: 38663420 DOI: 10.1088/1361-648x/ad43a3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Accepted: 04/25/2024] [Indexed: 05/08/2024]
Abstract
We investigated the band renormalization caused by the compressive-strain-induced lattice mismatch in parallel AA stacked bilayer graphene using two complementary methods: the tight-binding approach and the low-energy continuum theory. While a large mismatch does not alter the low-energy bands, a small one reduces the bandwidth of the low-energy bands along with a decrease in the Fermi velocity. In the tiny-mismatch regime, the low-energy continuum theory reveals that the long-period moiré pattern extensively renormalizes the low-energy bands, resulting in a significant reduction of bandwidth. Meanwhile, the Fermi velocity exhibits an oscillatory behavior and approaches zero at specific mismatches. However, the resulting low-energy bands are not perfectly isolated flat, as seen in twisted bilayer graphene at magic angles. These findings provide a deeper understanding of moiré physics and offer valuable guidance for related experimental studies in creating moiré superlattices using two-dimensional van der Waals heterostructures.
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Affiliation(s)
- Xingchuan Zhu
- Interdisciplinary Center for Fundamental and Frontier Sciences, Nanjing University of Science and Technology, Jiangyin, Jiangsu 214443, People's Republic of China
| | - Junsong Sun
- School of Physics, Beihang University, Beijing 100191, People's Republic of China
| | - Shiping Feng
- Department of Physics, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Huaiming Guo
- School of Physics, Beihang University, Beijing 100191, People's Republic of China
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6
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Fukushima K, Obata K, Yamane S, Hu Y, Li Y, Yao Y, Wang Z, Maeno Y, Yonezawa S. Violation of emergent rotational symmetry in the hexagonal Kagome superconductor CsV 3Sb 5. Nat Commun 2024; 15:2888. [PMID: 38605015 PMCID: PMC11009250 DOI: 10.1038/s41467-024-47043-8] [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: 02/02/2023] [Accepted: 03/12/2024] [Indexed: 04/13/2024] Open
Abstract
Superconductivity is caused by electron pairs that are canonically isotropic, whereas some exotic superconductors are known to exhibit non-trivial anisotropy stemming from unconventional pairings. However, superconductors with hexagonal symmetry, the highest rotational symmetry allowed in crystals, exceptionally have strong constraint that is called emergent rotational symmetry (ERS): anisotropic properties should be very weak especially near the critical temperature Tc even for unconventional pairings such as d-wave states. Here, we investigate superconducting anisotropy of the recently-found hexagonal Kagome superconductor CsV3Sb5, which is known to exhibit various intriguing phenomena originating from its undistorted Kagome lattice formed by vanadium atoms. Based on calorimetry performed under accurate two-axis field-direction control, we discover a combination of six- and two-fold anisotropies in the in-plane upper critical field. Both anisotropies, robust up to very close to Tc, are beyond predictions of standard theories. We infer that this clear ERS violation with nematicity is best explained by multi-component nematic superconducting order parameter in CsV3Sb5 intertwined with symmetry breakings caused by the underlying charge-density-wave order.
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Affiliation(s)
- Kazumi Fukushima
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
| | - Keito Obata
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
| | - Soichiro Yamane
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
- Department of Electronic Science and Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 615-8510, Japan
| | - Yajian Hu
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
| | - Yongkai Li
- Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Ministry of Education (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Material Science Center, Yangtze Delta Region Academy, Beijing Institute of Technology, Jiaxing, 314011, P. R. China
| | - Yugui Yao
- Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Ministry of Education (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, P. R. China
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, 100081, P. R. China
| | - Zhiwei Wang
- Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Ministry of Education (MOE), School of Physics, Beijing Institute of Technology, Beijing, 100081, P. R. China.
- Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing, 100081, P. R. China.
- Material Science Center, Yangtze Delta Region Academy, Beijing Institute of Technology, Jiaxing, 314011, P. R. China.
| | - Yoshiteru Maeno
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan
- Toyota Riken-Kyoto University Research Center (TRiKUC), Kyoto University, Kyoto, 606-8501, Japan
| | - Shingo Yonezawa
- Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan.
- Department of Electronic Science and Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 615-8510, Japan.
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7
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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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8
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Chen L, Teng X, Tan H, Winn BL, Granroth GE, Ye F, Yu DH, Mole RA, Gao B, Yan B, Yi M, Dai P. Competing itinerant and local spin interactions in kagome metal FeGe. Nat Commun 2024; 15:1918. [PMID: 38429271 PMCID: PMC10907581 DOI: 10.1038/s41467-023-44190-2] [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: 08/18/2023] [Accepted: 12/04/2023] [Indexed: 03/03/2024] Open
Abstract
The combination of a geometrically frustrated lattice, and similar energy scales between degrees of freedom endows two-dimensional Kagome metals with a rich array of quantum phases and renders them ideal for studying strong electron correlations and band topology. The Kagome metal, FeGe is a noted example of this, exhibiting A-type collinear antiferromagnetic (AFM) order at TN ≈ 400 K, then establishes a charge density wave (CDW) phase coupled with AFM ordered moment below TCDW ≈ 110 K, and finally forms a c-axis double cone AFM structure around TCanting ≈ 60 K. Here we use neutron scattering to demonstrate the presence of gapless incommensurate spin excitations associated with the double cone AFM structure of FeGe at temperatures well above TCanting and TCDW that merge into gapped commensurate spin waves from the A-type AFM order. Commensurate spin waves follow the Bose factor and fit the Heisenberg Hamiltonian, while the incommensurate spin excitations, emerging below TN where AFM order is commensurate, start to deviate from the Bose factor around TCDW, and peaks at TCanting. This is consistent with a critical scattering of a second order magnetic phase transition with decreasing temperature. By comparing these results with density functional theory calculations, we conclude that the incommensurate magnetic structure arises from the nested Fermi surfaces of itinerant electrons and the formation of a spin density wave order.
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Affiliation(s)
- Lebing Chen
- Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA
| | - Xiaokun Teng
- Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA
| | - Hengxin Tan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 7610001, Israel
| | - Barry L Winn
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Garrett E Granroth
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Feng Ye
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - D H Yu
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - R A Mole
- Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
| | - Bin Gao
- Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA
| | - Binghai Yan
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 7610001, Israel
| | - Ming Yi
- Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA
| | - Pengcheng Dai
- Department of Physics and Astronomy, Rice University, Houston, TX, 77005, USA.
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9
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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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10
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Poduval PP, Scheurer MS. Vestigial singlet pairing in a fluctuating magnetic triplet superconductor and its implications for graphene superlattices. Nat Commun 2024; 15:1713. [PMID: 38402211 PMCID: PMC10894192 DOI: 10.1038/s41467-024-45950-4] [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: 07/19/2023] [Accepted: 02/08/2024] [Indexed: 02/26/2024] Open
Abstract
Stacking and twisting graphene layers allows to create and control a two-dimensional electron liquid with strong correlations. Experiments indicate that these systems exhibit strong tendencies towards both magnetism and triplet superconductivity. Motivated by this phenomenology, we study a 2D model of fluctuating triplet pairing and spin magnetism. Individually, their respective order parameters, d and N, cannot order at finite temperature. Nonetheless, the model exhibits a variety of vestigial phases, including charge-4e superconductivity and broken time-reversal symmetry. Our main focus is on a phase characterized by finite d ⋅ N, which has the same symmetries as the BCS state, a Meissner effect, and metastable supercurrents, yet rather different spectral properties: most notably, the suppression of the electronic density of states at the Fermi level can resemble that of either a fully gapped or nodal superconductor, depending on parameters. This provides a possible explanation for recent tunneling experiments in the superconducting phase of graphene moiré systems.
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Affiliation(s)
- Prathyush P Poduval
- Donald Bren School of Information and Computer Sciences, University of California, Irvine, CA, 92697, USA.
- Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, MD, 20742, USA.
| | - Mathias S Scheurer
- Institute for Theoretical Physics III, University of Stuttgart, 70550, Stuttgart, Germany.
- Institute for Theoretical Physics, University of Innsbruck, Innsbruck, A-6020, Austria.
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11
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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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12
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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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13
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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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14
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Liu YB, Zhou J, Wu C, Yang F. Charge-4e superconductivity and chiral metal in 45°-twisted bilayer cuprates and related bilayers. Nat Commun 2023; 14:7926. [PMID: 38040764 PMCID: PMC10692084 DOI: 10.1038/s41467-023-43782-2] [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
The material realization of charge-4e/6e superconductivity (SC) is a big challenge. Here, we propose to realize charge-4e SC in maximally-twisted homobilayers, such as 45∘-twisted bilayer cuprates and 30∘-twisted bilayer graphene, referred to as twist-bilayer quasicrystals (TB-QC). When each monolayer hosts a pairing state with the largest pairing angular momentum, previous studies have found that the second-order interlayer Josephson coupling would drive chiral topological SC (TSC) in the TB-QC. Here we propose that, above the Tc of the chiral TSC, either charge-4e SC or chiral metal can arise as vestigial phases, depending on the ordering of the total- and relative-pairing-phase fields of the two layers. Based on a thorough symmetry analysis to get the low-energy effective Hamiltonian, we conduct a combined renormalization-group and Monte-Carlo study and obtain the phase diagram, which includes the charge-4e SC and chiral metal phases.
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Affiliation(s)
- Yu-Bo Liu
- School of Physics, Beijing Institute of Technology, Beijing, 100081, China
| | - Jing Zhou
- Department of Science, Chongqing University of Posts and Telecommunications, Chongqing, 400065, China
- Institute for Advanced Sciences, Chongqing University of Posts and Telecommunications, Chongqing, 400065, China
| | - Congjun Wu
- Institute for Theoretical Sciences, WestLake University, 310024, Hangzhou, China
- New Cornerstone Science Laboratory, Department of Physics, School of Science, Westlake University, 310024, Hangzhou, China
- Key Laboratory for Quantum Materials of Zhejiang Province, Department of Physics, School of Science, Westlake University, Hangzhou, 310030, P. R. China
- Institute of Natural Sciences, Westlake Institute for Advanced Study, Hangzhou, 310024, P. R. China
| | - Fan Yang
- School of Physics, Beijing Institute of Technology, Beijing, 100081, China.
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15
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Hu H, Rai G, Crippa L, Herzog-Arbeitman J, Călugăru D, Wehling T, Sangiovanni G, Valentí R, Tsvelik AM, Bernevig BA. Symmetric Kondo Lattice States in Doped Strained Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2023; 131:166501. [PMID: 37925696 DOI: 10.1103/physrevlett.131.166501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 09/11/2023] [Indexed: 11/07/2023]
Abstract
We use the topological heavy fermion (THF) model and its Kondo lattice (KL) formulation to study the possibility of a symmetric Kondo (SK) state in twisted bilayer graphene. Via a large-N approximation, we find a SK state in the KL model at fillings ν=0,±1,±2 where a KL model can be constructed. In the SK state, all symmetries are preserved and the local moments are Kondo screened by the conduction electrons. At the mean-field level of the THF model at ν=0,±1,±2,±3 we also find a similar symmetric state that is adiabatically connected to the symmetric Kondo state. We study the stability of the symmetric state by comparing its energy with the ordered (symmetry-breaking) states found in [H. Hu et al., Phys. Rev. Lett. 131, 026502 (2023).PRLTAO0031-900710.1103/PhysRevLett.131.026502, Z.-D. Song and B. A. Bernevig, Phys. Rev. Lett. 129, 047601 (2022).PRLTAO0031-900710.1103/PhysRevLett.129.047601] and find the ordered states to have lower energy at ν=0,±1,±2. However, moving away from integer fillings by doping the light bands, our mean-field calculations find the energy difference between the ordered state and the symmetric state to be reduced, which suggests the loss of ordering and a tendency toward Kondo screening. In order to include many-body effects beyond the mean-field approximation, we also performed dynamical mean-field theory calculations on the THF model in the nonordered phase. The spin susceptibility follows a Curie behavior at ν=0,±1,±2 down to ∼2 K where the onset of screening of the local moment becomes visible. This hints to very low Kondo temperatures at these fillings, in agreement with the outcome of our mean-field calculations. At noninteger filling ν=±0.5,±0.8,±1.2 dynamical mean-field theory shows deviations from a 1/T susceptibility at much higher temperatures, suggesting a more effective screening of local moments with doping. Finally, we study the effect of a C_{3z}-rotational-symmetry-breaking strain via mean-field approaches and find that a symmetric phase (that only breaks C_{3z} symmetry) can be stabilized at sufficiently large strain at ν=0,±1,±2. Our results suggest that a symmetric Kondo phase is strongly suppressed at integer fillings, but could be stabilized either at noninteger fillings or by applying strain.
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Affiliation(s)
- Haoyu Hu
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Spain
| | - Gautam Rai
- I. Institute of Theoretical Physics, University of Hamburg, Notkestrasse 9, 22607 Hamburg, Germany
| | - Lorenzo Crippa
- Institut für Theoretische Physik und Astrophysik and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, 97074 Würzburg, Germany
| | | | - Dumitru Călugăru
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Tim Wehling
- I. Institute of Theoretical Physics, University of Hamburg, Notkestrasse 9, 22607 Hamburg, Germany
- The Hamburg Centre for Ultrafast Imaging, 22761 Hamburg, Germany
| | - Giorgio Sangiovanni
- Institut für Theoretische Physik und Astrophysik and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, 97074 Würzburg, Germany
| | - Roser Valentí
- Institut für Theoretische Physik, Goethe Universität Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany
| | - Alexei M Tsvelik
- Division of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
| | - B Andrei Bernevig
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Spain
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
- IKERBASQUE, Basque Foundation for Science, Bilbao 48009, Spain
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16
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Kim D, Pandey J, Jeong J, Cho W, Lee S, Cho S, Yang H. Phase Engineering of 2D Materials. Chem Rev 2023; 123:11230-11268. [PMID: 37589590 DOI: 10.1021/acs.chemrev.3c00132] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/18/2023]
Abstract
Polymorphic 2D materials allow structural and electronic phase engineering, which can be used to realize energy-efficient, cost-effective, and scalable device applications. The phase engineering covers not only conventional structural and metal-insulator transitions but also magnetic states, strongly correlated band structures, and topological phases in rich 2D materials. The methods used for the local phase engineering of 2D materials include various optical, geometrical, and chemical processes as well as traditional thermodynamic approaches. In this Review, we survey the precise manipulation of local phases and phase patterning of 2D materials, particularly with ideal and versatile phase interfaces for electronic and energy device applications. Polymorphic 2D materials and diverse quantum materials with their layered, vertical, and lateral geometries are discussed with an emphasis on the role and use of their phase interfaces. Various phase interfaces have demonstrated superior and unique performance in electronic and energy devices. The phase patterning leads to novel homo- and heterojunction structures of 2D materials with low-dimensional phase boundaries, which highlights their potential for technological breakthroughs in future electronic, quantum, and energy devices. Accordingly, we encourage researchers to investigate and exploit phase patterning in emerging 2D materials.
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Affiliation(s)
- Dohyun Kim
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
| | - Juhi Pandey
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
| | - Juyeong Jeong
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
| | - Woohyun Cho
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
| | - Seungyeon Lee
- Division of Chemical Engineering and Materials Science, Graduate Program in System Health Science and Engineering, Ewha Womans University, Seoul 03760, Korea
| | - Suyeon Cho
- Division of Chemical Engineering and Materials Science, Graduate Program in System Health Science and Engineering, Ewha Womans University, Seoul 03760, Korea
| | - Heejun Yang
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
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17
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Li Y, Wan Q, Xu N. Recent Advances in Moiré Superlattice Systems by Angle-Resolved Photoemission Spectroscopy. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023:e2305175. [PMID: 37689836 DOI: 10.1002/adma.202305175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 08/16/2023] [Indexed: 09/11/2023]
Abstract
The last decade has witnessed a flourish in 2D materials including graphene and transition metal dichalcogenides (TMDs) as atomic-scale Legos. Artificial moiré superlattices via stacking 2D materials with a twist angle and/or a lattice mismatch have recently become a fertile playground exhibiting a plethora of emergent properties beyond their building blocks. These rich quantum phenomena stem from their nontrivial electronic structures that are effectively tuned by the moiré periodicity. Modern angle-resolved photoemission spectroscopy (ARPES) can directly visualize electronic structures with decent momentum, energy, and spatial resolution, thus can provide enlightening insights into fundamental physics in moiré superlattice systems and guides for designing novel devices. In this review, first, a brief introduction is given on advanced ARPES techniques and basic ideas of band structures in a moiré superlattice system. Then ARPES research results of various moiré superlattice systems are highlighted, including graphene on substrates with small lattice mismatches, twisted graphene/TMD moiré systems, and high-order moiré superlattice systems. Finally, it discusses important questions that remain open, challenges in current experimental investigations, and presents an outlook on this field of research.
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Affiliation(s)
- Yiwei Li
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
| | - Qiang Wan
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
| | - Nan Xu
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
- Wuhan Institute of Quantum Technology, Wuhan, 430206, China
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18
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Gao Q, Dong J, Ledwith P, Parker D, Khalaf E. Untwisting Moiré Physics: Almost Ideal Bands and Fractional Chern Insulators in Periodically Strained Monolayer Graphene. PHYSICAL REVIEW LETTERS 2023; 131:096401. [PMID: 37721816 DOI: 10.1103/physrevlett.131.096401] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 07/19/2023] [Indexed: 09/20/2023]
Abstract
Moiré systems have emerged in recent years as a rich platform to study strong correlations. Here, we will propose a simple, experimentally feasible setup based on periodically strained graphene that reproduces several key aspects of twisted moiré heterostructures-but without introducing a twist. We consider a monolayer graphene sheet subject to a C_{2}-breaking periodic strain-induced pseudomagnetic field with period L_{M}≫a, along with a scalar potential of the same period. This system has almost ideal flat bands with valley-resolved Chern number ±1, where the deviation from ideal band geometry is analytically controlled and exponentially small in the dimensionless ratio (L_{M}/l_{B})^{2}, where l_{B} is the magnetic length corresponding to the maximum value of the pseudomagnetic field. Moreover, the scalar potential can tune the bandwidth far below the Coulomb scale, making this a very promising platform for strongly interacting topological phases. Using a combination of strong-coupling theory and self-consistent Hartree-Fock, we find quantum anomalous Hall states at integer fillings. At fractional filling, exact diagonaliztion reveals a fractional Chern insulator at parameters in the experimentally feasible range. Overall, we find that this system has larger interaction-induced gaps, smaller quasiparticle dispersion, and enhanced tunability compared to twisted graphene systems, even in their ideal limit.
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Affiliation(s)
- Qiang Gao
- Department of Physics, The University of Texas at Austin, Texas 78712, USA
| | - Junkai Dong
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Patrick Ledwith
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Daniel Parker
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Eslam Khalaf
- Department of Physics, The University of Texas at Austin, Texas 78712, USA
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19
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Sobral JA, Obernauer S, Turkel S, Pasupathy AN, Scheurer MS. Machine learning the microscopic form of nematic order in twisted double-bilayer graphene. Nat Commun 2023; 14:5012. [PMID: 37591848 PMCID: PMC10435506 DOI: 10.1038/s41467-023-40684-1] [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: 03/06/2023] [Accepted: 08/01/2023] [Indexed: 08/19/2023] Open
Abstract
Modern scanning probe techniques, such as scanning tunneling microscopy, provide access to a large amount of data encoding the underlying physics of quantum matter. In this work, we show how convolutional neural networks can be used to learn effective theoretical models from scanning tunneling microscopy data on correlated moiré superlattices. Moiré systems are particularly well suited for this task as their increased lattice constant provides access to intra-unit-cell physics, while their tunability allows for the collection of high-dimensional data sets from a single sample. Using electronic nematic order in twisted double-bilayer graphene as an example, we show that incorporating correlations between the local density of states at different energies allows convolutional neural networks not only to learn the microscopic nematic order parameter, but also to distinguish it from heterostrain. These results demonstrate that neural networks are a powerful method for investigating the microscopic details of correlated phenomena in moiré systems and beyond.
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Affiliation(s)
- João Augusto Sobral
- Institute for Theoretical Physics III, University of Stuttgart, 70550, Stuttgart, Germany.
- Institute for Theoretical Physics, University of Innsbruck, A-6020, Innsbruck, Austria.
| | - Stefan Obernauer
- Institute for Theoretical Physics, University of Innsbruck, A-6020, Innsbruck, Austria
| | - Simon Turkel
- Department of Physics, Columbia University, 10027, New York, NY, USA
| | - Abhay N Pasupathy
- Department of Physics, Columbia University, 10027, New York, NY, USA
- Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, 11973, Upton, NY, USA
| | - Mathias S Scheurer
- Institute for Theoretical Physics III, University of Stuttgart, 70550, Stuttgart, Germany
- Institute for Theoretical Physics, University of Innsbruck, A-6020, Innsbruck, Austria
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20
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Park J. Fine tuning an atomic mesh. Science 2023; 381:604-605. [PMID: 37561858 DOI: 10.1126/science.adj1420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
Controlling the angle in atomic meshes could result in quantum properties on demand.
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Affiliation(s)
- Jiwoong Park
- Department of Chemistry, Pritzker School of Molecular Engineering, and James Franck Institute, University of Chicago, Chicago, IL, USA
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21
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Kapfer M, Jessen BS, Eisele ME, Fu M, Danielsen DR, Darlington TP, Moore SL, Finney NR, Marchese A, Hsieh V, Majchrzak P, Jiang Z, Biswas D, Dudin P, Avila J, Watanabe K, Taniguchi T, Ulstrup S, Bøggild P, Schuck PJ, Basov DN, Hone J, Dean CR. Programming twist angle and strain profiles in 2D materials. Science 2023; 381:677-681. [PMID: 37561852 DOI: 10.1126/science.ade9995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Accepted: 06/21/2023] [Indexed: 08/12/2023]
Abstract
Moiré superlattices in twisted two-dimensional materials have generated tremendous excitement as a platform for achieving quantum properties on demand. However, the moiré pattern is highly sensitive to the interlayer atomic registry, and current assembly techniques suffer from imprecise control of the average twist angle, spatial inhomogeneity in the local twist angle, and distortions caused by random strain. We manipulated the moiré patterns in hetero- and homobilayers through in-plane bending of monolayer ribbons, using the tip of an atomic force microscope. This technique achieves continuous variation of twist angles with improved twist-angle homogeneity and reduced random strain, resulting in moiré patterns with tunable wavelength and ultralow disorder. Our results may enable detailed studies of ultralow-disorder moiré systems and the realization of precise strain-engineered devices.
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Affiliation(s)
- Maëlle Kapfer
- Department of Physics, Columbia University, New York, NY, USA
| | - Bjarke S Jessen
- Department of Physics, Columbia University, New York, NY, USA
| | - Megan E Eisele
- Department of Physics, Columbia University, New York, NY, USA
| | - Matthew Fu
- Department of Physics, Columbia University, New York, NY, USA
| | - Dorte R Danielsen
- Center for Nanostructured Graphene, Technical University of Denmark, DK-2800, Denmark
- DTU Physics, Technical University of Denmark, DK-2800, Denmark
| | - Thomas P Darlington
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Samuel L Moore
- Department of Physics, Columbia University, New York, NY, USA
| | - Nathan R Finney
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Ariane Marchese
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Valerie Hsieh
- Department of Physics, Columbia University, New York, NY, USA
| | - Paulina Majchrzak
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Zhihao Jiang
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Deepnarayan Biswas
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Pavel Dudin
- Synchrotron SOLEIL, Université Paris-Saclay, F-91192 Gif sur Yvette, France
| | - José Avila
- Synchrotron SOLEIL, Université Paris-Saclay, F-91192 Gif sur Yvette, France
| | - 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
| | - Søren Ulstrup
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - Peter Bøggild
- Center for Nanostructured Graphene, Technical University of Denmark, DK-2800, Denmark
- DTU Physics, Technical University of Denmark, DK-2800, Denmark
| | - P J Schuck
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Dmitri N Basov
- Department of Physics, Columbia University, New York, NY, USA
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Cory R Dean
- Department of Physics, Columbia University, New York, NY, USA
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22
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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, Mao J, Han ZV, Gan Z, Lu J. Chemical Potential Characterization of Symmetry-Breaking Phases in a Rhombohedral Trilayer Graphene. NANO LETTERS 2023; 23:6875-6882. [PMID: 37466217 DOI: 10.1021/acs.nanolett.3c01262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2023]
Abstract
Rhombohedral trilayer graphene has recently emerged as a natural flat-band platform for studying interaction-driven symmetry-breaking phases. The displacement field (D) can further flatten the band to enhance the density of states, thereby controlling the electronic correlation that tips the energy balance between spin and valley degrees of freedom. To characterize the energy competition, chemical potential measurement─a direct thermodynamic probe of Fermi surfaces─is highly demanding to be conducted under a constant D. In this work, we characterize D-dependent isospin flavor polarization, where electronic states with isospin degeneracies of one and two can be identified. We also developed a method to measure the chemical potential at a fixed D, allowing for the extraction of energy variation during phase transitions. Furthermore, symmetry breaking could also be invoked in Landau levels, manifesting as quantum Hall ferromagnetism. Our work opens more opportunities for the thermodynamic characterization of displacement-field tuned van der Waals heterostructures.
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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
| | - 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 Vitto 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
| | - 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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23
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Nuckolls KP, Lee RL, Oh M, Wong D, Soejima T, Hong JP, Călugăru D, Herzog-Arbeitman J, Bernevig BA, Watanabe K, Taniguchi T, Regnault N, Zaletel MP, Yazdani A. Quantum textures of the many-body wavefunctions in magic-angle graphene. Nature 2023; 620:525-532. [PMID: 37587297 DOI: 10.1038/s41586-023-06226-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2023] [Accepted: 05/16/2023] [Indexed: 08/18/2023]
Abstract
Interactions among electrons create novel many-body quantum phases of matter with wavefunctions that reflect electronic correlation effects, broken symmetries and collective excitations. Many quantum phases have been discovered in magic-angle twisted bilayer graphene (MATBG), including correlated insulating1, unconventional superconducting2-5 and magnetic topological6-9 phases. The lack of microscopic information10,11 of possible broken symmetries has hampered our understanding of these phases12-17. Here we use high-resolution scanning tunnelling microscopy to study the wavefunctions of the correlated phases in MATBG. The squares of the wavefunctions of gapped phases, including those of the correlated insulating, pseudogap and superconducting phases, show distinct broken-symmetry patterns with a √3 × √3 super-periodicity on the graphene atomic lattice that has a complex spatial dependence on the moiré scale. We introduce a symmetry-based analysis using a set of complex-valued local order parameters, which show intricate textures that distinguish the various correlated phases. We compare the observed quantum textures of the correlated insulators at fillings of ±2 electrons per moiré unit cell to those expected for proposed theoretical ground states. In typical MATBG devices, these textures closely match those of the proposed incommensurate Kekulé spiral order15, whereas in ultralow-strain samples, our data have local symmetries like those of a time-reversal symmetric intervalley coherent phase12. Moreover, the superconducting state of MATBG shows strong signatures of intervalley coherence, only distinguishable from those of the insulator with our phase-sensitive measurements.
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Affiliation(s)
- Kevin P Nuckolls
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Ryan L Lee
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Myungchul Oh
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Dillon Wong
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Tomohiro Soejima
- Department of Physics, University of California, Berkeley, CA, USA
| | - Jung Pyo Hong
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Dumitru Călugăru
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - Jonah Herzog-Arbeitman
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
| | - B Andrei Bernevig
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA
- Donostia International Physics Center, Donostia-San Sebastian, Spain
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - 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
| | - Nicolas Regnault
- Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France
| | - Michael P Zaletel
- Department of Physics, University of California, Berkeley, CA, USA
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Ali Yazdani
- Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ, USA.
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24
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Hu H, Bernevig BA, Tsvelik AM. Kondo Lattice Model of Magic-Angle Twisted-Bilayer Graphene: Hund's Rule, Local-Moment Fluctuations, and Low-Energy Effective Theory. PHYSICAL REVIEW LETTERS 2023; 131:026502. [PMID: 37505959 DOI: 10.1103/physrevlett.131.026502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2022] [Accepted: 06/13/2023] [Indexed: 07/30/2023]
Abstract
We apply a generalized Schrieffer-Wolff transformation to the extended Anderson-like topological heavy fermion (THF) model for the magic-angle (θ=1.05°) twisted bilayer graphene (MATBLG) [Phys. Rev. Lett. 129, 047601 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.047601], to obtain its Kondo lattice limit. In this limit localized f electrons on a triangular lattice interact with topological conduction c electrons. By solving the exact limit of the THF model, we show that the integer fillings ν=0,±1,±2 are controlled by the heavy f electrons, while ν=±3 is at the border of a phase transition between two f-electron fillings. For ν=0,±1,±2, we then calculate the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions between the f moments in the full model and analytically prove the SU(4) Hund's rule for the ground state which maintains that two f electrons fill the same valley-spin flavor. Our (ferromagnetic interactions in the) spin model dramatically differ from the usual Heisenberg antiferromagnetic interactions expected at strong coupling. We show the ground state in some limits can be found exactly by employing a positive semidefinite "bond-operators" method. We then compute the excitation spectrum of the f moments in the ordered ground state, prove the stability of the ground state favored by RKKY interactions, and discuss the properties of the Goldstone modes, the (reason for the accidental) degeneracy of (some of) the excitation modes, and the physics of their phase stiffness. We develop a low-energy effective theory for the f moments and obtain analytic expressions for the dispersion of the collective modes. We discuss the relevance of our results to the spin-entropy experiments in TBG.
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Affiliation(s)
- Haoyu Hu
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Spain
| | - B Andrei Bernevig
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Spain
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
- IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
| | - Alexei M Tsvelik
- Division of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
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25
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Sainz-Cruz H, Pantaleón PA, Phong VT, Jimeno-Pozo A, Guinea F. Junctions and Superconducting Symmetry in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2023; 131:016003. [PMID: 37478460 DOI: 10.1103/physrevlett.131.016003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 05/31/2023] [Indexed: 07/23/2023]
Abstract
Junctions provide a wealth of information on the symmetry of the order parameter of superconductors. We analyze junctions between a scanning tunneling microscope (STM) tip and superconducting twisted bilayer graphene (TBG) and TBG Josephson junctions (JJs). We compare superconducting phases that are even or odd under valley exchange (s- or f-wave). The critical current in mixed (s and f) JJs strongly depends on the angle between the junction and the lattice. In STM-TBG junctions, due to Andreev reflection, the f-wave leads to a prominent peak in subgap conductance, as seen in experiments.
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Affiliation(s)
| | | | - Võ Tiến Phong
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | | | - Francisco Guinea
- Imdea Nanoscience, Faraday 9, 28015 Madrid, Spain
- Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastian, Spain
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26
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Guo Y, Qiu D, Shao M, Song J, Wang Y, Xu M, Yang C, Li P, Liu H, Xiong J. Modulations in Superconductors: Probes of Underlying Physics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2209457. [PMID: 36504310 DOI: 10.1002/adma.202209457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 11/16/2022] [Indexed: 06/02/2023]
Abstract
The importance of modulations is elevated to an unprecedented level, due to the delicate conditions required to bring out exotic phenomena in quantum materials, such as topological materials, magnetic materials, and superconductors. Recently, state-of-the-art modulation techniques in material science, such as electric-double-layer transistor, piezoelectric-based strain apparatus, angle twisting, and nanofabrication, have been utilized in superconductors. They not only efficiently increase the tuning capability to the broader ranges but also extend the tuning dimensionality to unprecedented degrees of freedom, including quantum fluctuations of competing phases, electronic correlation, and phase coherence essential to global superconductivity. Here, for a comprehensive review, these techniques together with the established modulation methods, such as elemental substitution, annealing, and polarization-induced gating, are contextualized. Depending on the mechanism of each method, the modulations are categorized into stoichiometric manipulation, electrostatic gating, mechanical modulation, and geometrical design. Their recent advances are highlighted by applications in newly discovered superconductors, e.g., nickelates, Kagome metals, and magic-angle graphene. Overall, the review is to provide systematic modulations in emergent superconductors and serve as the coordinate for future investigations, which can stimulate researchers in superconductivity and other fields to perform various modulations toward a thorough understanding of quantum materials.
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Affiliation(s)
- Yehao Guo
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Dong Qiu
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Mingxin Shao
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Jingyan Song
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Yang Wang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Minyi Xu
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Chao Yang
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Peng Li
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
| | - Haiwen Liu
- Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Jie Xiong
- State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, China
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27
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Sukhachov PO, von Oppen F, Glazman LI. Andreev Reflection in Scanning Tunneling Spectroscopy of Unconventional Superconductors. PHYSICAL REVIEW LETTERS 2023; 130:216002. [PMID: 37295098 DOI: 10.1103/physrevlett.130.216002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Accepted: 05/02/2023] [Indexed: 06/12/2023]
Abstract
We evaluate the differential conductance measured in an STM setting at arbitrary electron transmission between STM tip and a 2D superconductor with arbitrary gap structure. Our analytical scattering theory accounts for Andreev reflections, which become prominent at larger transmissions. We show that this provides complementary information about the superconducting gap structure beyond the tunneling density of states, strongly facilitating the ability to extract the gap symmetry and its relation to the underlying crystalline lattice. We use the developed theory to discuss recent experimental results on superconductivity in twisted bilayer graphene.
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Affiliation(s)
- P O Sukhachov
- Department of Physics, Yale University, New Haven, Connecticut 06520, USA
| | - Felix von Oppen
- Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - L I Glazman
- Department of Physics, Yale University, New Haven, Connecticut 06520, USA
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28
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Papaj M, Lewandowski C. Probing correlated states with plasmons. SCIENCE ADVANCES 2023; 9:eadg3262. [PMID: 37126543 DOI: 10.1126/sciadv.adg3262] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Understanding the nature of strongly correlated states in flat-band materials (such as moiré heterostructures) is at the forefront of both experimental and theoretical pursuits. While magnetotransport, scanning probe, and optical techniques are often very successful in investigating the properties of the underlying order, the exact nature of the ground state often remains unknown. Here, we propose to leverage strong light-matter coupling present in the flat-band systems to gain insight through dynamical dielectric response into the structure of the many-body ground state. We argue that because of the enlargement of the effective lattice of the system arising from correlations, conventional long-range plasmon becomes "folded" to yield a multiband plasmon spectrum. We detail several mechanisms through which the structure of the plasmon spectrum and that of the dynamical dielectric response is susceptible to the underlying order, revealing valued insights such as the interaction-driven band gaps, spin-structure, and the order periodicity.
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Affiliation(s)
- Michał Papaj
- Department of Physics, University of California, Berkeley, CA 94720, USA
| | - Cyprian Lewandowski
- National High Magnetic Field Laboratory, Tallahassee, FL, 32310, USA
- Department of Physics, Florida State University, Tallahassee, FL 32306, USA
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29
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Huang DM, Wu X, Chang K, Hu H, Wang YL, Xu HQ, Zhang JJ. Strain Effects in Twisted Spiral Antimonene. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023:e2301326. [PMID: 37092560 DOI: 10.1002/advs.202301326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Revised: 12/12/2012] [Indexed: 05/03/2023]
Abstract
Van der Waals (vdW) layered materials exhibit fruitful novel physical properties. The energy band of such materials depends strongly on their structures, and a tremendous variation in their physical properties can be deduced from a tiny change in inter-layer spacing, twist angle, or in-plane strain. In this work, a kind of vdW layered material of spiral antimonene is constructed, and the strain effects in the material are studied. The spiral antimonene is grown on a germanium (Ge) substrate and is induced by a helical dislocation penetrating through few atomic-layers of antimonene (β-phase). The as-grown spiral is intrinsically strained, and the lattice distortion is found to be pinned around the dislocation. Both spontaneous inter-layer twist and in-plane anisotropic strain are observed in scanning tunneling microscope (STM) measurements. The strain in the spiral antimonene can be significantly modified by STM tip interaction, leading to a variation in the surface electronic density of states (DOS) and a large modification in the work function of up to a few hundreds of millielectron-volts (meV). Those strain effects are expected to have potential applications in building up novel piezoelectric devices.
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Affiliation(s)
- Ding-Ming Huang
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices and School of Electronics, Peking University, Beijing, 100871, China
- National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Xu Wu
- MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, School of Integrated Circuits and Electronics, Beijing Institute of Technology, Beijing, 100081, China
| | - Kai Chang
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China
| | - Hao Hu
- Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an, 710054, China
| | - Ye-Liang Wang
- MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, School of Integrated Circuits and Electronics, Beijing Institute of Technology, Beijing, 100081, China
| | - H Q Xu
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, China
- Beijing Key Laboratory of Quantum Devices, Key Laboratory for the Physics and Chemistry of Nanodevices and School of Electronics, Peking University, Beijing, 100871, China
| | - Jian-Jun Zhang
- National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
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30
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Qin T, Zhong R, Cao W, Shen S, Wen C, Qi Y, Yan S. Real-Space Observation of Unidirectional Charge Density Wave and Complex Structural Modulation in the Pnictide Superconductor Ba 1-xSr xNi 2As 2. NANO LETTERS 2023; 23:2958-2963. [PMID: 37011415 DOI: 10.1021/acs.nanolett.3c00323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Here we use low-temperature and variable-temperature scanning tunneling microscopy to study the pnictide superconductor, Ba1-xSrxNi2As2. In the low-temperature phase (triclinic phase) of BaNi2As2, we observe the unidirectional charge density wave (CDW) with Q = 1/3 on both the Ba and NiAs surfaces. On the NiAs surface of the triclinic BaNi2As2, there are structural-modulation-induced chain-like superstructures with distinct periodicities. In the high-temperature phase (tetragonal phase) of BaNi2As2, the NiAs surface appears as the periodic 1 × 2 superstructure. Interestingly, in the triclinic phase of Ba0.5Sr0.5Ni2As2, the unidirectional CDW is suppressed on both the Ba/Sr and NiAs surfaces, and the Sr substitution stabilizes the periodic 1 × 2 superstructure on the NiAs surface, which enhance the superconductivity in Ba0.5Sr0.5Ni2As2. Our results provide important microscopic insights for the interplay among the unidirectional CDW, structural modulation, and superconductivity in this class of pnictide superconductors.
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Affiliation(s)
- Tian Qin
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Ruixia Zhong
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Weizheng Cao
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Shiwei Shen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Chenhaoping Wen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Yanpeng Qi
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
- Shanghai Key Laboratory of High-Resolution Electron Microscopy, ShanghaiTech University, Shanghai 201210, China
| | - Shichao Yan
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
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31
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Sayyad S, Kitatani M, Vaezi A, Aoki H. Nematicity-enhanced superconductivity in systems with a non-Fermi liquid behavior. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:245605. [PMID: 36947888 DOI: 10.1088/1361-648x/acc6af] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 03/22/2023] [Indexed: 06/18/2023]
Abstract
We explore the interplay between nematicity (spontaneous breaking of the sixfold rotational symmetry), superconductivity, and non-Fermi liquid behavior in partially flat-band (PFB) models on the triangular lattice. A key result is that the nematicity (Pomeranchuk instability), which is driven by many-body effect and stronger in flat-band systems, enhances superconducting transition temperature in a systematic manner on theTcdome. There, a plausiblesx2+y2-dx2-y2-dxy-wave symmetry, in place of the conventionaldx2-y2-wave, governs the nematicity-enhanced pairing with a sharp rise in theTcdome on the filling axis. When the sixfold symmetry is spontaneously broken, the pairing interaction is shown to become stronger with more compact pairs in real space than when the symmetry is enforced. These are accompanied by a non-Fermi character of electrons in the PFBs with many-body interactions.
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Affiliation(s)
- Sharareh Sayyad
- University Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France
- Max Planck Institute for the Science of Light, Staudtstraße 2, 91058 Erlangen, Germany
| | - Motoharu Kitatani
- RIKEN Center for Emergent Matter Sciences (CEMS), Wako, Saitama 351-0198, Japan
- Department of Material Science, University of Hyogo, Ako, Hyogo 678-1297, Japan
| | - Abolhassan Vaezi
- Department of Physics, Sharif University of Technology, Tehran 14588-89694, Iran
| | - Hideo Aoki
- Department of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan
- Electronics and Photonics Research Institute, Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
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32
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Scammell HD, Scheurer MS. Tunable Superconductivity and Möbius Fermi Surfaces in an Inversion-Symmetric Twisted van der Waals Heterostructure. PHYSICAL REVIEW LETTERS 2023; 130:066001. [PMID: 36827571 DOI: 10.1103/physrevlett.130.066001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 01/11/2023] [Indexed: 06/18/2023]
Abstract
We theoretically study a moiré superlattice geometry consisting of mirror-symmetric twisted trilayer graphene surrounded by identical transition metal dichalcogenide layers. We show that this setup allows us to switch on or off and control the spin-orbit splitting of the Fermi surfaces via application of a perpendicular displacement field D_{0} and explore two manifestations of this control: first, we compute the evolution of superconducting pairing with D_{0}; this features a complex admixture of singlet and triplet pairing and, depending on the pairing state in the parent trilayer system, phase transitions between competing superconducting phases. Second, we reveal that, with application of D_{0}, the spin-orbit-induced spin textures exhibit vortices which lead to "Möbius fermi surfaces" in the interior of the Brillouin zone: diabatic electron trajectories, which are predicted to dominate quantum oscillation experiments, require encircling the Γ point twice, making their Möbius nature directly observable. Further, we show that the superconducting order parameter inherits the unconventional, Möbius spin textures. Our findings suggest that this system provides a promising experimental avenue for systematically studying the impact of spin-orbit coupling on the multitude of topological and correlated phases in near-magic-angle twisted trilayer graphene.
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Affiliation(s)
- Harley D Scammell
- School of Physics, the University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Mathias S Scheurer
- Institute for Theoretical Physics, University of Innsbruck, Innsbruck A-6020, Austria
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33
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Tian H, Gao X, Zhang Y, Che S, Xu T, Cheung P, Watanabe K, Taniguchi T, Randeria M, Zhang F, Lau CN, Bockrath MW. Evidence for Dirac flat band superconductivity enabled by quantum geometry. Nature 2023; 614:440-444. [PMID: 36792742 DOI: 10.1038/s41586-022-05576-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 11/18/2022] [Indexed: 02/17/2023]
Abstract
In a flat band superconductor, the charge carriers' group velocity vF is extremely slow. Superconductivity therein is particularly intriguing, being related to the long-standing mysteries of high-temperature superconductors1 and heavy-fermion systems2. Yet the emergence of superconductivity in flat bands would appear paradoxical, as a small vF in the conventional Bardeen-Cooper-Schrieffer theory implies vanishing coherence length, superfluid stiffness and critical current. Here, using twisted bilayer graphene3-7, we explore the profound effect of vanishingly small velocity in a superconducting Dirac flat band system8-13. Using Schwinger-limited non-linear transport studies14,15, we demonstrate an extremely slow normal state drift velocity vn ≈ 1,000 m s-1 for filling fraction ν between -1/2 and -3/4 of the moiré superlattice. In the superconducting state, the same velocity limit constitutes a new limiting mechanism for the critical current, analogous to a relativistic superfluid16. Importantly, our measurement of superfluid stiffness, which controls the superconductor's electrodynamic response, shows that it is not dominated by the kinetic energy but instead by the interaction-driven superconducting gap, consistent with recent theories on a quantum geometric contribution8-12. We find evidence for small Cooper pairs, characteristic of the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover17-19, with an unprecedented ratio of the superconducting transition temperature to the Fermi temperature exceeding unity and discuss how this arises for ultra-strong coupling superconductivity in ultra-flat Dirac bands.
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Affiliation(s)
- Haidong Tian
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Xueshi Gao
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Yuxin Zhang
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Shi Che
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Tianyi Xu
- Department of Physics, The University of Texas at Dallas, Richardson, TX, USA
| | - Patrick Cheung
- Department of Physics, The University of Texas at Dallas, Richardson, TX, 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
| | - Mohit Randeria
- Department of Physics, The Ohio State University, Columbus, OH, USA
| | - Fan Zhang
- Department of Physics, The University of Texas at Dallas, Richardson, TX, USA
| | - Chun Ning Lau
- Department of Physics, The Ohio State University, Columbus, OH, USA.
| | - Marc W Bockrath
- Department of Physics, The Ohio State University, Columbus, OH, USA.
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34
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Goodwin ZAH, Fal'ko VI. Moiré modulation of charge density waves. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:494001. [PMID: 36223792 DOI: 10.1088/1361-648x/ac99ca] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 10/12/2022] [Indexed: 06/16/2023]
Abstract
Here we investigate how charge density waves (CDWs), inherent to a monolayer, are effected by creating twisted van der Waals structures. Homobilayers of metallic transition metal dichalcogenides (TMDs), at small twist angles where there is significant atomic reconstruction, are utilised as an example to investigate the interplay between the moiré domain structure and CDWs of different periods. For3×3CDWs, there is no geometric constraint to prevent the CDWs from propagating throughout the moiré structure. Whereas for2×2CDWs, to ensure the CDWs in each layer have the most favourable interactions in the domains, the CDW phase must be destroyed in the connecting domain walls. For3×3CDWs with twist angles close to 180∘, moiré-scale triangular structures can form; while close to 0∘, moiré-scale dimer domains occur. The star-of-David CDW (13×13) is found to host CDWs in the domains only, since there is one low energy stacking configuration, similar to the2×2CDWs. These predictions are offered for experimental verification in twisted bilayer metallic TMDs which host CDWs, and we hope this will stimulate further research on the interplay between the moiré superlattice and CDW phases intrinsic to the comprising 2D materials.
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Affiliation(s)
- Zachary A H Goodwin
- National Graphene Institute, University of Manchester, Booth St. E., Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Vladimir I Fal'ko
- National Graphene Institute, University of Manchester, Booth St. E., Manchester M13 9PL, United Kingdom
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- Henry Royce Institute for Advanced Materials, University of Manchester, Manchester M13 9PL, United Kingdom
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35
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Wang G, Chen C, Beshiwork BA, Xu B, Dong Y, Lin B. Fast proton and water transport in ceramic membrane-based magic-angle graphene. WATER RESEARCH 2022; 225:119076. [PMID: 36155004 DOI: 10.1016/j.watres.2022.119076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 08/26/2022] [Accepted: 09/06/2022] [Indexed: 06/16/2023]
Abstract
Ceramic membranes for energy conversion and storage devices are essential for becoming carbon neutral due to low cost and high stability, but limited by slow proton and water transport. Meanwhile magic-angle graphene with unconventional superconductivity ushers in a new era, properties research of which are in infant stage, urgently longing for specific applications. Herein, we investigate the ionic-conductivity and water-transport properties of ceramic membrane-based magic-angle graphene by choosing proton and water as a proof-of-concept for the first time, discover the twist-angle tuned proton conduction and water transport in ceramic membrane-based magic-angle graphene, demonstrate the faster proton and water transport in magic-angle graphene than that in graphene, and construct an efficient device of protonic ceramic membrane fuel cell based upon the new fast proton-conducting materials of magic-angle graphene. The proton conduction and water transport in magic-angle graphene can be easily tuned by the twist angle, explained by the corresponding potential energy surface. The smaller the twist angle is, and the faster the proton transport is. The protonic migration energy barrier in magic-angle graphene is lower by about 50% than that in graphene. Additionally, the water transport properties in magic-angle graphene can be improved by tuning twist angles. The electrode with magic-angle graphene can provide higher performance of protonic ceramic membrane fuel cells. The present work opens the specific application of ceramic membrane-based magic-angle graphene as new proton-conducting and water-transport materials in energy and environment.
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Affiliation(s)
- Guoqing Wang
- School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
| | - Chen Chen
- School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
| | - Bayu Admasu Beshiwork
- School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
| | - Bo Xu
- Department of Physics, Laboratory of Computational Materials Physics, Jiangxi Normal University, Nanchang 330022, China
| | - Yingchao Dong
- Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education, MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
| | - Bin Lin
- School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China.
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36
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Liu X, Peng R, Sun Z, Liu J. Moiré Phonons in Magic-Angle Twisted Bilayer Graphene. NANO LETTERS 2022; 22:7791-7797. [PMID: 36170965 PMCID: PMC9562463 DOI: 10.1021/acs.nanolett.2c02010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 09/11/2022] [Indexed: 06/16/2023]
Abstract
Magic-angle twisted bilayer graphene (TBG) has attracted significant interest recently due to the discoveries of diverse correlated and topological states. In this work, we study the phonon properties in magic-angle TBG based on many-body classical potential and interatomic forces generated by a deep neural network trained with data from ab initio calculations. We have discovered a number of soft modes which can exhibit dipolar, quadrupolar, and octupolar vibrational patterns in real space, as well as some time-reversal breaking chiral phonon modes. We have further studied the phonon effects on the electronic structures by freezing certain soft phonon modes. We find that if a soft quadrupolar phonon mode is assumed to be frozen, the system would exhibit a charge order which is perfectly consistent with recent experiments. Moreover, once some low-frequency C2z-breaking modes get frozen, the Dirac points at the charge neutrality point would be gapped out, which provides an alternative perspective to the origin of correlated insulator state at charge neutrality point.
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Affiliation(s)
- Xiaoqian Liu
- School
of Physical Science and Technology, ShanghaiTech
University, Shanghai 201210, China
| | - Ran Peng
- School
of Physical Science and Technology, ShanghaiTech
University, Shanghai 201210, China
| | - Zhaoru Sun
- 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
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37
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Li Y, Zhang S, Chen F, Wei L, Zhang Z, Xiao H, Gao H, Chen M, Liang S, Pei D, Xu L, Watanabe K, Taniguchi T, Yang L, Miao F, Liu J, Cheng B, Wang M, Chen Y, Liu Z. Observation of Coexisting Dirac Bands and Moiré Flat Bands in Magic-Angle Twisted Trilayer Graphene. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2205996. [PMID: 36043946 DOI: 10.1002/adma.202205996] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 08/10/2022] [Indexed: 06/15/2023]
Abstract
Moiré superlattices that consist of two or more layers of 2D materials stacked together with a small twist angle have emerged as a tunable platform to realize various correlated and topological phases, such as Mott insulators, unconventional superconductivity, and quantum anomalous Hall effect. Recently, magic-angle twisted trilayer graphene (MATTG) has shown both robust superconductivity similar to magic-angle twisted bilayer graphene and other unique properties, including the Pauli-limit violating and re-entrant superconductivity. These rich properties are deeply rooted in its electronic structure under the influence of distinct moiré potential and mirror symmetry. Here, combining nanometer-scale spatially resolved angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, the as-yet unexplored band structure of MATTG near charge neutrality is systematically measured. These measurements reveal the coexistence of the distinct dispersive Dirac band with the emergent moiré flat band, showing nice agreement with the theoretical calculations. These results serve as a stepstone for further understanding of the unconventional superconductivity in MATTG.
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Affiliation(s)
- Yiwei Li
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- Institute for Advanced Studies, Wuhan University, Luojiashan Street, Wuhan, Hubei, 430072, P. R. China
| | - Shihao Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 200031, P. R. China
| | - Fanqiang Chen
- National Laboratory of Solid State Microstructures, School of Physics, Institute of Brain-Inspired Intelligence, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China
| | - Liyang Wei
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
| | - Zonglin Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
| | - Hanbo Xiao
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
| | - Han Gao
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
| | - Moyu Chen
- National Laboratory of Solid State Microstructures, School of Physics, Institute of Brain-Inspired Intelligence, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China
| | - Shijun Liang
- National Laboratory of Solid State Microstructures, School of Physics, Institute of Brain-Inspired Intelligence, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China
| | - Ding Pei
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 200031, P. R. China
| | - Lixuan Xu
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, P. R. China
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Lexian Yang
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, P. R. China
- Frontier Science Center for Quantum Information, Beijing, 100084, P. R. China
| | - Feng Miao
- National Laboratory of Solid State Microstructures, School of Physics, Institute of Brain-Inspired Intelligence, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, P. R. China
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 200031, P. R. China
| | - Bin Cheng
- Institute of Interdisciplinary Physical Sciences, School of Science, Nanjing University of Science and Technology, Nanjing, 210094, P. R. China
| | - Meixiao Wang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 200031, P. R. China
| | - Yulin Chen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 200031, P. R. China
- State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing, 100084, P. R. China
- Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU, UK
| | - Zhongkai Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, P. R. China
- ShanghaiTech Laboratory for Topological Physics, Shanghai, 200031, P. R. China
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38
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Călugăru D, Regnault N, Oh M, Nuckolls KP, Wong D, Lee RL, Yazdani A, Vafek O, Bernevig BA. Spectroscopy of Twisted Bilayer Graphene Correlated Insulators. PHYSICAL REVIEW LETTERS 2022; 129:117602. [PMID: 36154402 DOI: 10.1103/physrevlett.129.117602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Accepted: 07/13/2022] [Indexed: 06/16/2023]
Abstract
We analytically compute the scanning tunneling microscopy (STM) signatures of integer-filled correlated ground states of the magic angle twisted bilayer graphene (TBG) narrow bands. After experimentally validating the strong-coupling approach at ±4 electrons/moiré unit cell, we consider the spatial features of the STM signal for 14 different many-body correlated states and assess the possibility of Kekulé distortion (KD) emerging at the graphene lattice scale. Remarkably, we find that coupling the two opposite graphene valleys in the intervalley-coherent (IVC) TBG insulators does not always result in KD. As an example, we show that the Kramers IVC state and its nonchiral U(4) rotations do not exhibit any KD, while the time-reversal-symmetric IVC state does. Our results, obtained over a large range of energies and model parameters, show that the STM signal and Chern number of a state can be used to uniquely determine the nature of the TBG ground state.
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Affiliation(s)
- Dumitru Călugăru
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Nicolas Regnault
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Myungchul Oh
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Kevin P Nuckolls
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Dillon Wong
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Ryan L Lee
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Ali Yazdani
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Oskar Vafek
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
- Department of Physics, Florida State University, Tallahassee, Florida 32306, USA
| | - B Andrei Bernevig
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
- Donostia International Physics Center, P. Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Spain
- IKERBASQUE, Basque Foundation for Science, 48009 Bilbao, Spain
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39
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Tunable quantum criticalities in an isospin extended Hubbard model simulator. Nature 2022; 609:479-484. [PMID: 36104555 PMCID: PMC9477744 DOI: 10.1038/s41586-022-05106-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 07/13/2022] [Indexed: 12/01/2022]
Abstract
Studying strong electron correlations has been an essential driving force for pushing the frontiers of condensed matter physics. In particular, in the vicinity of correlation-driven quantum phase transitions (QPTs), quantum critical fluctuations of multiple degrees of freedom facilitate exotic many-body states and quantum critical behaviours beyond Landau's framework1. Recently, moiré heterostructures of van der Waals materials have been demonstrated as highly tunable quantum platforms for exploring fascinating, strongly correlated quantum physics2-22. Here we report the observation of tunable quantum criticalities in an experimental simulator of the extended Hubbard model with spin-valley isospins arising in chiral-stacked twisted double bilayer graphene (cTDBG). Scaling analysis shows a quantum two-stage criticality manifesting two distinct quantum critical points as the generalized Wigner crystal transits to a Fermi liquid by varying the displacement field, suggesting the emergence of a critical intermediate phase. The quantum two-stage criticality evolves into a quantum pseudo criticality as a high parallel magnetic field is applied. In such a pseudo criticality, we find that the quantum critical scaling is only valid above a critical temperature, indicating a weak first-order QPT therein. Our results demonstrate a highly tunable solid-state simulator with intricate interplay of multiple degrees of freedom for exploring exotic quantum critical states and behaviours.
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40
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Xu C, Ge C, Sun D, Fan Y, Wang XB. Boron nitride materials as emerging catalysts for oxidative dehydrogenation of light alkanes. NANOTECHNOLOGY 2022; 33:432003. [PMID: 35760042 DOI: 10.1088/1361-6528/ac7c23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 06/27/2022] [Indexed: 06/15/2023]
Abstract
Light olefins (C2-C4) play a crucial role as basic ingredients in chemical industry, and oxidative dehydrogenation (ODH) of light alkanes to olefins has been one of the popular routes since the shale gas revolution. ODH of light alkanes has advantages on energy-and-cost saving as compared with traditional direct dehydrogenation, but it is restricted by its overoxidation which results in the relatively low olefin selectivity. Boron nitride (BN), an interesting nanomaterial with an analogous structure to graphene, springs out and manifests the superior performance as advanced catalysts in ODH, greatly improving the olefin selectivity under high alkane conversion. In this review, we introduce BN nanomaterials in four dimensions together with typical methods of syntheses. Traditional catalysts for ODH are also referred as comparison on several indicators-olefin yields and preparation techniques, including the metal-based catalysts and the non-metal-based catalysts. We also surveyed the BN catalysts for ODH reaction in recent five years, focusing on the different dimensions of BN together with the synthetic routes accounting for the active sites and the catalytic ability. Finally, an outlook of the potential promotion on the design of BN-based catalysts and the possible routes for the exploration of BN-related catalytic mechanisms are proposed.
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Affiliation(s)
- Chenyang Xu
- National Laboratory of Solid State Microstructures (NLSSM), Collaborative Innovation Center of Advanced Microstructures, College of Engineering and Applied Sciences, Nanjing University (NJU), Nanjing, 210093, People's Republic of China
| | - Cong Ge
- National Laboratory of Solid State Microstructures (NLSSM), Collaborative Innovation Center of Advanced Microstructures, College of Engineering and Applied Sciences, Nanjing University (NJU), Nanjing, 210093, People's Republic of China
| | - Dandan Sun
- National Laboratory of Solid State Microstructures (NLSSM), Collaborative Innovation Center of Advanced Microstructures, College of Engineering and Applied Sciences, Nanjing University (NJU), Nanjing, 210093, People's Republic of China
| | - Yining Fan
- Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, People's Republic of China
| | - Xue-Bin Wang
- National Laboratory of Solid State Microstructures (NLSSM), Collaborative Innovation Center of Advanced Microstructures, College of Engineering and Applied Sciences, Nanjing University (NJU), Nanjing, 210093, People's Republic of China
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41
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Burg GW, Khalaf E, Wang Y, Watanabe K, Taniguchi T, Tutuc E. Emergence of correlations in alternating twist quadrilayer graphene. NATURE MATERIALS 2022; 21:884-889. [PMID: 35798944 DOI: 10.1038/s41563-022-01286-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
Alternating twist multilayer graphene (ATMG) has recently emerged as a family of moiré systems that share several fundamental properties with twisted bilayer graphene, and are expected to host similarly strong electron-electron interactions near the magic angle. Here, we study alternating twist quadrilayer graphene (ATQG) samples with twist angles of 1.96° and 1.52°, which are slightly removed from the magic angle of 1.68°. At the larger angle, we find signatures of correlated insulators only when the ATQG is hole doped, and no signatures of superconductivity, and for the smaller angle we find evidence of superconductivity, while signs of the correlated insulators weaken. Our results provide insight into the twist angle dependence of correlated phases in ATMG and shed light on the nature of correlations in the intermediate coupling regime at the edge of the magic angle range where dispersion and interaction are of the same order.
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Affiliation(s)
- G William Burg
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX, USA
| | - Eslam Khalaf
- Department of Physics, Harvard University, Cambridge, MA, USA
- Department of Physics, The University of Texas at Austin, Austin, TX, USA
| | - Yimeng Wang
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX, USA
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute of Materials Science, Ibaraki, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute of Materials Science, Ibaraki, Japan
| | - Emanuel Tutuc
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX, USA.
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42
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Park JM, Cao Y, Xia LQ, Sun S, Watanabe K, Taniguchi T, Jarillo-Herrero P. Robust superconductivity in magic-angle multilayer graphene family. NATURE MATERIALS 2022; 21:877-883. [PMID: 35798945 DOI: 10.1038/s41563-022-01287-1] [Citation(s) in RCA: 44] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Accepted: 05/10/2022] [Indexed: 06/15/2023]
Abstract
The discovery of correlated states and superconductivity in magic-angle twisted bilayer graphene (MATBG) established a new platform to explore interaction-driven and topological phenomena. However, despite multitudes of correlated phases observed in moiré systems, robust superconductivity appears the least common, found only in MATBG and more recently in magic-angle twisted trilayer graphene. Here we report the experimental realization of superconducting magic-angle twisted four-layer and five-layer graphene, hence establishing alternating twist magic-angle multilayer graphene as a robust family of moiré superconductors. This finding suggests that the flat bands shared by the members play a central role in the superconductivity. Our measurements in parallel magnetic fields, in particular the investigation of Pauli limit violation and spontaneous rotational symmetry breaking, reveal a clear distinction between the N = 2 and N > 2-layer structures, consistent with the difference between their orbital responses to magnetic fields. Our results expand the emergent family of moiré superconductors, providing new insight with potential implications for design of new superconducting materials platforms.
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Affiliation(s)
- Jeong Min Park
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Yuan Cao
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Li-Qiao Xia
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Shuwen Sun
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Japan
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43
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Quantum cascade of correlated phases in trigonally warped bilayer graphene. Nature 2022; 608:298-302. [PMID: 35948716 DOI: 10.1038/s41586-022-04937-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2021] [Accepted: 06/07/2022] [Indexed: 11/08/2022]
Abstract
Divergent density of states offers an opportunity to explore a wide variety of correlated electron physics. In the thinnest limit, this has been predicted and verified in the ultraflat bands of magic-angle twisted bilayer graphene1-5, the band touching points of few-layer rhombohedral graphite6-8 and the lightly doped rhombohedral trilayer graphene9-11. The simpler and seemingly better understood Bernal bilayer graphene is also susceptible to orbital magnetism at charge neutrality7 leading to layer antiferromagnetic states12 or quantum anomalous Hall states13. Here we report the observation of a cascade of correlated phases in the vicinity of electric-field-controlled Lifshitz transitions14,15 and van Hove singularities16 in Bernal bilayer graphene. We provide evidence for the observation of Stoner ferromagnets in the form of half and quarter metals10,11. Furthermore, we identify signatures consistent with a topologically non-trivial Wigner-Hall crystal17 at zero magnetic field and its transition to a trivial Wigner crystal, as well as two correlated metals whose behaviour deviates from that of standard Fermi liquids. Our results in this reproducible, tunable, simple system open up new horizons for studying strongly correlated electrons.
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44
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Lin H, Zhang Z, Zhang H, Lin KT, Wen X, Liang Y, Fu Y, Lau AKT, Ma T, Qiu CW, Jia B. Engineering van der Waals Materials for Advanced Metaphotonics. Chem Rev 2022; 122:15204-15355. [PMID: 35749269 DOI: 10.1021/acs.chemrev.2c00048] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.
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Affiliation(s)
- Han Lin
- School of Science, RMIT University, Melbourne, Victoria 3000, Australia.,The Australian Research Council (ARC) Industrial Transformation Training, Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - Zhenfang Zhang
- School of Textile Science and Engineering, Xi'an Polytechnic University, Xi'an 710048, China
| | - Huihui Zhang
- Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Keng-Te Lin
- School of Science, RMIT University, Melbourne, Victoria 3000, Australia
| | - Xiaoming Wen
- Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Yao Liang
- Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Yang Fu
- Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Alan Kin Tak Lau
- Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Tianyi Ma
- School of Science, RMIT University, Melbourne, Victoria 3000, Australia.,Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
| | - Cheng-Wei Qiu
- Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
| | - Baohua Jia
- School of Science, RMIT University, Melbourne, Victoria 3000, Australia.,The Australian Research Council (ARC) Industrial Transformation Training, Centre in Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, Victoria 3122, Australia.,Centre for Translational Atomaterials, School of Science, Computing and Engineering Technologies, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia
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45
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Zhang S, Lu X, Liu J. Correlated Insulators, Density Wave States, and Their Nonlinear Optical Response in Magic-Angle Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2022; 128:247402. [PMID: 35776443 DOI: 10.1103/physrevlett.128.247402] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 03/26/2022] [Accepted: 05/24/2022] [Indexed: 06/15/2023]
Abstract
The correlated insulator (CI) states and the recently discovered density wave (DW) states in magic-angle twisted bilayer graphene (TBG) have stimulated intense research interest. However, to date, the nature of these "featureless" correlated states with zero Chern numbers are still elusive and lack a characteristic experimental signature. Thus, an experimental probe to identify the characters of these featureless CI and DW states is urgently needed. In this Letter, we theoretically study the correlated insulators and density wave states at different integer and fractional fillings of the flat bands in magic-angle TBG based on extended unrestricted Hartree-Fock calculations including the Coulomb screening effects from the remote bands. We further investigate the nonlinear optical response of the various correlated states and find that the nonlinear optical conductivities can be used to identify the nature of these CI and DW states at most of the fillings. Therefore, we propose that a nonlinear optical response can serve as a promising experimental probe for unveiling the nature of the CI and DW states observed in magic-angle TBG.
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Affiliation(s)
- Shihao Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xin Lu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- Laboratoire de Physique des Solides, Université Paris-Sud, Université Paris Saclay, CNRS, UMR 8502, F-91405 Orsay Cedex, France
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 201210, China
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46
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Evidence for unconventional superconductivity in twisted trilayer graphene. Nature 2022; 606:494-500. [PMID: 35705819 DOI: 10.1038/s41586-022-04715-z] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 04/01/2022] [Indexed: 11/08/2022]
Abstract
Magic-angle twisted trilayer graphene (MATTG) has emerged as a moiré material that exhibits strong electronic correlations and unconventional superconductivity1,2. However, local spectroscopic studies of this system are still lacking. Here we perform high-resolution scanning tunnelling microscopy and spectroscopy of MATTG that reveal extensive regions of atomic reconstruction favouring mirror-symmetric stacking. In these regions, we observe symmetry-breaking electronic transitions and doping-dependent band-structure deformations similar to those in magic-angle bilayers, as expected theoretically given the commonality of flat bands3,4. Most notably in a density window spanning two to three holes per moiré unit cell, the spectroscopic signatures of superconductivity are manifest as pronounced dips in the tunnelling conductance at the Fermi level accompanied by coherence peaks that become gradually suppressed at elevated temperatures and magnetic fields. The observed evolution of the conductance with doping is consistent with a gate-tunable transition from a gapped superconductor to a nodal superconductor, which is theoretically compatible with a sharp transition from a Bardeen-Cooper-Schrieffer superconductor to a Bose-Einstein-condensation superconductor with a nodal order parameter. Within this doping window, we also detect peak-dip-hump structures that suggest that superconductivity is driven by strong coupling to bosonic modes of MATTG. Our results will enable further understanding of superconductivity and correlated states in graphene-based moiré structures beyond twisted bilayers5.
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Wang P, Wen Y, Zhao X, Zhai B, Du R, Cheng M, Liu Z, He J, Shi J. Controllable Synthesis Quadratic-Dependent Unsaturated Magnetoresistance of Two-Dimensional Nonlayered Fe 7S 8 with Robust Environmental Stability. ACS NANO 2022; 16:8301-8308. [PMID: 35467830 DOI: 10.1021/acsnano.2c02267] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Two-dimensional (2D) iron chalcogenides (FeX, X = S, Se, Te) are emerging as an appealing class of materials for a wide range of research topics, including electronics, spintronics, and catalysis. However, the controlled syntheses and intrinsic property explorations of such fascinating materials still remain daunting challenges, especially for 2D nonlayered Fe7S8 with mixed-valence states and high conductivity. Herein, we design a general and temperature-mediated chemical vapor deposition (CVD) approach to synthesize ultrathin and large-domain Fe7S8 nanosheets on mica substrates, with the thickness down to ∼4.4 nm (2 unit-cell). Significantly, we uncover a quadratic-dependent unsaturated magnetoresistance (MR) with out-of-plane anisotropy in 2D Fe7S8, thanks to its ultrahigh crystalline quality and high conductivity (∼2.7 × 105 S m-1 at room temperature and ∼1.7 × 106 S m-1 at 2 K). More interestingly, the CVD-synthesized 2D Fe7S8 nanosheets maintain robust environmental stability for more than 8 months. These results hereby lay solid foundations for synthesizing 2D nonlayered iron chalcogenides with mixed-valence states and exploring fascinating quantum phenomena.
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Affiliation(s)
- Peng Wang
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Yao Wen
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Xiaoxu Zhao
- School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Baoxing Zhai
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Ruofan Du
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Mo Cheng
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
| | - Zheng Liu
- School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Jun He
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China
| | - Jianping Shi
- The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
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Wagner G, Kwan YH, Bultinck N, Simon SH, Parameswaran SA. Global Phase Diagram of the Normal State of Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2022; 128:156401. [PMID: 35499897 DOI: 10.1103/physrevlett.128.156401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Accepted: 03/28/2022] [Indexed: 06/14/2023]
Abstract
We investigate the full doping and strain-dependent phase diagram of the normal state of magic-angle twisted bilayer graphene (TBG). Using comprehensive Hartree-Fock calculations, we show that at temperatures where superconductivity is absent the global phase structure can be understood based on the competition and coexistence between three types of intertwined orders: a fully symmetric phase, spatially uniform flavor-symmetry-breaking states, and an incommensurate Kekulé spiral (IKS) order. For small strain, the IKS phase, recently proposed as a candidate order at all nonzero integer fillings of the moiré unit cell, is found to be ubiquitous for noninteger doping as well. We demonstrate that the corresponding electronic compressibility and Fermi surface structure are consistent with the "cascade" physics and Landau fans observed experimentally. This suggests a unified picture of the phase diagram of TBG in terms of IKS order.
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Affiliation(s)
- Glenn Wagner
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
- Department of Physics, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Yves H Kwan
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Nick Bultinck
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
- Department of Physics, Ghent University, Krijgslaan 281, 9000 Gent, Belgium
| | - Steven H Simon
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
| | - S A Parameswaran
- Rudolf Peierls Centre for Theoretical Physics, Parks Road, Oxford OX1 3PU, United Kingdom
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Abstract
Our work shows a fascinating application of finite-momentum superconductivity, the supercurrent diode effect, which is being reported in a growing number of experiments. We show that, under external magnetic field, Cooper pairs can acquire finite momentum so that critical currents in the direction parallel and antiparallel to the Cooper pair momentum become unequal. When both inversion and time-reversal symmetries are broken, the critical current of a superconductor can be nonreciprocal. In this work, we show that, in certain classes of two-dimensional superconductors with antisymmetric spin–orbit coupling, Cooper pairs acquire a finite momentum upon the application of an in-plane magnetic field, and, as a result, critical currents in the direction parallel and antiparallel to the Cooper pair momentum become unequal. This supercurrent diode effect is also manifested in the polarity dependence of in-plane critical fields induced by a supercurrent. These nonreciprocal effects may be found in polar SrTiO3 film, few-layer MoTe2 in the Td phase, and twisted bilayer graphene in which the valley degree of freedom plays a role analogous to spin.
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Xu L, Duan W, Liu Y, Wang J, Zhao Y, Li H, Liu H, Liu D. Twist-angle-controlled neutral exciton annihilation in WS 2 homostructures. NANOSCALE 2022; 14:5537-5544. [PMID: 35343557 DOI: 10.1039/d2nr00195k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Exciton-exciton annihilation (EEA), as typical nonradiative recombination, plays an unpopular role in semiconductors. The nonradiative process significantly reduces the quantum yield of photoluminescence, which substantially inhibits the maximum efficiency of optoelectronic devices. Recently, laser irradiation, introducing defects and applying strain have become effective means to restrain EEA in two-dimensional (2D) transition metal dichalcogenides (TMDCs). However, these methods destroy the atomic structure of 2D materials and limit their practical applications. Fortunately, twisted structures are expected to validly suppress EEA through excellent interface quality. Here, we develop a non-destructive way to control EEA in WS2 homostructures by changing the interlayer twist angle, and systematically study the effect of interlayer twist angle on EEA, using fluorescence lifetime imaging measurement (FLIM) technology. Due to the large moiré potential at a small interlayer twist angle, the diffusion of excitons is hindered, and the EEA rate decreases from 1.01 × 10-1 cm2 s-1 in a 9° twisted WS2 homostructure to 4.26 × 10-2 cm2 s-1 in a 1° twisted WS2 homostructure. The results reveal the important role of the interlayer twist angle and EEA interaction in high photoluminescence quantum yield optoelectronic devices based on TMDC homostructures.
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Affiliation(s)
- Lujie Xu
- School of Instrument Science and Opto-Electronics Engineering, Beijing Information Science and Technology University, Beijing 100192, China.
| | - Wenrui Duan
- School of Instrument Science and Opto-Electronics Engineering, Beijing Information Science and Technology University, Beijing 100192, China.
| | - Yuanshuang Liu
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
| | - Jiangcai Wang
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
| | - Yuanxi Zhao
- School of Instrument Science and Opto-Electronics Engineering, Beijing Information Science and Technology University, Beijing 100192, China.
| | - Huanglong Li
- Department of Precision Instrument, Center for Brain Inspired Computing Research, Tsinghua University, Beijing, 100084, China
| | - Huan Liu
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
| | - Dameng Liu
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
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