1
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Seiler AM, Jacobsen N, Statz M, Fernandez N, Falorsi F, Watanabe K, Taniguchi T, Dong Z, Levitov LS, Weitz RT. Probing the tunable multi-cone band structure in Bernal bilayer graphene. Nat Commun 2024; 15:3133. [PMID: 38605052 PMCID: PMC11009389 DOI: 10.1038/s41467-024-47342-0] [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: 02/26/2024] [Accepted: 03/27/2024] [Indexed: 04/13/2024] Open
Abstract
Bernal bilayer graphene (BLG) offers a highly flexible platform for tuning the band structure, featuring two distinct regimes. One is a tunable band gap induced by large displacement fields. Another is a gapless metallic band occurring at low fields, featuring rich fine structure consisting of four linearly dispersing Dirac cones and van Hove singularities. Even though BLG has been extensively studied experimentally, the evidence of this band structure is still elusive, likely due to insufficient energy resolution. Here, we use Landau levels as markers of the energy dispersion and analyze the Landau level spectrum in a regime where the cyclotron orbits of electrons or holes in momentum space are small enough to resolve the distinct mini Dirac cones. We identify the presence of four Dirac cones and map out topological transitions induced by displacement field. By clarifying the low-energy properties of BLG bands, these findings provide a valuable addition to the toolkit for graphene electronics.
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Affiliation(s)
- Anna M Seiler
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen, Germany
| | - Nils Jacobsen
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen, Germany
| | - Martin Statz
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen, Germany
| | - Noelia Fernandez
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen, Germany
| | - Francesca Falorsi
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen, Germany
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Japan
| | - Zhiyu Dong
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Leonid S Levitov
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - R Thomas Weitz
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen, Germany.
- International Center for Advanced Studies of Energy Conversion (ICASEC), University of Göttingen, Göttingen, Germany.
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2
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Xin B, Zou K, Liu D, Li B, Dong H, Cheng Y, Liu H, Zou LJ, Luo F, Lu F, Wang WH. Electronic structures and quantum capacitance of twisted bilayer graphene with defects based on three-band tight-binding model. Phys Chem Chem Phys 2024; 26:9687-9696. [PMID: 38470341 DOI: 10.1039/d3cp05913h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2024]
Abstract
Twisted bilayer graphene (tBLG) with C vacancies would greatly improve the density of states (DOS) around the Fermi level (EF) and quantum capacitance; however, the single-band tight-binding model only considering pz orbitals cannot accurately capture the low-energy physics of tBLG with C vacancies. In this work, a three-band tight-binding model containing three p orbitals of C atoms is proposed to explore the modulation mechanism of C vacancies on the DOS and quantum capacitance of tBLG. We first obtain the hopping integral parameters of the three-band tight-binding model, and then explore the electronic structures and the quantum capacitance of tBLG at a twisting angle of θ = 1.47° under different C vacancy concentrations. The impurity states contributed by C atoms with dangling bonds located around the EF and the interlayer hopping interaction could induce band splitting of the impurity states. Therefore, compared with the quantum capacitance of pristine tBLG (∼18.82 μF cm-2) at zero bias, the quantum capacitance is improved to ∼172.76 μF cm-2 at zero bias, and the working window with relatively large quantum capacitance in the low-voltage range is broadened in tBLG with C vacancies due to the enhanced DOS around the EF. Moreover, the quantum capacitance of tBLG is further increased at zero bias with an increase of the C vacancy concentration induced by more impurity states. These findings not only provide a suitable multi-band tight-binding model to describe tBLG with C vacancies but also offer theoretical insight for designing electrode candidates for low-power consumption devices with improved quantum capacitance.
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Affiliation(s)
- Baojuan Xin
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
| | - Kaixin Zou
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
| | - Dayong Liu
- Department of Physics, School of Sciences, Nantong University, Nantong 226019, China
| | - Boyan Li
- National Institute of Clean-and-Low-Carbon Energy, and Beijing Engineering Research Center of Nano-structured Thin Film Solar Cells, Beijing 102211, China
| | - Hong Dong
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
| | - Yahui Cheng
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
| | - Hui Liu
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
| | - Liang-Jian Zou
- Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China
| | - Feng Luo
- School of Materials Science and Engineering, Nankai University, Tianjin 300350, China
| | - Feng Lu
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
| | - Wei-Hua Wang
- Department of Electronic Science and Engineering, and Tianjin Key Laboratory of Efficient Utilization of Solar Energy, Nankai University, Tianjin 300350, China.
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3
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Xypakis E, de Turris V, Gala F, Ruocco G, Leonetti M. Physics-informed deep neural network for image denoising. OPTICS EXPRESS 2023; 31:43838-43849. [PMID: 38178470 DOI: 10.1364/oe.504606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Accepted: 11/14/2023] [Indexed: 01/06/2024]
Abstract
Image enhancement deep neural networks (DNN) can improve signal to noise ratio or resolution of optically collected visual information. The literature reports a variety of approaches with varying effectiveness. All these algorithms rely on arbitrary data (the pixels' count-rate) normalization, making their performance strngly affected by dataset or user-specific data pre-manipulation. We developed a DNN algorithm capable to enhance images signal-to-noise surpassing previous algorithms. Our model stems from the nature of the photon detection process which is characterized by an inherently Poissonian statistics. Our algorithm is thus driven by distance between probability functions instead than relying on the sole count-rate, producing high performance results especially in high-dynamic-range images. Moreover, it does not require any arbitrary image renormalization other than the transformation of the camera's count-rate into photon-number.
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4
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Yang K, Gao X, Wang Y, Zhang T, Gao Y, Lu X, Zhang S, Liu J, Gu P, Luo Z, Zheng R, Cao S, Wang H, Sun X, Watanabe K, Taniguchi T, Li X, Zhang J, Dai X, Chen JH, Ye Y, Han Z. Unconventional correlated insulator in CrOCl-interfaced Bernal bilayer graphene. Nat Commun 2023; 14:2136. [PMID: 37059725 PMCID: PMC10104821 DOI: 10.1038/s41467-023-37769-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 03/30/2023] [Indexed: 04/16/2023] Open
Abstract
The realization of graphene gapped states with large on/off ratios over wide doping ranges remains challenging. Here, we investigate heterostructures based on Bernal-stacked bilayer graphene (BLG) atop few-layered CrOCl, exhibiting an over-1-GΩ-resistance insulating state in a widely accessible gate voltage range. The insulating state could be switched into a metallic state with an on/off ratio up to 107 by applying an in-plane electric field, heating, or gating. We tentatively associate the observed behavior to the formation of a surface state in CrOCl under vertical electric fields, promoting electron-electron (e-e) interactions in BLG via long-range Coulomb coupling. Consequently, at the charge neutrality point, a crossover from single particle insulating behavior to an unconventional correlated insulator is enabled, below an onset temperature. We demonstrate the application of the insulating state for the realization of a logic inverter operating at low temperatures. Our findings pave the way for future engineering of quantum electronic states based on interfacial charge coupling.
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Affiliation(s)
- Kaining Yang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, PR China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, PR China
| | - Xiang Gao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, PR China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, PR China
| | - Yaning Wang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
- School of Material Science and Engineering, University of Science and Technology of China, Anhui, China
| | - Tongyao Zhang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, PR China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, PR China
| | - Yuchen Gao
- Collaborative Innovation Center of Quantum Matter, Beijing, China
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing, China
| | - Xin Lu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China.
| | - Shihao Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai, China
| | - Pingfan Gu
- Collaborative Innovation Center of Quantum Matter, Beijing, China
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing, China
| | - Zhaoping Luo
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
| | - Runjie Zheng
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
| | - Shimin Cao
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China
- Beijing Academy of Quantum Information Sciences, Beijing, China
| | - Hanwen Wang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
| | - Xingdan Sun
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
| | - 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
| | - Xiuyan Li
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
| | - Jing Zhang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, PR China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, PR China
| | - Xi Dai
- Materials Department, University of California, Santa Barbara, CA, USA.
- Department of Physics, The Hongkong University of Science and Technology, Hong Kong, China.
| | - Jian-Hao Chen
- International Center for Quantum Materials, School of Physics, Peking University, Beijing, China.
- Beijing Academy of Quantum Information Sciences, Beijing, China.
- Key Laboratory for the Physics and Chemistry of Nanodevices, Peking University, Beijing, China.
- Hefei National Laboratory, Hefei, China.
| | - Yu Ye
- Collaborative Innovation Center of Quantum Matter, Beijing, China.
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing, China.
| | - Zheng Han
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, PR China.
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, PR China.
- Liaoning Academy of Materials, Shenyang, China.
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5
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Geisenhof FR, Winterer F, Seiler AM, Lenz J, Zhang F, Weitz RT. Impact of Electric Field Disorder on Broken-Symmetry States in Ultraclean Bilayer Graphene. NANO LETTERS 2022; 22:7378-7385. [PMID: 36113049 DOI: 10.1021/acs.nanolett.2c02119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Bilayer graphene (BLG) has multiple internal degrees of freedom and a constant density of states down to the charge neutrality point when trigonal warping is ignored. Consequently, it is susceptible to various competing ground states. However, a coherent experimental determination of the ground state has been challenging due to the interaction-disorder interplay. Here we present an extensive transport study in a series of dually gated freestanding BLG devices and identify the layer-antiferromagnet as the ground state with a continuous strength across all devices. This strength correlates with the width of the state in the electric field. We systematically identify electric-field disorder─spatial variations in the interlayer potential difference─as the main source responsible for the observations. Our results pinpoint for the first time the importance of electric-field disorder on spontaneous symmetry breaking in BLG and solve a long-standing debate on its ground state. The electric-field disorder should be universal to all 2D materials.
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Affiliation(s)
- Fabian R Geisenhof
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, Munich 80539, Germany
| | - Felix Winterer
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, Munich 80539, Germany
| | - Anna M Seiler
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, Munich 80539, Germany
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen 37077, Germany
| | - Jakob Lenz
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, Munich 80539, Germany
| | - Fan Zhang
- Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, United States
| | - R Thomas Weitz
- Physics of Nanosystems, Department of Physics, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, Munich 80539, Germany
- Center for Nanoscience (CeNS), Schellingstrasse 4, Munich 80799, Germany
- Munich Center for Quantum Science and Technology (MCQST), Schellingstrasse 4, Munich 80799, Germany
- 1st Physical Institute, Faculty of Physics, University of Göttingen, Friedrich-Hund-Platz 1, Göttingen 37077, Germany
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6
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Vangelidis I, Bellas DV, Suckow S, Dabos G, Castilla S, Koppens FHL, Ferrari AC, Pleros N, Lidorikis E. Unbiased Plasmonic-Assisted Integrated Graphene Photodetectors. ACS PHOTONICS 2022; 9:1992-2007. [PMID: 35726242 PMCID: PMC9204831 DOI: 10.1021/acsphotonics.2c00100] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Indexed: 05/10/2023]
Abstract
Photonic integrated circuits (PICs) for next-generation optical communication interconnects and all-optical signal processing require efficient (∼A/W) and fast (≥25 Gbs-1) light detection at low (<pJbit-1) power consumption, in devices compatible with Si processing, so that the monolithic integration of electro-optical materials and electronics can be achieved consistently at the wafer scale. Graphene-based photodetectors can meet these criteria, thanks to their broadband absorption, ultra-high mobility, ultra-fast electron interactions, and strong photothermoelectric effect. High responsivities (∼ 1 A/W), however, have only been demonstrated in biased configurations, which introduce dark current, noise, and power consumption, while unbiased schemes, with low noise and zero consumption, have remained in the ∼ 0.1 A/W regime. Here, we consider the unbiased asymmetric configuration and show that optimized plasmonic enhanced devices can reach for both transverse-electric and transverse-magnetic modes (at λ = 1550 nm), ∼A/W responsivity, and ∼ 100 GHz operation speed at zero power consumption. We validate the model and material parameters by simulating experimental devices and derive analytical expressions for the responsivity. Our comprehensive modeling paves the way for efficient, fast, and versatile optical detection in PICs with zero power consumption.
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Affiliation(s)
- Ioannis Vangelidis
- Department
of Materials Science and Engineering, University
of Ioannina, Ioannina 45110, Greece
| | - Dimitris V. Bellas
- Department
of Materials Science and Engineering, University
of Ioannina, Ioannina 45110, Greece
- Department
of Informatics, Center for Interdisciplinary Research and Innovation, Aristotle University of Thessaloniki, Thessaloniki 57001, Greece
| | - Stephan Suckow
- AMO
GmbH, Advanced Microelectronic Center Aachen (AMICA), Otto-Blumenthal-Strasse 25, Aachen 52074, Germany
| | - George Dabos
- Department
of Informatics, Center for Interdisciplinary Research and Innovation, Aristotle University of Thessaloniki, Thessaloniki 57001, Greece
| | - Sebastián Castilla
- ICFO
- Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain
| | - Frank H. L. Koppens
- ICFO
- Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain
- ICREA
- Institució Catalana de Recerca i Estudis Avançats, Barcelona 08010, Spain
| | - Andrea C. Ferrari
- Cambridge
Graphene Centre, University of Cambridge, Cambridge CB3 0FA, U.K.
| | - Nikos Pleros
- Department
of Informatics, Center for Interdisciplinary Research and Innovation, Aristotle University of Thessaloniki, Thessaloniki 57001, Greece
| | - Elefterios Lidorikis
- Department
of Materials Science and Engineering, University
of Ioannina, Ioannina 45110, Greece
- University
Research Center of Ioannina (URCI), Institute of Materials Science
and Computing, Ioannina 45110, Greece
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7
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Zhou H, Holleis L, Saito Y, Cohen L, Huynh W, Patterson CL, Yang F, Taniguchi T, Watanabe K, Young AF. Isospin magnetism and spin-polarized superconductivity in Bernal bilayer graphene. Science 2022; 375:774-778. [PMID: 35025604 DOI: 10.1126/science.abm8386] [Citation(s) in RCA: 41] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
In conventional superconductors, Cooper pairing occurs between electrons of opposite spin. We observe spin-polarized superconductivity in Bernal bilayer graphene when doped to a saddle-point van Hove singularity generated by a large applied perpendicular electric field. We observe a cascade of electrostatic gate-tuned transitions between electronic phases distinguished by their polarization within the isospin space defined by the combination of the spin and momentum-space valley degrees of freedom. Although all of these phases are metallic at zero magnetic field, we observe a transition to a superconducting state at finite magnetic field B‖ ≈ 150 milliteslas applied parallel to the two-dimensional sheet. Superconductivity occurs near a symmetry-breaking transition and exists exclusively above the B‖ limit expected of a paramagnetic superconductor with the observed transition critical temperature TC ≈ 30 millikelvins, consistent with a spin-triplet order parameter.
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Affiliation(s)
- Haoxin Zhou
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Ludwig Holleis
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Yu Saito
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Liam Cohen
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - William Huynh
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Caitlin L Patterson
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Fangyuan Yang
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Andrea F Young
- Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
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8
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Ghazaryan A, Holder T, Serbyn M, Berg E. Unconventional Superconductivity in Systems with Annular Fermi Surfaces: Application to Rhombohedral Trilayer Graphene. PHYSICAL REVIEW LETTERS 2021; 127:247001. [PMID: 34951779 DOI: 10.1103/physrevlett.127.247001] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 11/12/2021] [Indexed: 06/14/2023]
Abstract
We show that in a two-dimensional electron gas with an annular Fermi surface, long-range Coulomb interactions can lead to unconventional superconductivity by the Kohn-Luttinger mechanism. Superconductivity is strongly enhanced when the inner and outer Fermi surfaces are close to each other. The most prevalent state has chiral p-wave symmetry, but d-wave and extended s-wave pairing are also possible. We discuss these results in the context of rhombohedral trilayer graphene, where superconductivity was recently discovered in regimes where the normal state has an annular Fermi surface. Using realistic parameters, our mechanism can account for the order of magnitude of T_{c}, as well as its trends as a function of electron density and perpendicular displacement field. Moreover, it naturally explains some of the outstanding puzzles in this material, that include the weak temperature dependence of the resistivity above T_{c}, and the proximity of spin singlet superconductivity to the ferromagnetic phase.
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Affiliation(s)
| | - Tobias Holder
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Maksym Serbyn
- IST Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Erez Berg
- Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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9
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Joucken F, Bena C, Ge Z, Quezada-Lopez E, Pinon S, Kaladzhyan V, Taniguchi T, Watanabe K, Ferreira A, Velasco J. Direct Visualization of Native Defects in Graphite and Their Effect on the Electronic Properties of Bernal-Stacked Bilayer Graphene. NANO LETTERS 2021; 21:7100-7108. [PMID: 34415771 DOI: 10.1021/acs.nanolett.1c01442] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Graphite crystals used to prepare graphene-based heterostructures are generally assumed to be defect free. We report here scanning tunneling microscopy results that show graphite commonly used to prepare graphene devices can contain a significant amount of native defects. Extensive scanning of the surface allows us to determine the concentration of native defects to be 6.6 × 108 cm-2. We further study the effects of these native defects on the electronic properties of Bernal-stacked bilayer graphene. We observe gate-dependent intravalley scattering and successfully compare our experimental results to T-matrix-based calculations, revealing a clear carrier density dependence in the distribution of the scattering vectors. We also present a technique for evaluating the spatial distribution of short-scale scattering. Finally, we present a theoretical analysis based on the Boltzmann transport equation that predicts that the dilute native defects identified in our study are an important extrinsic source of scattering, ultimately setting the charge carrier mobility at low temperatures.
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Affiliation(s)
- Frédéric Joucken
- Department of Physics, University of California, Santa Cruz, California 95064, United States
- Department of Physics, Arizona State University, Tempe, Arizona 85287, United States
| | - Cristina Bena
- Institut de Physique Théorique, Université Paris Saclay, CEA CNRS, Orme des Merisiers, 91190 Gif-sur-Yvette Cedex, France
| | - Zhehao Ge
- Department of Physics, University of California, Santa Cruz, California 95064, United States
| | - Eberth Quezada-Lopez
- Department of Physics, University of California, Santa Cruz, California 95064, United States
| | - Sarah Pinon
- Institut de Physique Théorique, Université Paris Saclay, CEA CNRS, Orme des Merisiers, 91190 Gif-sur-Yvette Cedex, France
| | - Vardan Kaladzhyan
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Aires Ferreira
- Department of Physics and York Centre for Quantum Technologies, University of York, York YO10 5DD, United Kingdom
| | - Jairo Velasco
- Department of Physics, University of California, Santa Cruz, California 95064, United States
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10
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Hirata M, Kobayashi A, Berthier C, Kanoda K. Interacting chiral electrons at the 2D Dirac points: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2021; 84:036502. [PMID: 33059346 DOI: 10.1088/1361-6633/abc17c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 10/15/2020] [Indexed: 06/11/2023]
Abstract
The pseudo-relativistic chiral electrons in 2D graphene and 3D topological semimetals, known as the massless Dirac or Weyl fermions, constitute various intriguing issues in modern condensed-matter physics. In particular, the issues linked to the Coulomb interaction between the chiral electrons attract great attentions due to their unusual features, namely, the interaction is not screened and has a long-ranged property near the charge-neutrality point, in clear contrast to its screened and short-ranged properties in the conventional correlated materials. In graphene, this long-range interaction induces an anomalous logarithmic renormalization of the Fermi velocity, which causes a nonlinear reshaping of its Dirac cone. In addition, for strong interactions, it even leads to the predictions of an excitonic condensation with a spontaneous mass generation. The interaction, however, would seem to be not that large in graphene, so that the latter phenomenon appears to have not yet been observed. Contrastingly, the interaction is probably large in the pressurized organic materialα-(BEDT-TTF)2I3, where a 2D massless-Dirac-fermion phase emerges next to a correlated insulating phase. Therefore, an excellent testing ground would appear in this material for the studies of both the velocity renormalization and the mass generation, as well as for those of the short-range electronic correlations. In this review, we give an overview of the recent progress on the understanding of such interacting chiral electrons in 2D, by placing particular emphasis on the studies in graphene andα-(BEDT-TTF)2I3. In the first half, we briefly summarize our current experimental and theoretical knowledge about the interaction effects in graphene, then turn attentions to the understanding inα-(BEDT-TTF)2I3, and highlight its relevance to and difference from graphene. The second half of this review focusses on the studies linked to the nuclear magnetic resonance experiments and the associated model calculations inα-(BEDT-TTF)2I3. These studies allow us to discuss the anisotropic reshaping of a tilted Dirac cone together with various electronic correlations, and the precursor excitonic dynamics growing prior to a condensation. We see these provide unique opportunities to resolve the momentum dependence of the spin excitations and fluctuations that are strongly influenced by the long-range interaction near the Dirac points.
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Affiliation(s)
- Michihiro Hirata
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan
- MPA-Q, Los Alamos National Laboratory, NM 87545, United States of America
| | - Akito Kobayashi
- Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Claude Berthier
- Laboratoire National des Champs Magnétiques Intenses, UPR 3228 CNRS, EMFL, UGA, UPS and INSA, Boite Postale 166, 38042 Grenoble Cedex 9, France
| | - Kazushi Kanoda
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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11
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Abstract
Graphene is a good candidate for protective material owing to its extremely high stiffness and high strength-to-weight ratio. However, the impact performance of twisted bilayer graphene is still obscure. Herein we have investigated the ballistic resistance capacity of twisted bilayer graphene compared to that of AA-stacked bilayer graphene using molecular dynamic simulations. The energy propagation processes are identical, while the ballistic resistance capacity of the twisted bilayer graphene is almost two times larger than the AA-bilayer graphene. The enhanced capacity of the twisted bilayer graphene is assumed to be caused by the mismatch between the two sheets of graphene, which results in earlier fracture of the first graphene layer and reduces the possibility of penetration.
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12
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Jayaraman A, Hsieh K, Ghawri B, Mahapatra PS, Watanabe K, Taniguchi T, Ghosh A. Evidence of Lifshitz Transition in the Thermoelectric Power of Ultrahigh-Mobility Bilayer Graphene. NANO LETTERS 2021; 21:1221-1227. [PMID: 33502864 DOI: 10.1021/acs.nanolett.0c03586] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Resolving low-energy features in the density of states (DOS) holds the key to understanding a wide variety of rich novel phenomena in graphene-based 2D heterostructures. The Lifshitz transition in bilayer graphene (BLG) arising from trigonal warping has been established theoretically and experimentally. Nevertheless, the experimental realization of its effects on transport properties has been challenging because of its relatively low energy scale (∼1 meV). In this work, we demonstrate that the thermoelectric power (TEP) can be used as an effective probe to investigate fine changes in the DOS of BLG. We observed additional entropy features in the vicinity of the charge neutrality point (CNP) in gapped BLG. This apparent violation of the Mott formula can be explained quantitatively by considering the effects of trigonal warping, thereby serving as possible evidence of a Lifshitz transition.
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Affiliation(s)
- Aditya Jayaraman
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
| | - Kimberly Hsieh
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
| | - Bhaskar Ghawri
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
| | | | - 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
| | - Arindam Ghosh
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
- Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012, India
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13
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Imran M. Quantizing viscous transport in bilayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 33:045603. [PMID: 32947267 DOI: 10.1088/1361-648x/abb9b9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 09/18/2020] [Indexed: 06/11/2023]
Abstract
The momentum transport in ultraclean bilayer graphene is characterized by the viscous transport. In quantizing magnetic field the momentum current passes through the guiding center of the cyclotron orbit. In this study we derive the formula of the quantized Hall viscosity for bilayer graphene. This can be detected in the non-local magnetoresistivity measurements that varies with the quantized step. For weak magnetic field the Landau levels start overlapping and lead to the Shubnikov-de-Haas oscillations, superimposed on the classical formulae, reference Steinberg (1958Phys. Rev.1091486). These oscillations are present in the longitudinal and Hall viscosities.
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Affiliation(s)
- Muhammad Imran
- Department of Physics, University of Florida, Gainesville, Florida 32611, United States of America
- Department of Physics, Leifson Physics, University of Nevada, Reno, Nevada 89512, United States of America
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14
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Li F, Wang L, Li M, Lei L. Hydrophilic encapsulation of reduced graphite oxide (r-GO) by admicellar polymerization for application in biosensors. NEW J CHEM 2019. [DOI: 10.1039/c9nj03793d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Hydrophilic encapsulation of reduced graphite oxide (r-GO) was achieved by admicellar polymerization.
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Affiliation(s)
- Feifei Li
- Key Laboratory of Synthetic and Natural Functional Molecular Chemistry of the Ministry of Education/Shaanxi Provincial Key Laboratory of Electroanalytical Chemistry
- College of Chemistry and Materials Science
- Northwest University
- Xi'an
- P. R. China
| | - Luyao Wang
- Key Laboratory of Synthetic and Natural Functional Molecular Chemistry of the Ministry of Education/Shaanxi Provincial Key Laboratory of Electroanalytical Chemistry
- College of Chemistry and Materials Science
- Northwest University
- Xi'an
- P. R. China
| | - Mengmeng Li
- Key Laboratory of Synthetic and Natural Functional Molecular Chemistry of the Ministry of Education/Shaanxi Provincial Key Laboratory of Electroanalytical Chemistry
- College of Chemistry and Materials Science
- Northwest University
- Xi'an
- P. R. China
| | - Lin Lei
- Key Laboratory of Synthetic and Natural Functional Molecular Chemistry of the Ministry of Education/Shaanxi Provincial Key Laboratory of Electroanalytical Chemistry
- College of Chemistry and Materials Science
- Northwest University
- Xi'an
- P. R. China
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15
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Nam Y, Ki DK, Soler-Delgado D, Morpurgo AF. A family of finite-temperature electronic phase transitions in graphene multilayers. Science 2018; 362:324-328. [PMID: 30337406 DOI: 10.1126/science.aar6855] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 08/28/2018] [Indexed: 12/24/2022]
Abstract
Suspended Bernal-stacked graphene multilayers up to an unexpectedly large thickness exhibit a broken-symmetry ground state whose origin remains to be understood. We show that a finite-temperature second-order phase transition occurs in multilayers whose critical temperature (T c) increases from 12 kelvins (K) in bilayers to 100 K in heptalayers. A comparison of the data with a phenomenological model inspired by a mean-field approach suggests that the transition is associated with the appearance of a self-consistent valley- and spin-dependent staggered potential that changes sign from one layer to the next, appearing at T c and increasing upon cooling. The systematic evolution with thickness of several measured quantities imposes constraints on any microscopic theory aiming to analyze the nature of electronic correlations in this system.
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Affiliation(s)
- Youngwoo Nam
- Department of Quantum Matter Physics (DQMP) and Group of Applied Physics (GAP), University of Geneva, 24 Quai Ernest-Ansermet, CH1211 Genéve 4, Switzerland.,Department of Physics, Gyeongsang National University, Jinju-daero 501, Jinju-si, South Korea
| | - Dong-Keun Ki
- Department of Quantum Matter Physics (DQMP) and Group of Applied Physics (GAP), University of Geneva, 24 Quai Ernest-Ansermet, CH1211 Genéve 4, Switzerland.,Department of Physics, The University of Hong Kong, Hong Kong, China
| | - David Soler-Delgado
- Department of Quantum Matter Physics (DQMP) and Group of Applied Physics (GAP), University of Geneva, 24 Quai Ernest-Ansermet, CH1211 Genéve 4, Switzerland
| | - Alberto F Morpurgo
- Department of Quantum Matter Physics (DQMP) and Group of Applied Physics (GAP), University of Geneva, 24 Quai Ernest-Ansermet, CH1211 Genéve 4, Switzerland.
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16
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Selvi H, Hill EW, Parkinson P, Echtermeyer TJ. Graphene-silicon-on-insulator (GSOI) Schottky diode photodetectors. NANOSCALE 2018; 10:18926-18935. [PMID: 30298152 DOI: 10.1039/c8nr05285a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Graphene-silicon (GS) Schottky junctions have been demonstrated as an efficient architecture for photodetection. However, the response speed of such devices for free space light detection has so far been limited to 10s-100s of kHz for wavelength λ >500 nm. Here, we demonstrate GS Schottky junction photodetectors fabricated on a silicon-on-insulator substrate (SOI) with response speeds approaching 1 GHz, attributed to the reduction of the photo-active silicon layer thickness to 10 μm and with it a suppression of speed-limiting diffusion currents. Graphene-silicon-on-insulator photodetectors (GSOI-PDs) exhibit a negligible influence of wavelength on response speed and only a modest compromise in responsivities compared to GS junctions fabricated on bulk silicon. Noise-equivalent-power (NEP) and specific detectivity (D*) of GSOI photodetectors are 14.5 pW and 7.83 × 1010 cm Hz1/2 W-1, respectively, in ambient conditions. We further demonstrate that combining GSOI-PDs with micro-optical elements formed by modifying the surface topography enables engineering of the spectral and angular response.
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Affiliation(s)
- Hakan Selvi
- School of Electrical & Electronic Engineering, University of Manchester, Manchester M13 9PL, UK.
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17
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Rudenko AN, Stepanov EA, Lichtenstein AI, Katsnelson MI. Excitonic Instability and Pseudogap Formation in Nodal Line Semimetal ZrSiS. PHYSICAL REVIEW LETTERS 2018; 120:216401. [PMID: 29883184 DOI: 10.1103/physrevlett.120.216401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Revised: 03/26/2018] [Indexed: 06/08/2023]
Abstract
Electron correlation effects are studied in ZrSiS using a combination of first-principles and model approaches. We show that basic electronic properties of ZrSiS can be described within a two-dimensional lattice model of two nested square lattices. A high degree of electron-hole symmetry characteristic for ZrSiS is one of the key features of this model. Having determined model parameters from first-principles calculations, we then explicitly take electron-electron interactions into account and show that, at moderately low temperatures, ZrSiS exhibits excitonic instability, leading to the formation of a pseudogap in the electronic spectrum. The results can be understood in terms of Coulomb-interaction-assisted pairing of electrons and holes reminiscent of that of an excitonic insulator. Our finding allows us to provide a physical interpretation of the unusual mass enhancement of charge carriers in ZrSiS recently observed experimentally.
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Affiliation(s)
- A N Rudenko
- School of Physics and Technology, Wuhan University, Wuhan 430072, China
- Institute for Molecules and Materials, Radboud University, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - E A Stepanov
- Institute for Molecules and Materials, Radboud University, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - A I Lichtenstein
- Institute for Theoretical Physics, University of Hamburg, Jungiusstrasse 9, D-20355 Hamburg, Germany
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
| | - M I Katsnelson
- Institute for Molecules and Materials, Radboud University, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
- Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19, 620002 Ekaterinburg, Russia
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18
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Shi Y, Che S, Zhou K, Ge S, Pi Z, Espiritu T, Taniguchi T, Watanabe K, Barlas Y, Lake R, Lau CN. Tunable Lifshitz Transitions and Multiband Transport in Tetralayer Graphene. PHYSICAL REVIEW LETTERS 2018; 120:096802. [PMID: 29547315 DOI: 10.1103/physrevlett.120.096802] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Indexed: 06/08/2023]
Abstract
As the Fermi level and band structure of two-dimensional materials are readily tunable, they constitute an ideal platform for exploring the Lifshitz transition, a change in the topology of a material's Fermi surface. Using tetralayer graphene that host two intersecting massive Dirac bands, we demonstrate multiple Lifshitz transitions and multiband transport, which manifest as a nonmonotonic dependence of conductivity on the charge density n and out-of-plane electric field D, anomalous quantum Hall sequences and Landau level crossings that evolve with n, D, and B.
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Affiliation(s)
- Yanmeng Shi
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
| | - Shi Che
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
| | - Kuan Zhou
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
| | - Supeng Ge
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
| | - Ziqi Pi
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
| | - Timothy Espiritu
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Yafis Barlas
- Department of Electrical and Computer Engineering, University of California, Riverside, Riverside, California 92521, USA
| | - Roger Lake
- Department of Electrical and Computer Engineering, University of California, Riverside, Riverside, California 92521, USA
| | - Chun Ning Lau
- Department of Physics and Astronomy, University of California, Riverside, Riverside, California 92521, USA
- Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
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19
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Li J, Tupikov Y, Watanabe K, Taniguchi T, Zhu J. Effective Landau Level Diagram of Bilayer Graphene. PHYSICAL REVIEW LETTERS 2018; 120:047701. [PMID: 29437431 DOI: 10.1103/physrevlett.120.047701] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 11/18/2017] [Indexed: 06/08/2023]
Abstract
The E=0 octet of bilayer graphene in the filling factor range of -4<ν<4 is a fertile playground for many-body phenomena, yet a Landau level diagram is missing due to strong interactions and competing quantum degrees of freedom. We combine measurements and modeling to construct an empirical and quantitative spectrum. The single-particlelike diagram incorporates interaction effects effectively and provides a unified framework to understand the occupation sequence, gap energies, and phase transitions observed in the octet. It serves as a new starting point for more sophisticated calculations and experiments.
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Affiliation(s)
- Jing Li
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Yevhen Tupikov
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Jun Zhu
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
- Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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20
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Gonzalez-Arraga LA, Lado JL, Guinea F, San-Jose P. Electrically Controllable Magnetism in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2017; 119:107201. [PMID: 28949176 DOI: 10.1103/physrevlett.119.107201] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Indexed: 06/07/2023]
Abstract
Twisted graphene bilayers develop highly localized states around AA-stacked regions for small twist angles. We show that interaction effects may induce either an antiferromagnetic or a ferromagnetic (FM) polarization of said regions, depending on the electrical bias between layers. Remarkably, FM-polarized AA regions under bias develop spiral magnetic ordering, with a relative 120° misalignment between neighboring regions due to a frustrated antiferromagnetic exchange. This remarkable spiral magnetism emerges naturally without the need of spin-orbit coupling, and competes with the more conventional lattice-antiferromagnetic instability, which interestingly develops at smaller bias under weaker interactions than in monolayer graphene, due to Fermi velocity suppression. This rich and electrically controllable magnetism could turn twisted bilayer graphene into an ideal system to study frustrated magnetism in two dimensions.
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Affiliation(s)
| | - J L Lado
- QuantaLab, International Iberian Nanotechnology Laboratory (INL), Avenida Mestre Jose Veiga, 4715-330 Braga, Portugal
| | - Francisco Guinea
- IMDEA Nanociencia, Calle de Faraday, 9, Cantoblanco, 28049 Madrid, Spain
- School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Pablo San-Jose
- Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Cantoblanco, 28049 Madrid, Spain
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21
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Shallcross S, Sharma S, Weber HB. Anomalous Dirac point transport due to extended defects in bilayer graphene. Nat Commun 2017; 8:342. [PMID: 28839136 PMCID: PMC5571127 DOI: 10.1038/s41467-017-00397-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2016] [Accepted: 06/27/2017] [Indexed: 11/21/2022] Open
Abstract
Charge transport at the Dirac point in bilayer graphene exhibits two dramatically different transport states, insulating and metallic, that occur in apparently otherwise indistinguishable experimental samples. We demonstrate that the existence of these two transport states has its origin in an interplay between evanescent modes, that dominate charge transport near the Dirac point, and disordered configurations of extended defects in the form of partial dislocations. In a large ensemble of bilayer systems with randomly positioned partial dislocations, the distribution of conductivities is found to be strongly peaked at both the insulating and metallic limits. We argue that this distribution form, that occurs only at the Dirac point, lies at the heart of the observation of both metallic and insulating states in bilayer graphene. In seemingly indistinguishable bilayer graphene samples, two distinct transport regimes, insulating and metallic, have been identified experimentally. Here, the authors demonstrate that these two states originate from the interplay between extended defects and evanescent modes at the Dirac point.
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Affiliation(s)
- Sam Shallcross
- Lehrstuhl für Theoretische Festkörperphysik, Staudstr. 7-B2, 91058, Erlangen, Germany.
| | - Sangeeta Sharma
- Max-Planck-Institut für Mikrostrukturphysik Weinberg 2, D-06120, Halle, Germany
| | - Heiko B Weber
- Lehrstuhl für Angewandte Physik, Staudtstr. 7, 91058, Erlangen, Germany.,Interdisziplinäres Zentrum für Molekulare Materialien, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, 91058, Germany
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22
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Konstantinidis NP. Capped carbon nanotubes with a number of ground state magnetization discontinuities increasing with their size. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:215803. [PMID: 28437255 DOI: 10.1088/1361-648x/aa6bd4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The classical ground state magnetic response of fullerene molecules that resemble capped carbon nanotubes is calculated within the framework of the antiferromagnetic Heisenberg model. It is found that the magnetic response depends subtly on spatial symmetry and chirality. Clusters based on armchair carbon nanotubes which are capped with non-neighboring pentagons and have D 5d spatial symmetry have a number of magnetization discontinuities which increases with their size. This occurs even though the model completely lacks magnetic anisotropy, and even though the only source of frustration are the two groups of six pentagons located at the ends of the molecules, which become more strongly outnumbered as the clusters are filled in the middle with more unfrustrated hexagons with increasing size. For the cluster with 180 vertices there are already seven magnetization and one susceptibility discontinuities. Contrary to that, similar molecules which have D 5h spatial symmetry reach a limit of one magnetization and two susceptibility ground state discontinuities, while fullerene molecules based on zigzag carbon nanotubes and capped by neighboring pentagons also reach a fixed number of discontinuities with increasing size.
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23
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Feldman BE, Randeria MT, Gyenis A, Wu F, Ji H, Cava RJ, MacDonald AH, Yazdani A. Observation of a nematic quantum Hall liquid on the surface of bismuth. Science 2016; 354:316-321. [DOI: 10.1126/science.aag1715] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 09/23/2016] [Indexed: 11/02/2022]
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24
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Goykhman I, Sassi U, Desiatov B, Mazurski N, Milana S, de Fazio D, Eiden A, Khurgin J, Shappir J, Levy U, Ferrari AC. On-Chip Integrated, Silicon-Graphene Plasmonic Schottky Photodetector with High Responsivity and Avalanche Photogain. NANO LETTERS 2016; 16:3005-13. [PMID: 27053042 PMCID: PMC4868376 DOI: 10.1021/acs.nanolett.5b05216] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 04/02/2016] [Indexed: 05/21/2023]
Abstract
We report an on-chip integrated metal graphene-silicon plasmonic Schottky photodetector with 85 mA/W responsivity at 1.55 μm and 7% internal quantum efficiency. This is one order of magnitude higher than metal-silicon Schottky photodetectors operated in the same conditions. At a reverse bias of 3 V, we achieve avalanche multiplication, with 0.37A/W responsivity and avalanche photogain ∼2. This paves the way to graphene integrated silicon photonics.
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Affiliation(s)
- Ilya Goykhman
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 OFA, U.K.
| | - Ugo Sassi
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 OFA, U.K.
| | - Boris Desiatov
- Department of Applied
Physics, The Benin School of Engineering and Computer Science, The Hebrew University, Jerusalem 91904, Israel
| | - Noa Mazurski
- Department of Applied
Physics, The Benin School of Engineering and Computer Science, The Hebrew University, Jerusalem 91904, Israel
| | - Silvia Milana
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 OFA, U.K.
| | - Domenico de Fazio
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 OFA, U.K.
| | - Anna Eiden
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 OFA, U.K.
| | - Jacob Khurgin
- Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Joseph Shappir
- Department of Applied
Physics, The Benin School of Engineering and Computer Science, The Hebrew University, Jerusalem 91904, Israel
| | - Uriel Levy
- Department of Applied
Physics, The Benin School of Engineering and Computer Science, The Hebrew University, Jerusalem 91904, Israel
| | - Andrea C. Ferrari
- Cambridge Graphene Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 OFA, U.K.
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25
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Yan J, Li C, Zhan D, Liu L, Shen D, Kuo JL, Chen S, Shen Z. Graphene homojunction: closed-edge bilayer graphene by pseudospin interaction. NANOSCALE 2016; 8:9102-9106. [PMID: 26809883 DOI: 10.1039/c5nr08083e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Depending on the sublattices they are propagated in, low-energy electrons or holes are labeled with pseudospin. By engineering pseudospin interactions, we propose that two critical features of a junction, i.e., band gap opening and spatial charge separation, can be realized in graphene layers with proper stacking. We also demonstrate theoretically that such a graphene diode may play a role in future pseudospin electronics such as for harvesting solar energy.
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Affiliation(s)
- Jiaxu Yan
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
| | - Chao Li
- College of Physics, Jilin University, Changchun 130012, People's Republic of China
| | - Da Zhan
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
| | - Lei Liu
- Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, People's Republic of China.
| | - Dezhen Shen
- Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, People's Republic of China.
| | - Jer-Lai Kuo
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Shoushun Chen
- School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Zexiang Shen
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
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26
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Da HX, Yan XH. Faraday rotation in bilayer graphene-based integrated microcavity. OPTICS LETTERS 2016; 41:151-154. [PMID: 26696181 DOI: 10.1364/ol.41.000151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Bernal-stacked bilayer graphene has rich ground states with various broken symmetries, allowing the existence of magneto-optical (MO) effects even in the absence of an external magnetic field. Here we report controllable Faraday rotation (FR) of bilayer graphene induced by electrostatic gate voltage, whose value is 10 times smaller than the case of single layer graphene with a magnetic field. A proposed bilayer graphene-based microcavity configuration enables the enhanced FR angle due to the large localized electromagnetic field. Our results offer unique opportunities to apply bilayer graphene for MO devices.
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27
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Lee KW, Lee CE. Extreme sensitivity of the electric-field-induced band gap to the electronic topological transition in sliding bilayer graphene. Sci Rep 2015; 5:17490. [PMID: 26635178 PMCID: PMC4669455 DOI: 10.1038/srep17490] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 10/30/2015] [Indexed: 11/25/2022] Open
Abstract
We have investigated the effect of electronic topological transition on the electric field-induced band gap in sliding bilayer graphene by using the density functional theory calculations. The electric field-induced band gap was found to be extremely sensitive to the electronic topological transition. At the electronic topological transition induced by layer sliding, four Dirac cones in the Bernal-stacked bilayer graphene reduces to two Dirac cones with equal or unequal Dirac energies depending on the sliding direction. While the critical electric field required for the band gap opening increases with increasing lateral shift for the two Dirac cones with unequal Dirac energies, the critical field is essentially zero with or without a lateral shift for the two Dirac cones with equal Dirac energies. The critical field is determined by the Dirac energy difference and the electronic screening effect. The electronic screening effect was also found to be enhanced with increasing lateral shift, apparently indicating that the massless helical and massive chiral fermions are responsible for the perfect and imperfect electronic screening, respectively.
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Affiliation(s)
- Kyu Won Lee
- Department of Physics, Korea University, Seoul 136-713, Korea
| | - Cheol Eui Lee
- Department of Physics, Korea University, Seoul 136-713, Korea
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28
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Wang P, Cheng B, Martynov O, Miao T, Jing L, Taniguchi T, Watanabe K, Aji V, Lau CN, Bockrath M. Topological Winding Number Change and Broken Inversion Symmetry in a Hofstadter's Butterfly. NANO LETTERS 2015; 15:6395-6399. [PMID: 26401645 DOI: 10.1021/acs.nanolett.5b01568] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Graphene's quantum Hall features are associated with a π Berry's phase due to its odd topological pseudospin winding number. In nearly aligned graphene-hexagonal BN heterostructures, the lattice and orientation mismatch produce a superlattice potential, yielding secondary Dirac points in graphene's electronic spectrum, and under a magnetic field, a Hofstadter butterfly-like energy spectrum. Here we report an additional π Berry's phase shift when tuning the Fermi level past the secondary Dirac points, originating from a change in topological winding number from odd to even when the Fermi-surface electron orbit begins to enclose the secondary Dirac points. At large hole doping inversion symmetry breaking generates a distinct hexagonal pattern in the longitudinal resistivity versus magnetic field and charge density. Major Hofstadter butterfly features persist up to ∼100 K, demonstrating the robustness of the fractal energy spectrum in these systems.
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Affiliation(s)
- Peng Wang
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Bin Cheng
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Oleg Martynov
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Tengfei Miao
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Lei Jing
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan
| | - Vivek Aji
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Chun Ning Lau
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Marc Bockrath
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
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29
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Tian YH, Huang J, Sheng X, Sumpter BG, Yoon M, Kertesz M. Nitrogen Doping Enables Covalent-Like π-π Bonding between Graphenes. NANO LETTERS 2015; 15:5482-91. [PMID: 26151153 DOI: 10.1021/acs.nanolett.5b01940] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The neighboring layers in bilayer (and few-layer) graphenes of both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) π-π bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the π-π overlap across the vdW gap while the individual layers maintain their in-plane π-conjugation and are accordingly planar. The existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.
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Affiliation(s)
- Yong-Hui Tian
- †College of Life Sciences, Research Center of Analytical Instrumentation, Sichuan University, Chengdu, Sichuan 610064, P. R. China
| | - Jingsong Huang
- ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Xiaolan Sheng
- †College of Life Sciences, Research Center of Analytical Instrumentation, Sichuan University, Chengdu, Sichuan 610064, P. R. China
| | - Bobby G Sumpter
- ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Mina Yoon
- ‡Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Miklos Kertesz
- §Department of Chemistry, Georgetown University, 37th and O Streets, NW, Washington, D.C. 20057, United States
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30
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Cheng CM, Xie LF, Pachoud A, Moser HO, Chen W, Wee ATS, Castro Neto AH, Tsuei KD, Özyilmaz B. Anomalous spectral features of a neutral bilayer graphene. Sci Rep 2015; 5:10025. [PMID: 25985064 PMCID: PMC4434949 DOI: 10.1038/srep10025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 02/23/2015] [Indexed: 11/11/2022] Open
Abstract
Graphene and its bilayer are two-dimensional systems predicted to show exciting many-body effects near the neutrality point. The ideal tool to investigate spectrum reconstruction effects is angle-resolved photoemission spectroscopy (ARPES) as it probes directly the band structure with information about both energy and momentum. Here we reveal, by studying undoped exfoliated bilayer graphene with ARPES, two essential aspects of its many-body physics: the electron-phonon scattering rate has an anisotropic k-dependence and the type of electronic liquid is non-Fermi liquid. The latter behavior is evident from an observed electron-electron scattering rate that scales linearly with energy from 100 meV to 600 meV and that is associated with the proximity of bilayer graphene to a two-dimensional quantum critical point of competing orders.
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Affiliation(s)
- C-M Cheng
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan
| | - L F Xie
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,NanoCore, 4 Engineering Drive 3, National University of Singapore 117576, Singapore
| | - A Pachoud
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Graduate School for Integrative Sciences and Engineering (NGS), National University of Singapore, 28 Medical Drive, 117456, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - H O Moser
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link 117603, Singapore.,Karlsruhe Institute of Technology (KIT), Network of Excellent Retired Scientists (NES) and Institute of Microstructure Technology (IMT), Postfach 3640, 76021 Karlsruhe, Germany
| | - W Chen
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - A T S Wee
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - A H Castro Neto
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
| | - K-D Tsuei
- National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan.,Department of Physics, National Tsing Hua University, 101 Sec. 2, Kuang-Fu Road, Hsinchu 30013, Taiwan
| | - B Özyilmaz
- Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore.,NanoCore, 4 Engineering Drive 3, National University of Singapore 117576, Singapore.,Centre for Advanced 2D Materials and Graphene Research Centre, Faculty of Science, National University of Singapore, Block S14, Level 6, 6 Science Drive 2, 117546, Singapore
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31
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Ferrari AC, Bonaccorso F, Fal'ko V, Novoselov KS, Roche S, Bøggild P, Borini S, Koppens FHL, Palermo V, Pugno N, Garrido JA, Sordan R, Bianco A, Ballerini L, Prato M, Lidorikis E, Kivioja J, Marinelli C, Ryhänen T, Morpurgo A, Coleman JN, Nicolosi V, Colombo L, Fert A, Garcia-Hernandez M, Bachtold A, Schneider GF, Guinea F, Dekker C, Barbone M, Sun Z, Galiotis C, Grigorenko AN, Konstantatos G, Kis A, Katsnelson M, Vandersypen L, Loiseau A, Morandi V, Neumaier D, Treossi E, Pellegrini V, Polini M, Tredicucci A, Williams GM, Hong BH, Ahn JH, Kim JM, Zirath H, van Wees BJ, van der Zant H, Occhipinti L, Di Matteo A, Kinloch IA, Seyller T, Quesnel E, Feng X, Teo K, Rupesinghe N, Hakonen P, Neil SRT, Tannock Q, Löfwander T, Kinaret J. Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems. NANOSCALE 2015; 7:4598-810. [PMID: 25707682 DOI: 10.1039/c4nr01600a] [Citation(s) in RCA: 982] [Impact Index Per Article: 109.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.
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Affiliation(s)
- Andrea C Ferrari
- Cambridge Graphene Centre, University of Cambridge, Cambridge, CB3 0FA, UK.
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32
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Insulating state in tetralayers reveals an even-odd interaction effect in multilayer graphene. Nat Commun 2015; 6:6419. [PMID: 25732058 PMCID: PMC4366515 DOI: 10.1038/ncomms7419] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Accepted: 01/27/2015] [Indexed: 11/08/2022] Open
Abstract
Close to charge neutrality, the electronic properties of graphene and its multilayers are sensitive to electron-electron interactions. In bilayers, for instance, interactions are predicted to open a gap between valence and conduction bands, turning the system into an insulator. In mono and (Bernal-stacked) trilayers, which remain conducting at low temperature, interactions do not have equally drastic consequences. It is expected that interaction effects become weaker for thicker multilayers, whose behaviour should converge to that of graphite. Here we show that this expectation does not correspond to reality by revealing the occurrence of an insulating state close to charge neutrality in Bernal-stacked tetralayer graphene. The phenomenology-incompatible with the behaviour expected from the single-particle band structure-resembles that observed in bilayers, but the insulating state in tetralayers is visible at higher temperature. We explain our findings, and the systematic even-odd effect of interactions in Bernal-stacked layers of different thickness that emerges from experiments, in terms of a generalization of the interaction-driven, symmetry-broken states proposed for bilayers.
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33
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Rut G, Rycerz A. Magnetoconductance of the Corbino disk in graphene: chiral tunneling and quantum interference in the bilayer case. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:485301. [PMID: 25365979 DOI: 10.1088/0953-8984/26/48/485301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Quantum transport through an impurity-free Corbino disk in bilayer graphene is investigated analytically, using the mode-matching method to give an effective Dirac equation, in the presence of uniform magnetic fields. Similarly as in the monolayer case (see Rycerz 2010 Phys. Rev. B 81 121404; Katsnelson 2010 Europhys. Lett. 89 17001), conductance at the Dirac point shows oscillations with the flux piercing the disk area ΦD characterized by the period Φ(0) = 2 (h/e) ln(R(o)/R(i)), where R(o)(R(i)) is the outer (inner) disk radius. The oscillation magnitude depends either on the radii ratio or on the physical disk size, with the condition for maximal oscillations being R(o)/R(i) ≃ [ Rit⊥/(2ℏvF) ](4/p) (for R(o)/R(i) ≫ 1), where t⊥ is the interlayer hopping integral, vF is the Fermi velocity in graphene, and p is an even integer. Odd-integer values of p correspond to vanishing oscillations for the normal Corbino setup, or to oscillation frequency doubling for the Andreev-Corbino setup. At higher Landau levels, magnetoconductance behaves almost identically in the monolayer and bilayer cases. A brief comparison with the Corbino disk in a two-dimensional electron gas is also provided in order to illustrate the role of chiral tunneling in graphene.
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Affiliation(s)
- Grzegorz Rut
- Marian Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, PL-30059 Kraków, Poland
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34
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Black-Schaffer AM, Honerkamp C. Chiral d-wave superconductivity in doped graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:423201. [PMID: 25238054 DOI: 10.1088/0953-8984/26/42/423201] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A highly unconventional superconducting state with a spin-singlet dx2-y2+/-idxy-wave, or chiral d-wave symmetry has recently been suggested to emerge from electron-electron interactions in doped graphene. It has been argued that graphene doped to the van Hove singularity at 1/4 doping, where the density of states diverge, is particularly likely to be a chiral d-wave superconductor. In this review we summarize the currently mounting theoretical evidence for the existence of a chiral d-wave superconducting state in graphene, obtained with methods ranging from mean-field studies of effective Hamiltonians to angle-resolved renormalization group calculations. We further discuss the multiple distinctive properties of the chiral d-wave superconducting state in graphene, as well as its stability in the presence of disorder. We also review the means of enhancing the chiral d-wave state using proximity-induced superconductivity. The appearance of chiral d-wave superconductivity is intimately linked to the hexagonal crystal lattice and we also offer a brief overview of other materials which have also been proposed to be chiral d-wave superconductors.
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35
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Li Z, Wang J, Liu Z. Intrinsic carrier mobility of Dirac cones: The limitations of deformation potential theory. J Chem Phys 2014; 141:144107. [DOI: 10.1063/1.4897533] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Zhenzhu Li
- College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China and Center for Nanochemistry, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing 100871, China
| | - Jinying Wang
- College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China and Center for Nanochemistry, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing 100871, China
| | - Zhirong Liu
- College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China and Center for Nanochemistry, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing 100871, China
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36
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Li X, Zhang F, Niu Q, MacDonald AH. Spontaneous layer-pseudospin domain walls in bilayer graphene. PHYSICAL REVIEW LETTERS 2014; 113:116803. [PMID: 25259998 DOI: 10.1103/physrevlett.113.116803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Indexed: 06/03/2023]
Abstract
Bilayer graphene is susceptible to a family of unusual broken symmetry states with spin and valley dependent layer polarization. We report on a microscopic study of the domain walls in these systems, demonstrating that they have interesting microscopic structure related to the topological character of the ordered states. We use our results to show that the metal-insulator transition temperature in bilayer graphene is reduced from mean-field estimates by thermal excitation of domain walls.
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Affiliation(s)
- Xiao Li
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Fan Zhang
- Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA
| | - Qian Niu
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA and School of Physics, International Center for Quantum Materials and Collaborative Innovation Center of Quantum Matter, Peking University, Beijing 100871, China
| | - A H MacDonald
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
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37
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Competing ordered states with filling factor two in bilayer graphene. Nat Commun 2014; 5:4550. [DOI: 10.1038/ncomms5550] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2014] [Accepted: 06/27/2014] [Indexed: 11/09/2022] Open
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38
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Vafek O, Murray JM, Cvetkovic V. Superconductivity on the brink of spin-charge order in a doped honeycomb bilayer. PHYSICAL REVIEW LETTERS 2014; 112:147002. [PMID: 24766005 DOI: 10.1103/physrevlett.112.147002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Indexed: 06/03/2023]
Abstract
Using a controlled weak-coupling renormalization group approach, we establish the mechanism of unconventional superconductivity in the vicinity of spin or charge ordered excitonic states for the case of electrons on the Bernal stacked bilayer honeycomb lattice. With one electron per site, this system, physically realized in bilayer graphene, is unstable towards a spontaneous symmetry breaking. Repulsive interactions favor excitonic order, such as a charge nematic and/or a layer antiferromagnet. We find that upon adding charge carriers to the system, the excitonic order is suppressed, and unconventional superconductivity appears in its place, before it is replaced by a Fermi liquid. We focus on firmly establishing this phenomenon using the renormalization group formalism within an idealized model with parabolic touching of conduction and valence bands.
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Affiliation(s)
- Oskar Vafek
- National High Magnetic Field Laboratory and Department of Physics, Florida State University, Tallahasse, Florida 32306, USA
| | - James M Murray
- National High Magnetic Field Laboratory and Department of Physics, Florida State University, Tallahasse, Florida 32306, USA and Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Vladimir Cvetkovic
- National High Magnetic Field Laboratory and Department of Physics, Florida State University, Tallahasse, Florida 32306, USA
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39
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Velasco J, Lee Y, Zhao Z, Jing L, Kratz P, Bockrath M, Lau CN. Transport measurement of Landau level gaps in bilayer graphene with layer polarization control. NANO LETTERS 2014; 14:1324-1328. [PMID: 24484507 DOI: 10.1021/nl4043399] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Landau level (LL) gaps are important parameters for understanding electronic interactions and symmetry-broken processes in bilayer graphene (BLG). Here we present transport spectroscopy measurements of LL gaps in double-gated suspended BLG with high mobilities in the quantum Hall regime. By using bias as a spectroscopic tool, we measure the gap Δ for the quantum Hall (QH) state at filling factors ν = ±4 and -2. The single-particle Δ(ν=4) scales linearly with magnetic field B and is independent of the out-of-plane electric field E⊥. For the symmetry-broken ν = -2 state, the measured values of Δ(ν=-2) are ∼1.1 meV/T and 0.17 meV/T for singly gated geometry and dual-gated geometry at E⊥ = 0, respectively. The difference between the two values arises from the E⊥. dependence of Δ(ν=-2), suggesting that the ν = -2 state is layer polarized. Our studies provide the first measurements of the gaps of the broken symmetry QH states in BLG with well-controlled E⊥ and establish a robust method that can be implemented for studying similar states in other layered materials.
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Affiliation(s)
- J Velasco
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 92521, United States
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40
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San-Jose P, Gorbachev RV, Geim AK, Novoselov KS, Guinea F. Stacking boundaries and transport in bilayer graphene. NANO LETTERS 2014; 14:2052-2057. [PMID: 24605877 DOI: 10.1021/nl500230a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Pristine bilayer graphene behaves in some instances as an insulator with a transport gap of a few millielectronvolts. This behavior has been interpreted as the result of an intrinsic electronic instability induced by many-body correlations. Intriguingly, however, some samples of similar mobility exhibit good metallic properties with a minimal conductivity of the order of 2e(2)/h. Here, we propose an explanation for this dichotomy, which is unrelated to electron interactions and based instead on the reversible formation of boundaries between stacking domains ("solitons"). We argue, using a numerical analysis, that the hallmark features of the previously inferred many-body insulating state can be explained by scattering on boundaries between domains with different stacking order (AB and BA). We furthermore present experimental evidence, reinforcing our interpretation, of reversible switching between a metallic and an insulating regime in suspended bilayers when subjected to thermal cycling or high current annealing.
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Affiliation(s)
- P San-Jose
- Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Cantoblanco, 28049 Madrid, Spain
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41
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Probing Dirac Fermions in Graphene by Scanning Tunneling Microscopy and Spectroscopy. ACTA ACUST UNITED AC 2013. [DOI: 10.1007/978-3-319-02633-6_2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
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42
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Kim KS, Walter AL, Moreschini L, Seyller T, Horn K, Rotenberg E, Bostwick A. Coexisting massive and massless Dirac fermions in symmetry-broken bilayer graphene. NATURE MATERIALS 2013; 12:887-892. [PMID: 23892785 DOI: 10.1038/nmat3717] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 06/20/2013] [Indexed: 06/02/2023]
Abstract
Charge carriers in bilayer graphene are widely believed to be massive Dirac fermions that have a bandgap tunable by a transverse electric field. However, a full transport gap, despite its importance for device applications, has not been clearly observed in gated bilayer graphene, a long-standing puzzle. Moreover, the low-energy electronic structure of bilayer graphene is widely held to be unstable towards symmetry breaking either by structural distortions, such as twist, strain, or electronic interactions that can lead to various ground states. Which effect dominates the physics at low energies is hotly debated. Here we show both by direct band-structure measurements and by calculations that a native imperfection of bilayer graphene, a distribution of twists whose size is as small as ~0.1°, is sufficient to generate a completely new electronic spectrum consisting of massive and massless Dirac fermions. The massless spectrum is robust against strong electric fields, and has a unusual topology in momentum space consisting of closed arcs having an exotic chiral pseudospin texture, which can be tuned by varying the charge density. The discovery of this unusual Dirac spectrum not only complements the framework of massive Dirac fermions, widely relevant to charge transport in bilayer graphene, but also supports the possibility of valley Hall transport.
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Affiliation(s)
- Keun Su Kim
- 1] Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] Department of Molecular Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
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43
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De Padova P, Avila J, Resta A, Razado-Colambo I, Quaresima C, Ottaviani C, Olivieri B, Bruhn T, Vogt P, Asensio MC, Le Lay G. The quasiparticle band dispersion in epitaxial multilayer silicene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:382202. [PMID: 23988580 DOI: 10.1088/0953-8984/25/38/382202] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The growth of multilayer silicene is an exciting challenge for the future of silicon nano-electronics. Here, we use angle-resolved photoemission spectroscopy to map the entire Brillouin zone (BZ) of (√3 × √3)R30° reconstructed epitaxial multilayer silicene islands, growing on top of the first (3 × 3) reconstructed silicene wetting layer, on Ag(111) substrates. We found Λ- and V-shape linear dispersions, which we relate to the π and π* bands of massless quasiparticles in multilayer silicene, at the BZ centre [Formula: see text] and at all the [Formula: see text] centres of the (√3 × √3)R30° Brillouin zones in the extended scheme, due to folding of the Dirac cones at the [Formula: see text] and [Formula: see text] points of the (1 × 1) silicene BZ. The Fermi velocity of ∼0.3 × 10(6) m s(-1) obtained is highly promising for potential silicene-based devices.
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Affiliation(s)
- Paola De Padova
- Consiglio Nazionale delle Ricerche-ISM, via Fosso del Cavaliere 100, I-00133 Roma, Italy.
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44
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Pearce AJ, Cavaliere F, Mariani E. Conductance and shot noise in strained bilayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:375301. [PMID: 23963478 DOI: 10.1088/0953-8984/25/37/375301] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We explore the effect of trigonal warping and of elastic deformations on the electronic spectrum of bilayer graphene devices, on their ballistic conductance as well as on the shot noise. Uniaxial strain distorts the lattice creating a uniform fictitious gauge field in the electronic Dirac Hamiltonian which ultimately causes a dramatic reconstruction in the trigonally warped electronic spectrum, inducing topological transitions in the Fermi surface. In this paper we present results of ballistic transport in bilayer graphene in the absence and presence of strain, with particular focus on noise and the Fano factor F. The inclusion of trigonal warping preserves the pseudo-diffusive value of F = 1/3 at the Dirac point, as calculated in the absence of trigonal warping terms. However, the range of energies which show pseudo-diffusive transport increases by orders of magnitude compared to the results stemming out of a parabolic spectrum and the applied strain acts to increase this energy range further.
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Affiliation(s)
- Alexander J Pearce
- Centre for Graphene Science, School of Physics, University of Exeter, Stocker Road, EX4 4QL Exeter, UK
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45
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Strain and curvature induced evolution of electronic band structures in twisted graphene bilayer. Nat Commun 2013; 4:2159. [DOI: 10.1038/ncomms3159] [Citation(s) in RCA: 138] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 06/17/2013] [Indexed: 12/22/2022] Open
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McCann E, Koshino M. The electronic properties of bilayer graphene. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:056503. [PMID: 23604050 DOI: 10.1088/0034-4885/76/5/056503] [Citation(s) in RCA: 201] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
We review the electronic properties of bilayer graphene, beginning with a description of the tight-binding model of bilayer graphene and the derivation of the effective Hamiltonian describing massive chiral quasiparticles in two parabolic bands at low energies. We take into account five tight-binding parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra- and interlayer asymmetry between atomic sites which induce band gaps in the low-energy spectrum. The Hartree model of screening and band-gap opening due to interlayer asymmetry in the presence of external gates is presented. The tight-binding model is used to describe optical and transport properties including the integer quantum Hall effect, and we also discuss orbital magnetism, phonons and the influence of strain on electronic properties. We conclude with an overview of electronic interaction effects.
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Affiliation(s)
- Edward McCann
- Department of Physics, Lancaster University, Lancaster LA1 4YB, UK
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47
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Mkhitaryan VV, Mishchenko EG. Localized states due to expulsion of resonant impurity levels from the continuum in bilayer graphene. PHYSICAL REVIEW LETTERS 2013; 110:086805. [PMID: 23473187 DOI: 10.1103/physrevlett.110.086805] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Indexed: 06/01/2023]
Abstract
The Anderson impurity problem is considered for a graphene bilayer subject to a gap-opening bias. In-gap localized states are produced even when the impurity level overlaps with the continuum of band electrons. The effect depends strongly on the polarity of the applied bias as long as hybridization with the impurity occurs within a single layer. For an impurity level inside the conduction band a positive bias creates the new localized in-gap state. A negative bias does not produce the same result and leads to a simple broadening of the impurity level. The implications for transport are discussed including a possibility of the gate-controlled Kondo effect.
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Affiliation(s)
- V V Mkhitaryan
- Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112, USA
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48
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Lin CL, Arafune R, Kawahara K, Kanno M, Tsukahara N, Minamitani E, Kim Y, Kawai M, Takagi N. Substrate-induced symmetry breaking in silicene. PHYSICAL REVIEW LETTERS 2013; 110:076801. [PMID: 25166389 DOI: 10.1103/physrevlett.110.076801] [Citation(s) in RCA: 121] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Indexed: 05/15/2023]
Abstract
We demonstrate that silicene, a 2D honeycomb lattice consisting of Si atoms, loses its Dirac fermion characteristics due to substrate-induced symmetry breaking when synthesized on the Ag(111) surface. No Landau level sequences appear in the tunneling spectra under a magnetic field, and density functional theory calculations show that the band structure is drastically modified by the hybridization between the Si and Ag atoms. This is the first direct example demonstrating the lack of Dirac fermions in a single layer honeycomb lattice due to significant symmetry breaking.
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Affiliation(s)
- Chun-Liang Lin
- Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, Kashiwa 5-1-5, Chiba 277-8561, Japan
| | - Ryuichi Arafune
- International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Ibaraki 304-0044, Japan
| | - Kazuaki Kawahara
- Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, Kashiwa 5-1-5, Chiba 277-8561, Japan
| | - Mao Kanno
- Department of Applied Chemistry, The University of Tokyo, Hongo 7-3-1, Tokyo 113-8656, Japan
| | - Noriyuki Tsukahara
- Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, Kashiwa 5-1-5, Chiba 277-8561, Japan
| | | | - Yousoo Kim
- RIKEN, 2-1 Hirosawa, Saitama 351-0198, Japan
| | - Maki Kawai
- Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, Kashiwa 5-1-5, Chiba 277-8561, Japan and Department of Applied Chemistry, The University of Tokyo, Hongo 7-3-1, Tokyo 113-8656, Japan
| | - Noriaki Takagi
- Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, Kashiwa 5-1-5, Chiba 277-8561, Japan and Department of Applied Chemistry, The University of Tokyo, Hongo 7-3-1, Tokyo 113-8656, Japan
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Wu T, Shen H, Sun L, You J, Yue Z. Three step fabrication of graphene at low temperature by remote plasma enhanced chemical vapor deposition. RSC Adv 2013. [DOI: 10.1039/c3ra23388j] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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50
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Rakhmanov AL, Rozhkov AV, Sboychakov AO, Nori F. Instabilities of the AA-stacked graphene bilayer. PHYSICAL REVIEW LETTERS 2012; 109:206801. [PMID: 23215515 DOI: 10.1103/physrevlett.109.206801] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Indexed: 06/01/2023]
Abstract
Tight-binding calculations predict that the AA-stacked bilayer graphene has one electron and one hole conducting band, and that the Fermi surfaces of these bands coincide. We demonstrate that as a result of this degeneracy, the bilayer becomes unstable with respect to a set of spontaneous symmetry violations. Which of the symmetries is broken depends on the microscopic details of the system. For strong on-site Coulomb interaction we find that antiferromagnetism is the most stable order parameter. For an on-site repulsion energy typical for graphene systems, the antiferromagnetic gap can exist up to room temperature.
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Affiliation(s)
- A L Rakhmanov
- Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198, Japan
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