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Le HA, Lee IH, Kim YH, Eric Yang SR. Phase diagram and crossover phases of topologically ordered graphene zigzag nanoribbons: role of localization effects. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:265604. [PMID: 38547530 DOI: 10.1088/1361-648x/ad38f9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Accepted: 03/28/2024] [Indexed: 04/06/2024]
Abstract
We computed the phase diagram of zigzag graphene nanoribbons as a function of on-site repulsion, doping, and disorder strength. The topologically ordered phase undergoes topological phase transitions into crossover phases, which are new disordered phases with non-universal topological entanglement entropy that exhibits significant variance. We explored the nature of non-local correlations in both the topologically ordered and crossover phases. In the presence of localization effects, strong on-site repulsion and/or doping weaken non-local correlations between the opposite zigzag edges of the topologically ordered phase. In one of the crossover phases, bothe-/2solitonic fractional charges and spin-charge separation were absent; however, charge-transfer correlations between the zigzag edges were possible. Another crossover phase contains solitonice-/2fractional charges but lacks charge transfer correlations. We also observed properties of non-topological, strongly disordered, and strongly repulsive phases. Each phase on the phase diagram exhibits a different zigzag-edge structure. Additionally, we investigated the tunneling of solitonic fractional charges under an applied voltage between the zigzag edges of undoped topologically ordered zigzag ribbons, and found that it may lead to a zero-bias tunneling anomaly.
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Affiliation(s)
- Hoang-Anh Le
- Department of Physics, Korea University, Seoul 02841, Republic of Korea
| | - In-Hwan Lee
- Department of Physics, Korea University, Seoul 02841, Republic of Korea
| | - Young Heon Kim
- Department of Physics, Korea University, Seoul 02841, Republic of Korea
| | - S-R Eric Yang
- Department of Physics, Korea University, Seoul 02841, Republic of Korea
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Jeong YH, Eric Yang SR, Cha MC. Soliton fractional charge of disordered graphene nanoribbon. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:265601. [PMID: 30921770 DOI: 10.1088/1361-648x/ab146b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We investigate the properties of the gap-edge states of half-filled interacting disordered zigzag graphene nanoribbons, and find that the midgap states can display a quantized fractional charge of 1/2. These gap-edge states can be represented by topological kinks with their site probability distribution divided between the left and right zigzag edges with different chiralities. In addition, there are numerous spin-split gap-edge states, similar to those in a Mott-Anderson insulator.
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Affiliation(s)
- Y H Jeong
- Department of Physics, Korea University, Seoul, Republic of Korea
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Soliton Fractional Charges in Graphene Nanoribbon and Polyacetylene: Similarities and Differences. NANOMATERIALS 2019; 9:nano9060885. [PMID: 31207969 PMCID: PMC6630912 DOI: 10.3390/nano9060885] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Revised: 06/07/2019] [Accepted: 06/13/2019] [Indexed: 11/17/2022]
Abstract
An introductory overview of current research developments regarding solitons and fractional boundary charges in graphene nanoribbons is presented. Graphene nanoribbons and polyacetylene have chiral symmetry and share numerous similar properties, e.g., the bulk-edge correspondence between the Zak phase and the existence of edge states, along with the presence of chiral boundary states, which are important for charge fractionalization. In polyacetylene, a fermion mass potential in the Dirac equation produces an excitation gap, and a twist in this scalar potential produces a zero-energy chiral soliton. Similarly, in a gapful armchair graphene nanoribbon, a distortion in the chiral gauge field can produce soliton states. In polyacetylene, a soliton is bound to a domain wall connecting two different dimerized phases. In graphene nanoribbons, a domain-wall soliton connects two topological zigzag edges with different chiralities. However, such a soliton does not display spin-charge separation. The existence of a soliton in finite-length polyacetylene can induce formation of fractional charges on the opposite ends. In contrast, for gapful graphene nanoribbons, the antiferromagnetic coupling between the opposite zigzag edges induces integer boundary charges. The presence of disorder in graphene nanoribbons partly mitigates antiferromagnetic coupling effect. Hence, the average edge charge of gap states with energies within a small interval is e/2, with significant charge fluctuations. However, midgap states exhibit a well-defined charge fractionalization between the opposite zigzag edges in the weak-disorder regime. Numerous occupied soliton states in a disorder-free and doped zigzag graphene nanoribbon form a solitonic phase.
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Kou X, Guo ST, Fan Y, Pan L, Lang M, Jiang Y, Shao Q, Nie T, Murata K, Tang J, Wang Y, He L, Lee TK, Lee WL, Wang KL. Scale-invariant quantum anomalous Hall effect in magnetic topological insulators beyond the two-dimensional limit. PHYSICAL REVIEW LETTERS 2014; 113:137201. [PMID: 25302915 DOI: 10.1103/physrevlett.113.137201] [Citation(s) in RCA: 175] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Indexed: 05/22/2023]
Abstract
We investigate the quantum anomalous Hall effect (QAHE) and related chiral transport in the millimeter-size (Cr(0.12)Bi(0.26)Sb(0.62))₂Te₃ films. With high sample quality and robust magnetism at low temperatures, the quantized Hall conductance of e²/h is found to persist even when the film thickness is beyond the two-dimensional (2D) hybridization limit. Meanwhile, the Chern insulator-featured chiral edge conduction is manifested by the nonlocal transport measurements. In contrast to the 2D hybridized thin film, an additional weakly field-dependent longitudinal resistance is observed in the ten-quintuple-layer film, suggesting the influence of the film thickness on the dissipative edge channel in the QAHE regime. The extension of the QAHE into the three-dimensional thickness region addresses the universality of this quantum transport phenomenon and motivates the exploration of new QAHE phases with tunable Chern numbers. In addition, the observation of scale-invariant dissipationless chiral propagation on a macroscopic scale makes a major stride towards ideal low-power interconnect applications.
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Affiliation(s)
- Xufeng Kou
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Shih-Ting Guo
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Yabin Fan
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Lei Pan
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Murong Lang
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Ying Jiang
- Center for Electron Microscopy and State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Qiming Shao
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Tianxiao Nie
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Koichi Murata
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Jianshi Tang
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Yong Wang
- Center for Electron Microscopy and State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
| | - Liang He
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
| | - Ting-Kuo Lee
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Wei-Li Lee
- Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
| | - Kang L Wang
- Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
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Connolly MR, Puddy RK, Logoteta D, Marconcini P, Roy M, Griffiths JP, Jones GAC, Maksym PA, Macucci M, Smith CG. Unraveling quantum Hall breakdown in bilayer graphene with scanning gate microscopy. NANO LETTERS 2012; 12:5448-5454. [PMID: 23078572 DOI: 10.1021/nl3015395] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Investigating the structure of quantized plateaus in the Hall conductance of graphene is a powerful way of probing its crystalline and electronic structure and will also help to establish whether graphene can be used as a robust standard of resistance for quantum metrology. We use low-temperature scanning gate microscopy to image the interplateau breakdown of the quantum Hall effect in an exfoliated bilayer graphene flake. Scanning gate images captured during breakdown exhibit intricate patterns where the conductance is strongly affected by the presence of the scanning probe tip. The maximum density and intensity of the tip-induced conductance perturbations occur at half-integer filling factors, midway between consecutive quantum Hall plateau, while the intensity of individual sites shows a strong dependence on tip-voltage. Our results are well-described by a model based on quantum percolation which relates the points of high responsivity to tip-induced scattering in a network of saddle points separating localized states.
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Affiliation(s)
- M R Connolly
- Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, United Kingdom.
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Struck A, Kramer B. Electron correlations and single-particle physics in the integer quantum Hall effect. PHYSICAL REVIEW LETTERS 2006; 97:106801. [PMID: 17025841 DOI: 10.1103/physrevlett.97.106801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Indexed: 05/12/2023]
Abstract
The compressibility of a two-dimensional electron system with spin in a spatially correlated random potential and a quantizing magnetic field is investigated. Electron-electron interaction is treated with the Hartree-Fock method. Numerical results for the influences of interaction and disorder on the compressibility as a function of the particle density and the strength of the magnetic field are presented. Localization-delocalization transitions associated with a highly compressible region in the energy spectrum are found at half-integer filling factors. Coulomb blockade effects are found near integer fillings in the regions of low compressibility. Results are compared with recent experiments.
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Affiliation(s)
- Alexander Struck
- I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany
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Morgenstern M, Klijn J, Meyer C, Wiesendanger R. Real-space observation of drift States in a two-dimensional electron system at high magnetic fields. PHYSICAL REVIEW LETTERS 2003; 90:056804. [PMID: 12633386 DOI: 10.1103/physrevlett.90.056804] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2002] [Indexed: 05/24/2023]
Abstract
The local density of states of the adsorbate-induced two-dimensional electron system is studied in magnetic fields up to B=6 T. Landau quantization is observed and drift states with a width of about the magnetic length are found in agreement with theoretical predictions. At the tails of the Landau levels the states form closed paths indicating localization. These states show the expected energy dependence. A multifractal analysis applied to the data results in a nice parabolic shape of the characteristic f(alpha) spectra, but we find only a slight displacement of the origin from alpha=2.0 for the states in the center of the Landau level.
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Affiliation(s)
- M Morgenstern
- Institute of Applied Physics, Hamburg University, Jungiusstrasse 11, Germany
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Zhu JX, Sheng DN, Ting CS. Quasiparticle localization in disordered d-wave superconductors. PHYSICAL REVIEW LETTERS 2000; 85:4944-4947. [PMID: 11102157 DOI: 10.1103/physrevlett.85.4944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2000] [Indexed: 05/23/2023]
Abstract
An extensive numerical study is reported on the disorder effect in two-dimensional d-wave superconductors with random impurities in the unitary limit. It is found that a sharp resonant peak shows up in the density of states at zero energy and correspondingly the finite-size spin conductance is strongly enhanced which results in a nonuniversal feature in one-parameter scaling. However, all quasiparticle states remain localized, indicating that the resonant density peak alone is not sufficient to induce delocalization. In the weak disorder limit, the localization length is so long that the spin conductance at small sample size is close to the universal value predicted by Lee [Phys. Rev. Lett. 71, 1887 (1993)].
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Affiliation(s)
- JX Zhu
- Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, Texas 77204, USA
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Yakubo K, Goto Y. Localization of two-dimensional electrons in a random magnetic field. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 54:13432-13435. [PMID: 9985240 DOI: 10.1103/physrevb.54.13432] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Polyakov DG. Spin-flip scattering in the quantum Hall regime. PHYSICAL REVIEW. B, CONDENSED MATTER 1996; 53:15777-15788. [PMID: 9983414 DOI: 10.1103/physrevb.53.15777] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Lee DH, Wang Z. Effects of electron-electron interactions on the integer quantum Hall transitions. PHYSICAL REVIEW LETTERS 1996; 76:4014-4017. [PMID: 10061170 DOI: 10.1103/physrevlett.76.4014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Berkovits R, Avishai Y. Interacting electrons in disordered potentials: Conductance versus persistent currents. PHYSICAL REVIEW LETTERS 1996; 76:291-294. [PMID: 10061064 DOI: 10.1103/physrevlett.76.291] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Herbut IF, Tesanovic Z. Anomalous diffusion in a high magnetic field and the quasiparticle density of states. PHYSICAL REVIEW. B, CONDENSED MATTER 1995; 52:5160-5163. [PMID: 9981700 DOI: 10.1103/physrevb.52.5160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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