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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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Aamir MA, Karnatak P, Jayaraman A, Sai TP, Ramakrishnan TV, Sensarma R, Ghosh A. Marginally Self-Averaging One-Dimensional Localization in Bilayer Graphene. PHYSICAL REVIEW LETTERS 2018; 121:136806. [PMID: 30312065 DOI: 10.1103/physrevlett.121.136806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Revised: 07/07/2018] [Indexed: 06/08/2023]
Abstract
The combination of a field-tunable band gap, topological edge states, and valleys in the band structure makes insulating bilayer graphene a unique localized system, where the scaling laws of dimensionless conductance g remain largely unexplored. Here we show that the relative fluctuations in lng with the varying chemical potential, in strongly insulating bilayer graphene (BLG), decay nearly logarithmically for a channel length up to L/ξ≈20, where ξ is the localization length. This "marginal" self-averaging, and the corresponding dependence of ⟨lng⟩ on L, suggests that transport in strongly gapped BLG occurs along strictly one-dimensional channels, where ξ≈0.5±0.1 μm was found to be much longer than that expected from the bulk band gap. Our experiment reveals a nontrivial localization mechanism in gapped BLG, governed by transport along robust edge modes.
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Affiliation(s)
- Md Ali Aamir
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - Paritosh Karnatak
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - Aditya Jayaraman
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - T Phanindra Sai
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - T V Ramakrishnan
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - Rajdeep Sensarma
- Department of Theoretical Physics, Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Mumbai 400005, India
| | - Arindam Ghosh
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
- Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560 012, India
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Weber B, Ryu H, Tan YHM, Klimeck G, Simmons MY. Limits to metallic conduction in atomic-scale quasi-one-dimensional silicon wires. PHYSICAL REVIEW LETTERS 2014; 113:246802. [PMID: 25541793 DOI: 10.1103/physrevlett.113.246802] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Indexed: 06/04/2023]
Abstract
The recent observation of ultralow resistivity in highly doped, atomic-scale silicon wires has sparked interest in what limits conduction in these quasi-1D systems. Here we present electron transport measurements of gated Si:P wires of widths 4.6 and 1.5 nm. At 4.6 nm we find an electron mobility, μ(el)≃60 cm²/V s, in excellent agreement with that of macroscopic Hall bars. Metallic conduction persists to millikelvin temperatures where we observe Gaussian conductance fluctuations of order δG∼e²/h. In thinner wires (1.5 nm), metallic conduction breaks down at G≲e²/h, where localization of carriers leads to Coulomb blockade. Metallic behavior is explained by the large carrier densities in Si:P δ-doped systems, allowing the occupation of all six valleys of the silicon conduction band, enhancing the number of 1D channels and hence the localization length.
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Affiliation(s)
- Bent Weber
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Hoon Ryu
- National Institute of Supercomputing and Networking, KISTI, Daejeon 305-806, South Korea
| | - Y-H Matthias Tan
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - Gerhard Klimeck
- Network for Computational Nanotechnology, Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - Michelle Y Simmons
- Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
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Pappert K, Schmidt MJ, Hümpfner S, Rüster C, Schott GM, Brunner K, Gould C, Schmidt G, Molenkamp LW. Magnetization-switched metal-insulator transition in a (Ga,Mn)as tunnel device. PHYSICAL REVIEW LETTERS 2006; 97:186402. [PMID: 17155562 DOI: 10.1103/physrevlett.97.186402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Indexed: 05/12/2023]
Abstract
We observe the occurrence of an Efros-Shklovskii gap in (Ga,Mn)As based tunnel junctions. The occurrence of the gap is controlled by the extent of the hole wave function on the Mn acceptor atoms. Using k.p-type calculations we show that this extent depends crucially on the direction of the magnetization in the (Ga,Mn)As (which has two almost equivalent easy axes). This implies one can reversibly tune the system into the insulating or metallic state by changing the magnetization.
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Affiliation(s)
- K Pappert
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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Fogler MM, Malinin SV, Nattermann T. Coulomb blockade and transport in a chain of one-dimensional quantum dots. PHYSICAL REVIEW LETTERS 2006; 97:096601. [PMID: 17026382 DOI: 10.1103/physrevlett.97.096601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2006] [Indexed: 05/12/2023]
Abstract
A long one-dimensional wire with a finite density of strong random impurities is modeled as a chain of weakly coupled quantum dots. At low temperature T and applied voltage V its resistance is limited by breaks: randomly occurring clusters of quantum dots with a special length distribution pattern that inhibit the transport. Because of the interplay of interaction and disorder effects the resistance can exhibit T and V dependences that can be approximated by power laws. The corresponding two exponents differ greatly from each other and depend not only on the intrinsic electronic parameters but also on the impurity distribution statistics.
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Affiliation(s)
- Michael M Fogler
- Department of Physics, University of California San Diego, La Jolla, 9500 Gilman Drive, California 92093, USA
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Fogler MM, Kelley RS. Non-ohmic variable-range hopping transport in one-dimensional conductors. PHYSICAL REVIEW LETTERS 2005; 95:166604. [PMID: 16241828 DOI: 10.1103/physrevlett.95.166604] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2005] [Indexed: 05/05/2023]
Abstract
We investigate theoretically the effect of a finite electric field on the resistivity of a disordered one-dimensional system in the variable-range hopping regime. We find that at low fields the transport is inhibited by rare fluctuations in the random distribution of localized states that create high-resistance breaks in the hopping network. As the field increases, the breaks become less resistive. In strong fields the breaks are overrun and the electron distribution function is driven far from equilibrium. The logarithm of the resistance initially shows a simple exponential drop with the field, followed by a logarithmic dependence, and finally, by an inverse square-root law.
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Affiliation(s)
- M M Fogler
- Department of Physics, University of California San Diego, La Jolla, 92093, USA
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