1
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Yuan Y, Liu L, Zhu J, Dong J, Chu Y, Wu F, Du L, Watanabe K, Taniguchi T, Shi D, Zhang G, Yang W. Interplay of Landau Quantization and Interminivalley Scatterings in a Weakly Coupled Moiré Superlattice. NANO LETTERS 2024; 24:6722-6729. [PMID: 38717299 PMCID: PMC11157648 DOI: 10.1021/acs.nanolett.4c01411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2024] [Revised: 05/02/2024] [Accepted: 05/02/2024] [Indexed: 06/06/2024]
Abstract
Double-layer quantum systems are promising platforms for realizing novel quantum phases. Here, we report a study of quantum oscillations (QOs) in a weakly coupled double-layer system composed of a large-angle twisted-double-bilayer graphene (TDBG). We quantify the interlayer coupling strength by measuring the interlayer capacitance from the QOs pattern at low temperatures, revealing electron-hole asymmetry. At high temperatures when SdHOs are thermally smeared, we observe resistance peaks when Landau levels (LLs) from two moiré minivalleys are aligned, regardless of carrier density; eventually, it results in a 2-fold increase of oscillating frequency in D, serving as compelling evidence of the magneto-intersub-band oscillations (MISOs) in double-layer systems. The temperature dependence of MISOs suggests that electron-electron interactions play a crucial role and the scattering times obtained from MISO thermal damping are correlated with the interlayer coupling strength. Our study reveals intriguing interplays among Landau quantization, moiré band structure, and scatterings.
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Affiliation(s)
- Yalong Yuan
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Le Liu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Jundong Zhu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Jingwei Dong
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Yanbang Chu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Fanfan Wu
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Luojun Du
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
| | - Kenji Watanabe
- Research
Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- Research
Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Dongxia Shi
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
- Songshan
Lake Materials Laboratory, Dongguan 523808, People’s
Republic of China
| | - Guangyu Zhang
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
- Songshan
Lake Materials Laboratory, Dongguan 523808, People’s
Republic of China
| | - Wei Yang
- Beijing
National Laboratory for Condensed Matter Physics and Institute of
Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
- School
of Physical Sciences, University of Chinese
Academy of Sciences, Beijing 100190, People’s
Republic of China
- Songshan
Lake Materials Laboratory, Dongguan 523808, People’s
Republic of China
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2
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Hoke JC, Li Y, May-Mann J, Watanabe K, Taniguchi T, Bradlyn B, Hughes TL, Feldman BE. Uncovering the spin ordering in magic-angle graphene via edge state equilibration. Nat Commun 2024; 15:4321. [PMID: 38773076 PMCID: PMC11109299 DOI: 10.1038/s41467-024-48385-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Accepted: 04/30/2024] [Indexed: 05/23/2024] Open
Abstract
The flat bands in magic-angle twisted bilayer graphene (MATBG) provide an especially rich arena to investigate interaction-driven ground states. While progress has been made in identifying the correlated insulators and their excitations at commensurate moiré filling factors, the spin-valley polarizations of the topological states that emerge at high magnetic field remain unknown. Here we introduce a technique based on twist-decoupled van der Waals layers that enables measurement of their electronic band structure and-by studying the backscattering between counter-propagating edge states-the determination of the relative spin polarization of their edge modes. We find that the symmetry-broken quantum Hall states that extend from the charge neutrality point in MATBG are spin unpolarized at even integer filling factors. The measurements also indicate that the correlated Chern insulator emerging from half filling of the flat valence band is spin unpolarized and suggest that its conduction band counterpart may be spin polarized.
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Affiliation(s)
- Jesse C Hoke
- Department of Physics, Stanford University, Stanford, CA, 94305, USA
- Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Yifan Li
- Department of Physics, Stanford University, Stanford, CA, 94305, USA
- Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA
| | - Julian May-Mann
- Department of Physics, Stanford University, Stanford, CA, 94305, USA
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Kenji Watanabe
- Research Center for Electronic and Optical Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Barry Bradlyn
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Taylor L Hughes
- Department of Physics and Institute for Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Benjamin E Feldman
- Department of Physics, Stanford University, Stanford, CA, 94305, USA.
- Geballe Laboratory for Advanced Materials, Stanford, CA, 94305, USA.
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
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3
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Bigeard G, Cresti A. Magic-angle twisted bilayer graphene under orthogonal and in-plane magnetic fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:325502. [PMID: 38670079 DOI: 10.1088/1361-648x/ad4431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2024] [Accepted: 04/26/2024] [Indexed: 04/28/2024]
Abstract
We investigate the effect of a magnetic field on the band structure of bilayer graphene with a magic twist angle of 1.08∘. The coupling of a tight-binding model and the Peierls phase allows the calculation of the energy bands of periodic two-dimensional systems. For an orthogonal magnetic field, the Landau levels are dispersive, particularly for magnetic lengths comparable to or larger than the twisted bilayer cell size. A high in-plane magnetic field modifies the low-energy bands and gap, which we demonstrate to be a direct consequence of the minimal coupling.
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Affiliation(s)
- Gaëlle Bigeard
- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, CROMA, 38000 Grenoble, France
| | - Alessandro Cresti
- Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, CROMA, 38000 Grenoble, France
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4
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Pushkarna I, Pásztor Á, Renner C. Twist-Angle-Dependent Electronic Properties of Exfoliated Single Layer MoS 2 on Au(111). NANO LETTERS 2023; 23:9406-9412. [PMID: 37844067 PMCID: PMC10603799 DOI: 10.1021/acs.nanolett.3c02804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 09/29/2023] [Indexed: 10/18/2023]
Abstract
Synthetic materials and heterostructures obtained by the controlled stacking of exfoliated monolayers are emerging as attractive functional materials owing to their highly tunable properties. We present a detailed scanning tunneling microscopy and spectroscopy study of single layer MoS2-on-gold heterostructures as a function of the twist angle. We find that their electronic properties are determined by the hybridization of the constituent layers and are modulated at the moiré period. The hybridization depends on the layer alignment, and the modulation amplitude vanishes with increasing twist angle. We explain our observations in terms of a hybridization between the nearest sulfur and gold atoms, which becomes spatially more homogeneous and weaker as the moiré periodicity decreases with increasing twist angle, unveiling the possibility of tunable hybridization of electronic states via twist angle engineering.
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Affiliation(s)
| | | | - Christoph Renner
- Department of Quantum Matter
Physics, Université de Genève, 24 Quai Ernest Ansermet, CH-1211 Geneva, Switzerland
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5
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Do TN, Shih PH, Gumbs G. Magnetoplasmons in magic-angle twisted bilayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:455703. [PMID: 37531966 DOI: 10.1088/1361-648x/acecf1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Accepted: 08/02/2023] [Indexed: 08/04/2023]
Abstract
The magic-angle twisted bilayer graphene (MATBLG) has been demonstrated to exhibit exotic physical properties due to the special flat bands. However, exploiting the engineering of such properties by external fields is still in it infancy. Here we show that MATBLG under an external magnetic field presents a distinctive magnetoplasmon dispersion, which can be significantly modified by transferred momentum and charge doping. Along a wide range of transferred momentum, there exist special pronounced single magnetoplasmon and horizontal single-particle excitation modes near charge neutrality. We provide an insightful discussion of such unique features based on the electronic excitation of Landau levels quantized from the flat bands and Landau damping. Additionally, charge doping leads to peculiar multiple strong-weight magnetoplasmons. These characteristics make MATBLG a favorable candidate for plasmonic devices and technology applications.
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Affiliation(s)
- Thi-Nga Do
- Department of Physics, National Cheng Kung University, Tainan 701, Taiwan
| | - Po-Hsin Shih
- Department of Physics and Astronomy, Hunter College of the City University of New York, 695 Park Avenue, New York, NY 10065, United States of America
| | - Godfrey Gumbs
- Department of Physics and Astronomy, Hunter College of the City University of New York, 695 Park Avenue, New York, NY 10065, United States of America
- Donostia International Physics Center (DIPC), P de Manuel Lardizabal, 4, 20018 San Sebastian, Basque Country, Spain
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6
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Liu L, Chu Y, Yang G, Yuan Y, Wu F, Ji Y, Tian J, Yang R, Watanabe K, Taniguchi T, Long G, Shi D, Liu J, Shen J, Lu L, Yang W, Zhang G. Quantum oscillations in field-induced correlated insulators of a moiré superlattice. Sci Bull (Beijing) 2023; 68:1127-1133. [PMID: 37210331 DOI: 10.1016/j.scib.2023.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Revised: 04/03/2023] [Accepted: 04/26/2023] [Indexed: 05/22/2023]
Abstract
We report an observation of quantum oscillations (QOs) in the correlated insulators with valley anisotropy of twisted double bilayer graphene (TDBG). The anomalous QOs are best captured in the magneto resistivity oscillations of the insulators at v = -2, with a period of 1/B and an oscillation amplitude as high as 150 kΩ. The QOs can survive up to ∼10 K, and above 12 K, the insulating behaviors are dominant. The QOs of the insulator are strongly D dependent: the carrier density extracted from the 1/B periodicity decreases almost linearly with D from -0.7 to -1.1 V/nm, suggesting a reduced Fermi surface; the effective mass from Lifshitz-Kosevich analysis depends nonlinearly on D, reaching a minimal value of 0.1 me at D = ∼ -1.0 V/nm. Similar observations of QOs are also found at v = 2, as well as in other devices without graphite gate. We interpret the D sensitive QOs of the correlated insulators in the picture of band inversion. By reconstructing an inverted band model with the measured effective mass and Fermi surface, the density of state at the gap, calculated from thermal broadened Landau levels, agrees qualitatively with the observed QOs in the insulators. While more theoretical understandings are needed in the future to fully account for the anomalous QOs in this moiré system, our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.
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Affiliation(s)
- Le Liu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Yanbang Chu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Guang Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Yalong Yuan
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Fanfan Wu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Yiru Ji
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Jinpeng Tian
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
| | - Rong Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Gen Long
- Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Dongxia Shi
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Jianpeng Liu
- School of Physical Sciences and Technology, ShanghaiTech University, Shanghai 200031, China; ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai 200031, China
| | - Jie Shen
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Li Lu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Wei Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China.
| | - Guangyu Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China; Songshan Lake Materials Laboratory, Dongguan 523808, China.
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7
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Perpendicular electric field drives Chern transitions and layer polarization changes in Hofstadter bands. Nat Commun 2022; 13:7781. [PMID: 36526625 PMCID: PMC9758152 DOI: 10.1038/s41467-022-35421-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 12/02/2022] [Indexed: 12/23/2022] Open
Abstract
Moiré superlattices engineer band properties and enable observation of fractal energy spectra of Hofstadter butterfly. Recently, correlated-electron physics hosted by flat bands in small-angle moiré systems has been at the foreground. However, the implications of moiré band topology within the single-particle framework are little explored experimentally. An outstanding problem is understanding the effect of band topology on Hofstadter physics, which does not require electron correlations. Our work experimentally studies Chern state switching in the Hofstadter regime using twisted double bilayer graphene (TDBG), which offers electric field tunable topological bands, unlike twisted bilayer graphene. Here we show that the nontrivial topology reflects in the Hofstadter spectra, in particular, by displaying a cascade of Hofstadter gaps that switch their Chern numbers sequentially while varying the perpendicular electric field. Our experiments together with theoretical calculations suggest a crucial role of charge polarization changing concomitantly with topological transitions in this system. Layer polarization is likely to play an important role in the topological states in few-layer twisted systems. Moreover, our work establishes TDBG as a novel Hofstadter platform with nontrivial magnetoelectric coupling.
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8
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Wang Y, Gao X, Yang K, Gu P, Lu X, Zhang S, Gao Y, Ren N, Dong B, Jiang Y, Watanabe K, Taniguchi T, Kang J, Lou W, Mao J, Liu J, Ye Y, Han Z, Chang K, Zhang J, Zhang Z. Quantum Hall phase in graphene engineered by interfacial charge coupling. NATURE NANOTECHNOLOGY 2022; 17:1272-1279. [PMID: 36411376 PMCID: PMC9747608 DOI: 10.1038/s41565-022-01248-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Accepted: 09/29/2022] [Indexed: 06/05/2023]
Abstract
The quantum Hall effect can be substantially affected by interfacial coupling between the host two-dimensional electron gases and the substrate, and has been predicted to give rise to exotic topological states. Yet the understanding of the underlying physics and the controllable engineering of this interaction remains challenging. Here we demonstrate the observation of an unusual quantum Hall effect, which differs markedly from that of the known picture, in graphene samples in contact with an antiferromagnetic insulator CrOCl equipped with dual gates. Two distinct quantum Hall phases are developed, with the Landau levels in monolayer graphene remaining intact at the conventional phase, but largely distorted for the interfacial-coupling phase. The latter quantum Hall phase is even present close to the absence of a magnetic field, with the consequential Landau quantization following a parabolic relation between the displacement field and the magnetic field. This characteristic prevails up to 100 K in a wide effective doping range from 0 to 1013 cm-2.
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Affiliation(s)
- Yaning Wang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, P. R. China
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. China
- School of Material Science and Engineering, University of Science and Technology of China, Shenyang, China
- Liaoning Academy of Materials, Shenyang, China
| | - Xiang Gao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, P. R. China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. China
| | - Kaining Yang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, P. R. China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. 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
| | - Xin Lu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
| | - Shihao Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai, 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
| | - Naijie Ren
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, P. R. China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. China
| | - Baojuan Dong
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, P. R. China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. China
| | - Yuhang Jiang
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing, 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
| | - Jun Kang
- Beijing Computational Science Research Center, Beijing, China
| | - Wenkai Lou
- State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China
| | - Jinhai Mao
- School of Physical Sciences and CAS Center for Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing, China.
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, China.
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai, 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, P. R. China.
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. China.
- Liaoning Academy of Materials, Shenyang, China.
| | - Kai Chang
- State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China.
| | - Jing Zhang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan, P. R. China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, P. R. China
| | - Zhidong Zhang
- 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, Shenyang, China
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9
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Bandurin DA, Principi A, Phinney IY, Taniguchi T, Watanabe K, Jarillo-Herrero P. Interlayer Electron-Hole Friction in Tunable Twisted Bilayer Graphene Semimetal. PHYSICAL REVIEW LETTERS 2022; 129:206802. [PMID: 36461999 DOI: 10.1103/physrevlett.129.206802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2022] [Revised: 08/22/2022] [Accepted: 10/21/2022] [Indexed: 06/17/2023]
Abstract
Charge-neutral conducting systems represent a class of materials with unusual properties governed by electron-hole (e-h) interactions. Depending on the quasiparticle statistics, band structure, and device geometry these semimetallic phases of matter can feature unconventional responses to external fields that often defy simple interpretations in terms of single-particle physics. Here we show that small-angle twisted bilayer graphene (SA TBG) offers a highly tunable system in which to explore interactions-limited electron conduction. By employing a dual-gated device architecture we tune our devices from a nondegenerate charge-neutral Dirac fluid to a compensated two-component e-h Fermi liquid where spatially separated electrons and holes experience strong mutual friction. This friction is revealed through the T^{2} resistivity that accurately follows the e-h drag theory we develop. Our results provide a textbook illustration of a smooth transition between different interaction-limited transport regimes and clarify the conduction mechanisms in charge-neutral SA TBG.
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Affiliation(s)
- D A Bandurin
- Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore
| | - A Principi
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
| | - I Y Phinney
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - K Watanabe
- Research Center for Functional Materials, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - P Jarillo-Herrero
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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10
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Piccinini G, Mišeikis V, Novelli P, Watanabe K, Taniguchi T, Polini M, Coletti C, Pezzini S. Moiré-Induced Transport in CVD-Based Small-Angle Twisted Bilayer Graphene. NANO LETTERS 2022; 22:5252-5259. [PMID: 35776918 PMCID: PMC9284678 DOI: 10.1021/acs.nanolett.2c01114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
To realize the applicative potential of 2D twistronic devices, scalable synthesis and assembly techniques need to meet stringent requirements in terms of interface cleanness and twist-angle homogeneity. Here, we show that small-angle twisted bilayer graphene assembled from separated CVD-grown graphene single-crystals can ensure high-quality transport properties, determined by a device-scale-uniform moiré potential. Via low-temperature dual-gated magnetotransport, we demonstrate the hallmarks of a 2.4°-twisted superlattice, including tunable regimes of interlayer coupling, reduced Fermi velocity, large interlayer capacitance, and density-independent Brown-Zak oscillations. The observation of these moiré-induced electrical transport features establishes CVD-based twisted bilayer graphene as an alternative to "tear-and-stack" exfoliated flakes for fundamental studies, while serving as a proof-of-concept for future large-scale assembly.
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Affiliation(s)
- Giulia Piccinini
- NEST,
Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
- Center
for Nanotechnology Innovation @NEST, Istituto
Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - Vaidotas Mišeikis
- Center
for Nanotechnology Innovation @NEST, Istituto
Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- Graphene
Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Pietro Novelli
- Istituto
Italiano di Tecnologia, Via Melen 83, 16152 Genova, Italy
| | - 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
| | - Marco Polini
- Graphene
Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
- Dipartimento
di Fisica, Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
| | - Camilla Coletti
- Center
for Nanotechnology Innovation @NEST, Istituto
Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- Graphene
Laboratories, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Sergio Pezzini
- NEST,
Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
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11
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Rickhaus P, de Vries FK, Zhu J, Portoles E, Zheng G, Masseroni M, Kurzmann A, Taniguchi T, Watanabe K, MacDonald AH, Ihn T, Ensslin K. Correlated electron-hole state in twisted double-bilayer graphene. Science 2021; 373:1257-1260. [PMID: 34516786 DOI: 10.1126/science.abc3534] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Peter Rickhaus
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | | | - Jihang Zhu
- Department of Physics, University of Texas at Austin, Austin, TX 78712, USA
| | - Elías Portoles
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Giulia Zheng
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Michele Masseroni
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Annika Kurzmann
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Allan H MacDonald
- Department of Physics, University of Texas at Austin, Austin, TX 78712, USA
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland.,Quantum Center, ETH Zürich, 8093 Zürich, Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland.,Quantum Center, ETH Zürich, 8093 Zürich, Switzerland
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12
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Slizovskiy S, Garcia-Ruiz A, Berdyugin A, Xin N, Taniguchi T, Watanabe K, Geim AK, Drummond ND, Fal’ko V. Out-of-Plane Dielectric Susceptibility of Graphene in Twistronic and Bernal Bilayers. NANO LETTERS 2021; 21:6678-6683. [PMID: 34296602 PMCID: PMC8361429 DOI: 10.1021/acs.nanolett.1c02211] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2021] [Revised: 07/14/2021] [Indexed: 05/27/2023]
Abstract
We describe how the out-of-plane dielectric polarizability of monolayer graphene influences the electrostatics of bilayer graphene-both Bernal (BLG) and twisted (tBLG). We compare the polarizability value computed using density functional theory with the output from previously published experimental data on the electrostatically controlled interlayer asymmetry potential in BLG and data on the on-layer density distribution in tBLG. We show that monolayers in tBLG are described well by polarizability αexp = 10.8 Å3 and effective out-of-plane dielectric susceptibility ϵz = 2.5, including their on-layer electron density distribution at zero magnetic field and the interlayer Landau level pinning at quantizing magnetic fields.
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Affiliation(s)
- Sergey Slizovskiy
- National
Graphene Institute, University of Manchester, Booth St.E., M13 9PL Manchester, U.K.
- Dept.
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, U.K.
| | - Aitor Garcia-Ruiz
- National
Graphene Institute, University of Manchester, Booth St.E., M13 9PL Manchester, U.K.
- Dept.
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, U.K.
| | - Alexey
I. Berdyugin
- National
Graphene Institute, University of Manchester, Booth St.E., M13 9PL Manchester, U.K.
- Dept.
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, U.K.
| | - Na Xin
- National
Graphene Institute, University of Manchester, Booth St.E., M13 9PL Manchester, U.K.
- Dept.
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, U.K.
| | - Takashi Taniguchi
- National
Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- National
Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Andre K. Geim
- National
Graphene Institute, University of Manchester, Booth St.E., M13 9PL Manchester, U.K.
- Dept.
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, U.K.
| | - Neil D. Drummond
- Department
of Physics, Lancaster University, Lancaster LA1 4YB, U.K.
| | - Vladimir
I. Fal’ko
- National
Graphene Institute, University of Manchester, Booth St.E., M13 9PL Manchester, U.K.
- Dept.
of Physics & Astronomy, University of
Manchester, Manchester M13 9PL, U.K.
- Henry
Royce Institute for Advanced Materials, Manchester M13 9PL, U.K.
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13
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Phinney IY, Bandurin DA, Collignon C, Dmitriev IA, Taniguchi T, Watanabe K, Jarillo-Herrero P. Strong Interminivalley Scattering in Twisted Bilayer Graphene Revealed by High-Temperature Magneto-Oscillations. PHYSICAL REVIEW LETTERS 2021; 127:056802. [PMID: 34397232 DOI: 10.1103/physrevlett.127.056802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 06/29/2021] [Indexed: 06/13/2023]
Abstract
Twisted bilayer graphene (TBG) provides an example of a system in which the interplay of interlayer interactions and superlattice structure impacts electron transport in a variety of nontrivial ways and gives rise to a plethora of interesting effects. Understanding the mechanisms of electron scattering in TBG has, however, proven challenging, raising many questions about the origins of resistivity in this system. Here we show that TBG exhibits high-temperature magneto-oscillations originating from the scattering of charge carriers between TBG minivalleys. The amplitude of these oscillations reveals that interminivalley scattering is strong, and its characteristic timescale is comparable to that of its intraminivalley counterpart. Furthermore, by exploring the temperature dependence of these oscillations, we estimate the electron-electron collision rate in TBG and find that it exceeds that of monolayer graphene. Our study demonstrates the consequences of the relatively small size of the superlattice Brillouin zone and Fermi velocity reduction on lateral transport in TBG.
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Affiliation(s)
- I Y Phinney
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - D A Bandurin
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - C Collignon
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - I A Dmitriev
- Physics Department, University of Regensburg, 93040, Regensburg, Germany
- Ioffe Institute, 194021 St. Petersburg, Russia
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - K Watanabe
- Research Center for Functional Materials, National Institute of Material Science, Tsukuba 305-0044, Japan
| | - P Jarillo-Herrero
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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14
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Kim Y, Moon P, Watanabe K, Taniguchi T, Smet JH. Odd Integer Quantum Hall States with Interlayer Coherence in Twisted Bilayer Graphene. NANO LETTERS 2021; 21:4249-4254. [PMID: 33955215 PMCID: PMC8289309 DOI: 10.1021/acs.nanolett.1c00360] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Revised: 05/04/2021] [Indexed: 06/12/2023]
Abstract
We report on the quantum Hall effect in two stacked graphene layers rotated by 2°. The tunneling strength among the layers can be varied from very weak to strong via the mechanism of magnetic breakdown when tuning the density. Odd-integer quantum Hall physics is not anticipated in the regime of suppressed tunneling for balanced layer densities, yet it is observed. We interpret this as a signature of Coulomb interaction induced interlayer coherence and Bose-Einstein condensation of excitons that form at half filling of each layer. A density imbalance gives rise to reentrant behavior due to a phase transition from the interlayer coherent state to incompressible behavior caused by simultaneous condensation of both layers in different quantum Hall states. With increasing overall density, magnetic breakdown gains the upper hand. As a consequence of the enhanced interlayer tunneling, the interlayer coherent state and the phase transition vanish.
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Affiliation(s)
- Youngwook Kim
- Max-Planck-Institut
für Festköperforschung, 70569 Stuttgart, Germany
- Department
of Emerging Materials Science, DGIST, 42988 Daegu, Korea
| | - Pilkyung Moon
- Arts
and Sciences, NYU Shanghai, Shanghai 200122, China and NYU-ECNU Institute of Physics at NYU Shanghai, Shanghai 200062, China
| | - Kenji Watanabe
- Research
Center for Functional Materials, National
Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International
Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan
| | - Jurgen H. Smet
- Max-Planck-Institut
für Festköperforschung, 70569 Stuttgart, Germany
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15
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Majchrzak P, Muzzio R, Jones AJH, Curcio D, Volckaert K, Biswas D, Gobbo J, Singh S, Robinson JT, Watanabe K, Taniguchi T, Kim TK, Cacho C, Miwa JA, Hofmann P, Katoch J, Ulstrup S. In Operando Angle‐Resolved Photoemission Spectroscopy with Nanoscale Spatial Resolution: Spatial Mapping of the Electronic Structure of Twisted Bilayer Graphene. SMALL SCIENCE 2021. [DOI: 10.1002/smsc.202000075] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Affiliation(s)
- Paulina Majchrzak
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Ryan Muzzio
- Department of Physics Carnegie Mellon University Pittsburgh, Pennsylvania 15213 USA
| | - Alfred J. H. Jones
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Davide Curcio
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Klara Volckaert
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Deepnarayan Biswas
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Jacob Gobbo
- Department of Physics Carnegie Mellon University Pittsburgh, Pennsylvania 15213 USA
| | - Simranjeet Singh
- Department of Physics Carnegie Mellon University Pittsburgh, Pennsylvania 15213 USA
| | - Jeremy T. Robinson
- Electronics Science and Technology Division US Naval Research Laboratory Washington D.C 20375 USA
| | - 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
| | - Timur K. Kim
- Diamond Light Source Division of Science Didcot United Kingdom
| | - Cephise Cacho
- Diamond Light Source Division of Science Didcot United Kingdom
| | - Jill A. Miwa
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Philip Hofmann
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
| | - Jyoti Katoch
- Department of Physics Carnegie Mellon University Pittsburgh, Pennsylvania 15213 USA
| | - Søren Ulstrup
- Department of Physics and Astronomy Aarhus University 8000 Aarhus C Denmark
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16
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Mahapatra PS, Ghawri B, Garg M, Mandal S, Watanabe K, Taniguchi T, Jain M, Mukerjee S, Ghosh A. Misorientation-Controlled Cross-Plane Thermoelectricity in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2020; 125:226802. [PMID: 33315457 DOI: 10.1103/physrevlett.125.226802] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 05/08/2020] [Accepted: 10/15/2020] [Indexed: 06/12/2023]
Abstract
The introduction of "twist" or relative rotation between two atomically thin van der Waals membranes gives rise to periodic moiré potential, leading to a substantial alteration of the band structure of the planar assembly. While most of the recent experiments primarily focus on the electronic-band hybridization by probing in-plane transport properties, here we report out-of-plane thermoelectric measurements across the van der Waals gap in twisted bilayer graphene, which exhibits an interplay of twist-dependent interlayer electronic and phononic hybridization. We show that at large twist angles, the thermopower is entirely driven by a novel phonon-drag effect at subnanometer scale, while the electronic component of the thermopower is recovered only when the misorientation between the layers is reduced to <6°. Our experiment shows that cross-plane thermoelectricity at low angles is exceptionally sensitive to the nature of band dispersion and may provide fundamental insights into the coherence of electronic states in twisted bilayer graphene.
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Affiliation(s)
| | - Bhaskar Ghawri
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - Manjari Garg
- Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India
| | - Shinjan Mandal
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - K Watanabe
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - Manish Jain
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - Subroto Mukerjee
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
| | - Arindam Ghosh
- Department of Physics, Indian Institute of Science, Bangalore 560 012, India
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17
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Keren I, Dvir T, Zalic A, Iluz A, LeBoeuf D, Watanabe K, Taniguchi T, Steinberg H. Quantum-dot assisted spectroscopy of degeneracy-lifted Landau levels in graphene. Nat Commun 2020; 11:3408. [PMID: 32641683 PMCID: PMC7343833 DOI: 10.1038/s41467-020-17225-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Accepted: 06/17/2020] [Indexed: 11/09/2022] Open
Abstract
Energy spectroscopy of strongly interacting phases requires probes which minimize screening while retaining spectral resolution and local sensitivity. Here, we demonstrate that such probes can be realized using atomic sized quantum dots bound to defects in hexagonal Boron Nitride tunnel barriers, placed at nanometric distance from graphene. With dot energies capacitively tuned by a planar graphite electrode, dot-assisted tunneling becomes highly sensitive to the graphene excitation spectrum. The spectra track the onset of degeneracy lifting with magnetic field at the ground state, and at unoccupied excited states, revealing symmetry-broken gaps which develop steeply with magnetic field - corresponding to Landé g factors as high as 160. Measured up to B = 33 T, spectra exhibit a primary energy split between spin-polarized excited states, and a secondary spin-dependent valley-split. Our results show that defect dots probe the spectra while minimizing local screening, and are thus exceptionally sensitive to interacting states.
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Affiliation(s)
- Itai Keren
- Racah Institute of Physics, The Hebrew University, 91904, Jerusalem, Israel
| | - Tom Dvir
- Racah Institute of Physics, The Hebrew University, 91904, Jerusalem, Israel
| | - Ayelet Zalic
- Racah Institute of Physics, The Hebrew University, 91904, Jerusalem, Israel
| | - Amir Iluz
- Racah Institute of Physics, The Hebrew University, 91904, Jerusalem, Israel
| | - David LeBoeuf
- LNCMI, Centre National de la Recherche Scientifique, EMFL, Université Grenoble Alpes, INSA Toulouse, Université Toulouse Paul Sabatier, Grenoble, France
| | - Kenji Watanabe
- National Institute for Material Science, 1-1 Namiki, Tsukaba, 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Material Science, 1-1 Namiki, Tsukaba, 305-0044, Japan
| | - Hadar Steinberg
- Racah Institute of Physics, The Hebrew University, 91904, Jerusalem, Israel.
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18
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Kang P, Zhang W, Michaud-Rioux V, Wang X, Yun J, Guo H. Twistronics in tensile strained bilayer black phosphorus. NANOSCALE 2020; 12:12909-12916. [PMID: 32525178 DOI: 10.1039/d0nr02179b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this work, by performing state-of-the-art first-principles methods combined with molecular dynamic (MD) simulation, we theoretically investigate the electronic and mechanical behaviours of small-angle twisted bilayer black phosphorus (tbBP) under uniaxial tensile deformation. Twistronics, namely the regulation of electronic properties by Moiré physics, is demonstrated as the gene - the most crucial factor dominating not only electronic behaviour but also mechanical behaviour of tensile deformed tbBP. Compared to untwisted few-layer black phosphorus (utBP) with strong electronic sensitivity to geometric deformation, the existence of Moiré patterns in tbBP leads to spatial electronic localization, giving rise to the conservation of direct band gaps and stability of phonon limited carrier mobility under tensile deformation along the armchair direction. Moreover, during the fracture failure process, the nucleation of micro-cracks is preferentially detected at the transitional pattern boundary areas in tbBP, which could be attributed to the intra-layer maldistribution of mechanical strengths in Moiré superlattices. The explorations of twistronics in tensile strained bilayer black phosphorus contribute to the better understanding of such Moiré superlattice structures and provide insights for the design of new 2D van der Waals heterostructures in flexible nano-electronic devices.
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Affiliation(s)
- Peng Kang
- Center for the Physics of Materials and Department of Physics, McGill University, Montreal, Quebec H3A 2 T8, Canada.
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19
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Nimbalkar A, Kim H. Opportunities and Challenges in Twisted Bilayer Graphene: A Review. NANO-MICRO LETTERS 2020; 12:126. [PMID: 34138115 PMCID: PMC7770697 DOI: 10.1007/s40820-020-00464-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 05/19/2020] [Indexed: 05/26/2023]
Abstract
Two-dimensional (2D) materials exhibit enhanced physical, chemical, electronic, and optical properties when compared to those of bulk materials. Graphene demands significant attention due to its superior physical and electronic characteristics among different types of 2D materials. The bilayer graphene is fabricated by the stacking of the two monolayers of graphene. The twisted bilayer graphene (tBLG) superlattice is formed when these layers are twisted at a small angle. The presence of disorders and interlayer interactions in tBLG enhances several characteristics, including the optical and electrical properties. The studies on twisted bilayer graphene have been exciting and challenging thus far, especially after superconductivity was reported in tBLG at the magic angle. This article reviews the current progress in the fabrication techniques of twisted bilayer graphene and its twisting angle-dependent properties.
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Affiliation(s)
- Amol Nimbalkar
- Division of Biotechnology, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, 42988, Republic of Korea
| | - Hyunmin Kim
- Division of Biotechnology, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, 42988, Republic of Korea.
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20
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Pezzini S, Mišeikis V, Piccinini G, Forti S, Pace S, Engelke R, Rossella F, Watanabe K, Taniguchi T, Kim P, Coletti C. 30°-Twisted Bilayer Graphene Quasicrystals from Chemical Vapor Deposition. NANO LETTERS 2020; 20:3313-3319. [PMID: 32297749 DOI: 10.1021/acs.nanolett.0c00172] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The artificial stacking of atomically thin crystals suffers from intrinsic limitations in terms of control and reproducibility of the relative orientation of exfoliated flakes. This drawback is particularly severe when the properties of the system critically depends on the twist angle, as in the case of the dodecagonal quasicrystal formed by two graphene layers rotated by 30°. Here we show that large-area 30°-rotated bilayer graphene can be grown deterministically by chemical vapor deposition on Cu, eliminating the need of artificial assembly. The quasicrystals are easily transferred to arbitrary substrates and integrated in high-quality hexagonal boron nitride-encapsulated heterostructures, which we process into dual-gated devices exhibiting carrier mobility up to 105 cm2/(V s). From low-temperature magnetotransport, we find that the graphene quasicrystals effectively behave as uncoupled graphene layers, showing 8-fold degenerate quantum Hall states. This result indicates that the Dirac cones replica detected by previous photoemission experiments do not contribute to the electrical transport.
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Affiliation(s)
- Sergio Pezzini
- Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Vaidotas Mišeikis
- Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Giulia Piccinini
- Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- NEST, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - Stiven Forti
- Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - Simona Pace
- Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Rebecca Engelke
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Francesco Rossella
- NEST, Scuola Normale Superiore, Piazza San Silvestro 12, 56127 Pisa, Italy
- NEST, Istituto Nanoscienze-CNR, Piazza San Silvestro 12, 56127 Pisa, Italy
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
| | - Camilla Coletti
- Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
- Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
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21
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Berdyugin AI, Tsim B, Kumaravadivel P, Xu SG, Ceferino A, Knothe A, Kumar RK, Taniguchi T, Watanabe K, Geim AK, Grigorieva IV, Fal’ko VI. Minibands in twisted bilayer graphene probed by magnetic focusing. SCIENCE ADVANCES 2020; 6:eaay7838. [PMID: 32494602 PMCID: PMC7164947 DOI: 10.1126/sciadv.aay7838] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 01/22/2020] [Indexed: 05/25/2023]
Abstract
Magnetic fields force ballistic electrons injected from a narrow contact to move along skipping orbits and form caustics. This leads to pronounced resistance peaks at nearby voltage probes as electrons are effectively focused inside them, a phenomenon known as magnetic focusing. This can be used not only for the demonstration of ballistic transport but also to study the electronic structure of metals. Here, we use magnetic focusing to probe narrowbands in graphene bilayers twisted at ~2°. Their minibands are found to support long-range ballistic transport limited at low temperatures by intrinsic electron-electron scattering. A voltage bias between the layers causes strong minivalley splitting and allows selective focusing for different minivalleys, which is of interest for using this degree of freedom in frequently discussed valleytronics.
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Affiliation(s)
- A. I. Berdyugin
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
| | - B. Tsim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - P. Kumaravadivel
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - S. G. Xu
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - A. Ceferino
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - A. Knothe
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - R. Krishna Kumar
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - T. Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - K. Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - A. K. Geim
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
| | - I. V. Grigorieva
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Manchester M13 9PL, UK
| | - V. I. Fal’ko
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
- National Graphene Institute, University of Manchester, Manchester M13 9PL, UK
- Henry Royce Institute for Advanced Materials, Manchester M13 9PL, UK
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22
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Rickhaus P, Liu MH, Kurpas M, Kurzmann A, Lee Y, Overweg H, Eich M, Pisoni R, Taniguchi T, Watanabe K, Richter K, Ensslin K, Ihn T. The electronic thickness of graphene. SCIENCE ADVANCES 2020; 6:eaay8409. [PMID: 32201727 PMCID: PMC7069711 DOI: 10.1126/sciadv.aay8409] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 12/16/2019] [Indexed: 05/31/2023]
Abstract
When two dimensional crystals are atomically close, their finite thickness becomes relevant. Using transport measurements, we investigate the electrostatics of two graphene layers, twisted by θ = 22° such that the layers are decoupled by the huge momentum mismatch between the K and K' points of the two layers. We observe a splitting of the zero-density lines of the two layers with increasing interlayer energy difference. This splitting is given by the ratio of single-layer quantum capacitance over interlayer capacitance C m and is therefore suited to extract C m. We explain the large observed value of C m by considering the finite dielectric thickness d g of each graphene layer and determine d g ≈ 2.6 Å. In a second experiment, we map out the entire density range with a Fabry-Pérot resonator. We can precisely measure the Fermi wavelength λ in each layer, showing that the layers are decoupled. Our findings are reproduced using tight-binding calculations.
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Affiliation(s)
- Peter Rickhaus
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Ming-Hao Liu
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
| | - Marcin Kurpas
- Institute of Physics, University of Silesia in Katowice, 41-500 Chorzów, Poland
| | - Annika Kurzmann
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Yongjin Lee
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Hiske Overweg
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
- Microsoft Research Cambridge, Cambridge, UK
| | - Marius Eich
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Riccardo Pisoni
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Klaus Richter
- Institute of Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - Klaus Ensslin
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Thomas Ihn
- Solid State Physics Laboratory, ETH Zürich, CH-8093 Zürich, Switzerland
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23
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Deng B, Wang B, Li N, Li R, Wang Y, Tang J, Fu Q, Tian Z, Gao P, Xue J, Peng H. Interlayer Decoupling in 30° Twisted Bilayer Graphene Quasicrystal. ACS NANO 2020; 14:1656-1664. [PMID: 31961130 DOI: 10.1021/acsnano.9b07091] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Stacking order has a strong influence on the coupling between the two layers of twisted bilayer graphene (BLG), which in turn determines its physical properties. Here, we report the investigation of the interlayer coupling of the epitaxially grown single-crystal 30°-twisted BLG on Cu(111) at the atomic scale. The stacking order and morphology of BLG is controlled by a rationally designed two-step growth process, that is, the thermodynamically controlled nucleation and kinetically controlled growth. The crystal structure of the 30°-twisted bilayer graphene (30°-tBLG) is determined to have quasicrystal-like symmetry. The electronic properties and interlayer coupling of the 30°-tBLG are investigated using scanning tunneling microscopy and spectroscopy. The energy-dependent local density of states with in situ electrostatic doping shows that the electronic states in two graphene layers are decoupled near the Dirac point. A linear dispersion originated from the constituent graphene monolayers is discovered with doubled degeneracy. This study contributes to controlled growth of twist-angle-defined BLG and provides insights on the electronic properties and interlayer coupling in this intriguing system.
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Affiliation(s)
- Bing Deng
- Center for Nanochemistry (CNC), Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences (BNLMS), College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , China
| | - Binbin Wang
- School of Physical Science and Technology , ShanghaiTech University , Shanghai 201210 , China
| | - Ning Li
- International Center for Quantum Materials, and Electron Microscopy Laboratory, School of Physics , Peking University , Beijing 100871 , China
- Collaborative Innovation Center of Quantum Matter , Beijing 100871 , China
| | - Rongtan Li
- State Key Laboratory of Catalysis, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM) , Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023 , China
| | - Yani Wang
- Center for Nanochemistry (CNC), Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences (BNLMS), College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , China
| | - Jilin Tang
- Center for Nanochemistry (CNC), Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences (BNLMS), College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , China
- Academy for Advanced Interdisciplinary Studies , Peking University , Beijing 100871 , China
| | - Qiang Fu
- State Key Laboratory of Catalysis, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM) , Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023 , China
| | - Zhen Tian
- School of Physical Science and Technology , ShanghaiTech University , Shanghai 201210 , China
| | - Peng Gao
- International Center for Quantum Materials, and Electron Microscopy Laboratory, School of Physics , Peking University , Beijing 100871 , China
- Collaborative Innovation Center of Quantum Matter , Beijing 100871 , China
| | - Jiamin Xue
- School of Physical Science and Technology , ShanghaiTech University , Shanghai 201210 , China
| | - Hailin Peng
- Center for Nanochemistry (CNC), Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences (BNLMS), College of Chemistry and Molecular Engineering , Peking University , Beijing 100871 , China
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24
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Rickhaus P, Zheng G, Lado JL, Lee Y, Kurzmann A, Eich M, Pisoni R, Tong C, Garreis R, Gold C, Masseroni M, Taniguchi T, Wantanabe K, Ihn T, Ensslin K. Gap Opening in Twisted Double Bilayer Graphene by Crystal Fields. NANO LETTERS 2019; 19:8821-8828. [PMID: 31670969 DOI: 10.1021/acs.nanolett.9b03660] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Crystal fields occur due to a potential difference between chemically different atomic species. In van der Waals heterostructures such fields are naturally present perpendicular to the planes. It has been realized recently that twisted graphene multilayers provide powerful playgrounds to engineer electronic properties by the number of layers, the twist angle, applied electric biases, electronic interactions, and elastic relaxations, but crystal fields have not received the attention they deserve. Here, we show that the band structure of large-angle twisted double bilayer graphene is strongly modified by crystal fields. In particular, we experimentally demonstrate that twisted double bilayer graphene, encapsulated between hBN layers, exhibits an intrinsic band gap. By the application of an external field, the gaps in the individual bilayers can be closed, allowing to determine the crystal fields. We find that crystal fields point from the outer to the inner layers with strengths in the bottom/top bilayer [Formula: see text] = 0.13 V/nm ≈ [Formula: see text] = 0.12 V/nm. We show both by means of first-principles calculations and low energy models that crystal fields open a band gap in the ground state. Our results put forward a physical scenario in which a crystal field effect in carbon substantially impacts the low energy properties of twisted double bilayer graphene, suggesting that such contributions must be taken into account in other regimes to faithfully predict the electronic properties of twisted graphene multilayers.
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Affiliation(s)
- Peter Rickhaus
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Giulia Zheng
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Jose L Lado
- Department of Applied Physics , Aalto University , Espoo , Finland
- Institute for Theoretical Physics , ETH Zurich , 8093 Zurich , Switzerland
| | - Yongjin Lee
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Annika Kurzmann
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Marius Eich
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Riccardo Pisoni
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Chuyao Tong
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Rebekka Garreis
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Carolin Gold
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Michele Masseroni
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Takashi Taniguchi
- National Institute for Material Science , 1-1 Namiki , Tsukuba 305-0044 , Japan
| | - Kenji Wantanabe
- National Institute for Material Science , 1-1 Namiki , Tsukuba 305-0044 , Japan
| | - Thomas Ihn
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
| | - Klaus Ensslin
- Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland
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25
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Bessler R, Duerig U, Koren E. The dielectric constant of a bilayer graphene interface. NANOSCALE ADVANCES 2019; 1:1702-1706. [PMID: 36134207 PMCID: PMC9417051 DOI: 10.1039/c8na00350e] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 03/07/2019] [Indexed: 05/30/2023]
Abstract
The interlayer relative dielectric constant, ε r, of 2-dimensional (2D) materials in general and graphitic materials in particular is one of their most important physical properties, especially for electronic applications. In this work, we study the electromechanical actuation of nano-scale graphitic contacts. We find that beside the adhesive forces there are capacitive forces that scale parabolically with the potential drop across the sheared interface. We use this phenomena to measure the intrinsic dielectric constant of the bilayer graphene interface i.e. ε r = 6 ± 2, which is in perfect agreement with recent theoretical predictions for multi-layer graphene structures. Our method can be generally used to extract the dielectric properties of 2D materials systems and interfaces and our results pave the way for utilizing graphitic and other 2D materials in electromechanical based applications.
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Affiliation(s)
- Ron Bessler
- Department of Materials Science and Engineering, The Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology 3200003 Haifa Israel
| | - Urs Duerig
- SwissLitho AG Technopark 8005 Zurich Switzerland
| | - Elad Koren
- Department of Materials Science and Engineering, The Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology 3200003 Haifa Israel
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26
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Yoo H, Engelke R, Carr S, Fang S, Zhang K, Cazeaux P, Sung SH, Hovden R, Tsen AW, Taniguchi T, Watanabe K, Yi GC, Kim M, Luskin M, Tadmor EB, Kaxiras E, Kim P. Atomic and electronic reconstruction at the van der Waals interface in twisted bilayer graphene. NATURE MATERIALS 2019; 18:448-453. [PMID: 30988451 DOI: 10.1038/s41563-019-0346-z] [Citation(s) in RCA: 198] [Impact Index Per Article: 39.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 03/15/2019] [Indexed: 05/12/2023]
Abstract
Control of the interlayer twist angle in two-dimensional van der Waals (vdW) heterostructures enables one to engineer a quasiperiodic moiré superlattice of tunable length scale1-8. In twisted bilayer graphene, the simple moiré superlattice band description suggests that the electronic bandwidth can be tuned to be comparable to the vdW interlayer interaction at a 'magic angle'9, exhibiting strongly correlated behaviour. However, the vdW interlayer interaction can also cause significant structural reconstruction at the interface by favouring interlayer commensurability, which competes with the intralayer lattice distortion10-16. Here we report atomic-scale reconstruction in twisted bilayer graphene and its effect on the electronic structure. We find a gradual transition from an incommensurate moiré structure to an array of commensurate domains with soliton boundaries as we decrease the twist angle across the characteristic crossover angle, θc ≈ 1°. In the solitonic regime (θ < θc) where the atomic and electronic reconstruction become significant, a simple moiré band description breaks down and the secondary Dirac bands appear. On applying a transverse electric field, we observe electronic transport along the network of one-dimensional topological channels that surround the alternating triangular gapped domains. Atomic and electronic reconstruction at the vdW interface provide a new pathway to engineer the system with continuous tunability.
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Affiliation(s)
- Hyobin Yoo
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Rebecca Engelke
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Stephen Carr
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Shiang Fang
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Kuan Zhang
- Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN, USA
| | - Paul Cazeaux
- Department of Mathematics, University of Kansas, Lawrence, KS, USA
| | - Suk Hyun Sung
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Robert Hovden
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA
| | - Adam W Tsen
- Institute for Quantum Computing and Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada
| | | | - Kenji Watanabe
- National Institute for Materials Science, Ibaraki, Japan
| | - Gyu-Chul Yi
- Department of Physics and Astronomy, Seoul National University, Seoul, Republic of Korea
| | - Miyoung Kim
- Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea
| | - Mitchell Luskin
- School of Mathematics, University of Minnesota, Minneapolis, MN, USA
| | - Ellad B Tadmor
- Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN, USA
| | - Efthimios Kaxiras
- Department of Physics, Harvard University, Cambridge, MA, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, MA, USA.
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27
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González J, Stauber T. Kohn-Luttinger Superconductivity in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2019; 122:026801. [PMID: 30720323 DOI: 10.1103/physrevlett.122.026801] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Indexed: 05/27/2023]
Abstract
We show that the recently observed superconductivity in twisted bilayer graphene (TBG) can be explained as a consequence of the Kohn-Luttinger (KL) instability which leads to an effective attraction between electrons with originally repulsive interaction. Usually, the KL instability takes place at extremely low energy scales, but in TBG, a doubling and subsequent strong coupling of the van Hove singularities (vHS) in the electronic spectrum occurs as the magic angle is approached, leading to extended saddle points in the highest valence band with almost perfect nesting between states belonging to different valleys. The highly anisotropic screening induces an effective attraction in a p-wave channel with odd parity under the exchange of the two disjoined patches of the Fermi line. We also predict the appearance of a spin-density wave instability, adjacent to the superconducting phase, and the opening of a gap in the electronic spectrum from the condensation of spins with wave vector corresponding to the nesting vector close to the vHS.
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Affiliation(s)
- J González
- Instituto de Estructura de la Materia, CSIC, E-28006 Madrid, Spain
| | - T Stauber
- Materials Science Factory, Instituto de Ciencia de Materiales de Madrid, CSIC, E-28049 Madrid, Spain
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28
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Kolumbus Y, Zalic A, Fardian-Melamed N, Barkay Z, Rotem D, Porath D, Steinberg H. Crystallographic orientation errors in mechanical exfoliation. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:475704. [PMID: 30398169 DOI: 10.1088/1361-648x/aae877] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We evaluate the effect of mechanical exfoliation of van der Waals materials on crystallographic orientations of the resulting flakes. Flakes originating from a single crystal of graphite, whose orientation is confirmed using STM, are studied using facet orientations and electron back-scatter diffraction (EBSD). While facets exhibit a wide distribution of angles after a single round of exfoliation ([Formula: see text]), EBSD shows that the true crystallographic orientations are more narrowly distributed ([Formula: see text]), and facets have an approximately [Formula: see text] error from the true orientation. Furthermore, we find that the majority of graphite fractures are along armchair lines, and that the cleavage process results in an increase of the zigzag lines portion. Our results place values on the rotation caused by a single round of the exfoliation process, and suggest that when a 1-2 degree precision is necessary, the orientation of a flake can be gauged by the orientation of the macroscopic single crystal from which it was exfoliated.
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Affiliation(s)
- Y Kolumbus
- Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 9190401 Israel
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29
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Huang S, Kim K, Efimkin DK, Lovorn T, Taniguchi T, Watanabe K, MacDonald AH, Tutuc E, LeRoy BJ. Topologically Protected Helical States in Minimally Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2018; 121:037702. [PMID: 30085814 DOI: 10.1103/physrevlett.121.037702] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Indexed: 06/08/2023]
Abstract
In minimally twisted bilayer graphene, a moiré pattern consisting of AB and BA stacking regions separated by domain walls forms. These domain walls are predicted to support counterpropogating topologically protected helical (TPH) edge states when the AB and BA regions are gapped. We fabricate designer moiré crystals with wavelengths longer than 50 nm and demonstrate the emergence of TPH states on the domain wall network by scanning tunneling spectroscopy measurements. We observe a double-line profile of the TPH states on the domain walls, only occurring when the AB and BA regions are gapped. Our results demonstrate a practical and flexible method for TPH state network construction.
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Affiliation(s)
- Shengqiang Huang
- Physics Department, University of Arizona, Tucson, Arizona 85721, USA
| | - Kyounghwan Kim
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, USA
| | - Dmitry K Efimkin
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Timothy Lovorn
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki Tsukuba Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki Tsukuba Ibaraki 305-0044, Japan
| | - Allan H MacDonald
- Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
| | - Emanuel Tutuc
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, USA
| | - Brian J LeRoy
- Physics Department, University of Arizona, Tucson, Arizona 85721, USA
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30
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Ahn SJ, Moon P, Kim TH, Kim HW, Shin HC, Kim EH, Cha HW, Kahng SJ, Kim P, Koshino M, Son YW, Yang CW, Ahn JR. Dirac electrons in a dodecagonal graphene quasicrystal. Science 2018; 361:782-786. [PMID: 29954987 DOI: 10.1126/science.aar8412] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Accepted: 06/19/2018] [Indexed: 01/29/2023]
Abstract
Quantum states of quasiparticles in solids are dictated by symmetry. We have experimentally demonstrated quantum states of Dirac electrons in a two-dimensional quasicrystal without translational symmetry. A dodecagonal quasicrystalline order was realized by epitaxial growth of twisted bilayer graphene rotated exactly 30°. We grew the graphene quasicrystal up to a millimeter scale on a silicon carbide surface while maintaining the single rotation angle over an entire sample and successfully isolated the quasicrystal from a substrate, demonstrating its structural and chemical stability under ambient conditions. Multiple Dirac cones replicated with the 12-fold rotational symmetry were observed in angle-resolved photoemission spectra, which revealed anomalous strong interlayer coupling with quasi-periodicity. Our study provides a way to explore physical properties of relativistic fermions with controllable quasicrystalline orders.
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Affiliation(s)
- Sung Joon Ahn
- Department of Physics and SAINT, Sungkyunkwan University, Suwon, Republic of Korea
| | - Pilkyung Moon
- New York University and NYU-ECNU Institute of Physics at NYU Shanghai, Shanghai, China.,Department of Physics, New York University, New York, NY, USA
| | - Tae-Hoon Kim
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | - Hyun-Woo Kim
- Department of Physics and SAINT, Sungkyunkwan University, Suwon, Republic of Korea
| | - Ha-Chul Shin
- Department of Physics and SAINT, Sungkyunkwan University, Suwon, Republic of Korea
| | - Eun Hye Kim
- Department of Physics and SAINT, Sungkyunkwan University, Suwon, Republic of Korea
| | - Hyun Woo Cha
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Republic of Korea
| | - Se-Jong Kahng
- Department of Physics, Korea University, Seoul, Republic of Korea
| | - Philip Kim
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Mikito Koshino
- Department of Physics, Osaka University, Machikaneyama, Toyonaka, Japan
| | - Young-Woo Son
- Korea Institute for Advanced Study, Seoul, Republic of Korea.
| | - Cheol-Woong Yang
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Republic of Korea.
| | - Joung Real Ahn
- Department of Physics and SAINT, Sungkyunkwan University, Suwon, Republic of Korea. .,Samsung-SKKU Graphene Center, Sungkyunkwan University, Suwon, Republic of Korea
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31
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Wu JB, Lin ML, Cong X, Liu HN, Tan PH. Raman spectroscopy of graphene-based materials and its applications in related devices. Chem Soc Rev 2018; 47:1822-1873. [PMID: 29368764 DOI: 10.1039/c6cs00915h] [Citation(s) in RCA: 522] [Impact Index Per Article: 87.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Graphene-based materials exhibit remarkable electronic, optical, and mechanical properties, which has resulted in both high scientific interest and huge potential for a variety of applications. Furthermore, the family of graphene-based materials is growing because of developments in preparation methods. Raman spectroscopy is a versatile tool to identify and characterize the chemical and physical properties of these materials, both at the laboratory and mass-production scale. This technique is so important that most of the papers published concerning these materials contain at least one Raman spectrum. Thus, here, we systematically review the developments in Raman spectroscopy of graphene-based materials from both fundamental research and practical (i.e., device applications) perspectives. We describe the essential Raman scattering processes of the entire first- and second-order modes in intrinsic graphene. Furthermore, the shear, layer-breathing, G and 2D modes of multilayer graphene with different stacking orders are discussed. Techniques to determine the number of graphene layers, to probe resonance Raman spectra of monolayer and multilayer graphenes and to obtain Raman images of graphene-based materials are also presented. The extensive capabilities of Raman spectroscopy for the investigation of the fundamental properties of graphene under external perturbations are described, which have also been extended to other graphene-based materials, such as graphene quantum dots, carbon dots, graphene oxide, nanoribbons, chemical vapor deposition-grown and SiC epitaxially grown graphene flakes, composites, and graphene-based van der Waals heterostructures. These fundamental properties have been used to probe the states, effects, and mechanisms of graphene materials present in the related heterostructures and devices. We hope that this review will be beneficial in all the aspects of graphene investigations, from basic research to material synthesis and device applications.
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Affiliation(s)
- Jiang-Bin Wu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
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32
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Abstract
By combining optical imaging, Raman spectroscopy, kelvin probe force microscopy (KFPM), and photoemission electron microscopy (PEEM), we show that graphene’s layer orientation, as well as layer thickness, measurably changes the surface potential (Φ). Detailed mapping of variable-thickness, rotationally-faulted graphene films allows us to correlate Φ with specific morphological features. Using KPFM and PEEM we measure ΔΦ up to 39 mV for layers with different twist angles, while ΔΦ ranges from 36–129 mV for different layer thicknesses. The surface potential between different twist angles or layer thicknesses is measured at the KPFM instrument resolution of ≤ 200 nm. The PEEM measured work function of 4.4 eV for graphene is consistent with doping levels on the order of 1012cm−2. We find that Φ scales linearly with Raman G-peak wavenumber shift (slope = 22.2 mV/cm−1) for all layers and twist angles, which is consistent with doping-dependent changes to graphene’s Fermi energy in the ‘high’ doping limit. Our results here emphasize that layer orientation is equally important as layer thickness when designing multilayer two-dimensional systems where surface potential is considered.
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33
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Pan C, Wu Y, Cheng B, Che S, Taniguchi T, Watanabe K, Lau CN, Bockrath M. Layer Polarizability and Easy-Axis Quantum Hall Ferromagnetism in Bilayer Graphene. NANO LETTERS 2017; 17:3416-3420. [PMID: 28429942 DOI: 10.1021/acs.nanolett.7b00197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We report magnetotransport measurements of graphene bilayers at large perpendicular electric displacement fields, up to ∼1.5 V/nm, where we observe crossings between Landau levels with different orbital quantum numbers. The displacement fields at the studied crossings are primarily determined by energy shifts originating from the Landau level layer polarizability or polarization. Despite decreasing Landau level spacing with energy, successive crossings occur at larger displacement fields, resulting from decreasing polarizability with orbital quantum number. For particular crossings we observe resistivity hysteresis in displacement field, indicating the presence of a first-order transition between states exhibiting easy-axis quantum Hall ferromagnetism.
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Affiliation(s)
- C Pan
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - Y Wu
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - B Cheng
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - S Che
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - T Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan
| | - K Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science , Tsukuba, Ibaraki 305-0044, Japan
| | - C N Lau
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
| | - M Bockrath
- Department of Physics and Astronomy, University of California , Riverside, California 92521, United States
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34
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Banerjee A, Rai A, Majhi K, Barman SR, Ganesan R, Anil Kumar PS. Intermediate stages of surface state formation and collapse of topological protection to transport in Bi 2Se 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:185001. [PMID: 28350542 DOI: 10.1088/1361-648x/aa666a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Surface states consisting of helical Dirac fermions have been extensively studied in three-dimensional topological insulators. Yet, experiments to date have only investigated fully formed topological surface states (TSS) and it is not known whether preformed or partially formed surface states can exist or what properties they could potentially host. Here, by decorating thin films of Bi2Se3 with nanosized islands of the same material, we show for the first time that not only can surface states exist in various intermediate stages of formation but they exhibit unique properties not accessible in fully formed TSS. These include tunability of the Dirac cone mass, vertical migration of the surface state wave-function and the appearance of mid-gap Rashba-like states as exemplified by our theoretical model for decorated TIs. Our experiments show that an interplay of Rashba and Dirac fermions on the surface leads to an intriguing multi-channel weak anti-localization effect concomitant with an unprecedented tuning of the topological protection to transport. Our work offers a new route to engineer topological surface states involving Dirac-Rashba coupling by nano-scale decoration of TI thin films, at the same time shedding light on the real-space mechanism of surface state formation in general.
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Affiliation(s)
- Abhishek Banerjee
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
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35
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Tunable moiré bands and strong correlations in small-twist-angle bilayer graphene. Proc Natl Acad Sci U S A 2017; 114:3364-3369. [PMID: 28292902 DOI: 10.1073/pnas.1620140114] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
According to electronic structure theory, bilayer graphene is expected to have anomalous electronic properties when it has long-period moiré patterns produced by small misalignments between its individual layer honeycomb lattices. We have realized bilayer graphene moiré crystals with accurately controlled twist angles smaller than 1° and studied their properties using scanning probe microscopy and electron transport. We observe conductivity minima at charge neutrality, satellite gaps that appear at anomalous carrier densities for twist angles smaller than 1°, and tunneling densities-of-states that are strongly dependent on carrier density. These features are robust up to large transverse electric fields. In perpendicular magnetic fields, we observe the emergence of a Hofstadter butterfly in the energy spectrum, with fourfold degenerate Landau levels, and broken symmetry quantum Hall states at filling factors ±1, 2, 3. These observations demonstrate that at small twist angles, the electronic properties of bilayer graphene moiré crystals are strongly altered by electron-electron interactions.
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36
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Sanchez-Yamagishi JD, Luo JY, Young AF, Hunt BM, Watanabe K, Taniguchi T, Ashoori RC, Jarillo-Herrero P. Helical edge states and fractional quantum Hall effect in a graphene electron-hole bilayer. NATURE NANOTECHNOLOGY 2017; 12:118-122. [PMID: 27798608 DOI: 10.1038/nnano.2016.214] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 09/13/2016] [Indexed: 05/22/2023]
Abstract
Helical 1D electronic systems are a promising route towards realizing circuits of topological quantum states that exhibit non-Abelian statistics. Here, we demonstrate a versatile platform to realize 1D systems made by combining quantum Hall (QH) edge states of opposite chiralities in a graphene electron-hole bilayer at moderate magnetic fields. Using this approach, we engineer helical 1D edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong non-local transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Unlike other approaches used for realizing helical states, the graphene electron-hole bilayer can be used to build new 1D systems incorporating fractional edge states. Indeed, we are able to tune the bilayer devices into a regime hosting fractional and integer edge states of opposite chiralities, paving the way towards 1D helical conductors with fractional quantum statistics.
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Affiliation(s)
| | - Jason Y Luo
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Andrea F Young
- Department of Physics, University of California Santa Barbara, Santa Barbara, California 93106, USA
| | - Benjamin M Hunt
- Department of Physics, Carnegie Mellon University, Pittsburg, Pennsylvania 15213, USA
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Raymond C Ashoori
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Pablo Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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37
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Broken-Symmetry Quantum Hall States in Twisted Bilayer Graphene. Sci Rep 2016; 6:38068. [PMID: 27905496 PMCID: PMC5131475 DOI: 10.1038/srep38068] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 11/04/2016] [Indexed: 01/29/2023] Open
Abstract
Twisted bilayer graphene offers a unique bilayer two-dimensional-electron system where the layer separation is only in sub-nanometer scale. Unlike Bernal-stacked bilayer, the layer degree of freedom is disentangled from spin and valley, providing eight-fold degeneracy in the low energy states. We have investigated broken-symmetry quantum Hall (QH) states and their transitions due to the interplay of the relative strength of valley, spin and layer polarizations in twisted bilayer graphene. The energy gaps of the broken-symmetry QH states show an electron-hole asymmetric behaviour, and their dependence on the induced displacement field are opposite between even and odd filling factor states. These results strongly suggest that the QH states with broken valley and spin symmetries for individual layer become hybridized via interlayer tunnelling, and the hierarchy of the QH states is sensitive to both magnetic field and displacement field due to charge imbalance between layers.
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38
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Nguyen VL, Perello DJ, Lee S, Nai CT, Shin BG, Kim JG, Park HY, Jeong HY, Zhao J, Vu QA, Lee SH, Loh KP, Jeong SY, Lee YH. Wafer-Scale Single-Crystalline AB-Stacked Bilayer Graphene. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:8177-8183. [PMID: 27414480 DOI: 10.1002/adma.201601760] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Revised: 06/19/2016] [Indexed: 06/06/2023]
Abstract
Single-crystalline artificial AB-stacked bilayer graphene is formed by aligned transfer of two single-crystalline monolayers on a wafer-scale. The obtained bilayer has a well-defined interface and is electronically equivalent to exfoliated or direct-grown AB-stacked bilayers.
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Affiliation(s)
- Van Luan Nguyen
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Physics, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - David J Perello
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Seunghun Lee
- Department of Cogno-mechatronics Engineering, Pusan National University, Busan, 46241, Republic of Korea
| | - Chang Tai Nai
- Department of Chemistry and Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 3 Science Drive 3, Singapore, 117543
| | - Bong Gyu Shin
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Joong-Gyu Kim
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Physics, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Ho Yeol Park
- Department of Cogno-mechatronics Engineering, Pusan National University, Busan, 46241, Republic of Korea
| | - Hu Young Jeong
- UNIST Central Research Facilities, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, Republic of Korea
| | - Jiong Zhao
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Quoc An Vu
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Physics, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Sang Hyub Lee
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Department of Physics, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| | - Kian Ping Loh
- Department of Chemistry and Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 3 Science Drive 3, Singapore, 117543
| | - Se-Young Jeong
- Department of Cogno-mechatronics Engineering, Pusan National University, Busan, 46241, Republic of Korea.
| | - Young Hee Lee
- Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University, Suwon, 16419, Republic of Korea.
- Department of Energy Science, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
- Department of Physics, Sungkyunkwan University, Suwon, 16419, Republic of Korea.
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Cao Y, Luo JY, Fatemi V, Fang S, Sanchez-Yamagishi JD, Watanabe K, Taniguchi T, Kaxiras E, Jarillo-Herrero P. Superlattice-Induced Insulating States and Valley-Protected Orbits in Twisted Bilayer Graphene. PHYSICAL REVIEW LETTERS 2016; 117:116804. [PMID: 27661712 DOI: 10.1103/physrevlett.117.116804] [Citation(s) in RCA: 128] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Indexed: 05/25/2023]
Abstract
Twisted bilayer graphene (TBLG) is one of the simplest van der Waals heterostructures, yet it yields a complex electronic system with intricate interplay between moiré physics and interlayer hybridization effects. We report on electronic transport measurements of high mobility small angle TBLG devices showing clear evidence for insulating states at the superlattice band edges, with thermal activation gaps several times larger than theoretically predicted. Moreover, Shubnikov-de Haas oscillations and tight binding calculations reveal that the band structure consists of two intersecting Fermi contours whose crossing points are effectively unhybridized. We attribute this to exponentially suppressed interlayer hopping amplitudes for momentum transfers larger than the moiré wave vector.
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Affiliation(s)
- Y Cao
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - J Y Luo
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - V Fatemi
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - S Fang
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | | | - K Watanabe
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
| | - E Kaxiras
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - P Jarillo-Herrero
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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40
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Kim Y, Herlinger P, Moon P, Koshino M, Taniguchi T, Watanabe K, Smet JH. Charge Inversion and Topological Phase Transition at a Twist Angle Induced van Hove Singularity of Bilayer Graphene. NANO LETTERS 2016; 16:5053-5059. [PMID: 27387484 DOI: 10.1021/acs.nanolett.6b01906] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
van Hove singularities (VHS's) in the density of states play an outstanding and diverse role for the electronic and thermodynamic properties of crystalline solids. At the critical point the Fermi surface connectivity changes, and topological properties undergo a transition. Opportunities to systematically pass a VHS at the turn of a voltage knob and study its diverse impact are however rare. With the advent of van der Waals heterostructures, control over the atomic registry of neighboring graphene layers offers an unprecedented tool to generate a low energy VHS easily accessible with conventional gating. Here we have addressed magnetotransport when the chemical potential crosses the twist angle induced VHS in twisted bilayer graphene. A topological phase transition is experimentally disclosed in the abrupt conversion of electrons to holes or vice versa, a loss of a nonzero Berry phase and distinct sequences of integer quantum Hall states above and below the singularity.
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Affiliation(s)
- Youngwook Kim
- Max-Planck-Institut für Festköperforschung , 70569 Stuttgart, Germany
| | - Patrick Herlinger
- Max-Planck-Institut für Festköperforschung , 70569 Stuttgart, Germany
| | - Pilkyung Moon
- New York University , Shanghai 200120, China
- NYU-ECNU Institute of Physics at NYU Shanghai , Shanghai 200062, China
| | - Mikito Koshino
- Department of Physics, Tohoku University , Sendai 980-8578, Japan
| | - Takashi Taniguchi
- National Institute for Materials Science , 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science , 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Jurgen H Smet
- Max-Planck-Institut für Festköperforschung , 70569 Stuttgart, Germany
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41
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Chari T, Ribeiro-Palau R, Dean CR, Shepard K. Resistivity of Rotated Graphite-Graphene Contacts. NANO LETTERS 2016; 16:4477-4482. [PMID: 27243333 DOI: 10.1021/acs.nanolett.6b01657] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Robust electrical contact of bulk conductors to two-dimensional (2D) material, such as graphene, is critical to the use of these 2D materials in practical electronic devices. Typical metallic contacts to graphene, whether edge or areal, yield a resistivity of no better than 100 Ω μm but are typically >10 kΩ μm. In this Letter, we employ single-crystal graphite for the bulk contact to graphene instead of conventional metals. The graphite contacts exhibit a transfer length up to four-times longer than in conventional metallic contacts. Furthermore, we are able to drive the contact resistivity to as little as 6.6 Ω μm(2) by tuning the relative orientation of the graphite and graphene crystals. We find that the contact resistivity exhibits a 60° periodicity corresponding to crystal symmetry with additional sharp decreases around 22° and 39°, which are among the commensurate angles of twisted bilayer graphene.
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Affiliation(s)
- Tarun Chari
- Department of Electrical Engineering and ‡Department of Physics, Columbia University , New York, New York 10027, United States
| | - Rebeca Ribeiro-Palau
- Department of Electrical Engineering and ‡Department of Physics, Columbia University , New York, New York 10027, United States
| | - Cory R Dean
- Department of Electrical Engineering and ‡Department of Physics, Columbia University , New York, New York 10027, United States
| | - Kenneth Shepard
- Department of Electrical Engineering and ‡Department of Physics, Columbia University , New York, New York 10027, United States
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42
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Cheng B, Wu Y, Wang P, Pan C, Taniguchi T, Watanabe K, Bockrath M. Gate-Tunable Landau Level Filling and Spectroscopy in Coupled Massive and Massless Electron Systems. PHYSICAL REVIEW LETTERS 2016; 117:026601. [PMID: 27447518 DOI: 10.1103/physrevlett.117.026601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Indexed: 06/06/2023]
Abstract
We report transport studies on coupled massive and massless electron systems, realized using twisted monolayer-graphene-natural bilayer-graphene stacks. We incorporate the layers in a dual-gated transistor geometry enabling independently tuning their charge density and the perpendicular electric field. In a perpendicular magnetic field, we observe a distinct pattern of gate-tunable Landau level crossings. Screening and interlayer electron-electron interactions yield a nonlinear monolayer gate capacitance. Data analysis enables determination of the monolayer's Fermi velocity and the bilayer's effective mass. The mass obtained is larger than that expected for isolated bilayers, suggesting that the interlayer interactions renormalize the band structure.
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Affiliation(s)
- Bin Cheng
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Yong Wu
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Peng Wang
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Cheng Pan
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - T Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - K Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - M Bockrath
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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43
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Abstract
One-atom-thick crystalline layers and their vertical heterostructures carry the promise of designer electronic materials that are unattainable by standard growth techniques. To realize their potential it is necessary to isolate them from environmental disturbances, in particular those introduced by the substrate. However, finding and characterizing suitable substrates, and minimizing the random potential fluctuations they introduce, has been a persistent challenge in this emerging field. Here we show that Landau-level (LL) spectroscopy offers the unique capability to quantify both the reduction of the quasiparticles' lifetime and the long-range inhomogeneity due to random potential fluctuations. Harnessing this technique together with direct scanning tunneling microscopy and numerical simulations we demonstrate that the insertion of a graphene buffer layer with a large twist angle is a very effective method to shield a 2D system from substrate interference that has the additional desirable property of preserving the electronic structure of the system under study. We further show that owing to its remarkable nonlinear screening capability a single graphene buffer layer provides better shielding than either increasing the distance to the substrate or doubling the carrier density and reduces the amplitude of the potential fluctuations in graphene to values even lower than the ones in AB-stacked bilayer graphene.
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44
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Interaction driven quantum Hall effect in artificially stacked graphene bilayers. Sci Rep 2016; 6:24815. [PMID: 27098387 PMCID: PMC4838844 DOI: 10.1038/srep24815] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Accepted: 04/01/2016] [Indexed: 11/16/2022] Open
Abstract
The honeycomb lattice structure of graphene gives rise to its exceptional electronic properties of linear dispersion relation and its chiral nature of charge carriers. The exceptional electronic properties of graphene stem from linear dispersion relation and chiral nature of charge carries, originating from its honeycomb lattice structure. Here, we address the quantum Hall effect in artificially stacked graphene bilayers and single layer graphene grown by chemical vapor deposition. The quantum Hall plateaus started to appear more than 3 T and became clearer at higher magnetic fields up to 9 T. Shubnikov-de Hass oscillations were manifestly observed in graphene bilayers texture. These unusual plateaus may have been due to the layers interaction in artificially stacked graphene bilayers. Our study initiates the understanding of interactions between artificially stacked graphene layers.
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45
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Kim K, Yankowitz M, Fallahazad B, Kang S, Movva HCP, Huang S, Larentis S, Corbet CM, Taniguchi T, Watanabe K, Banerjee SK, LeRoy BJ, Tutuc E. van der Waals Heterostructures with High Accuracy Rotational Alignment. NANO LETTERS 2016; 16:1989-95. [PMID: 26859527 DOI: 10.1021/acs.nanolett.5b05263] [Citation(s) in RCA: 255] [Impact Index Per Article: 31.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment of individual layer crystal axes. We illustrate the approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers of monolayer graphene flakes. The Raman spectra of this artificial bilayer graphene possess a wide 2D band, which is best fit by four Lorentzians, consistent with Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on the artificial bilayer graphene, and tunneling spectroscopy as a function of gate voltage reveals a constant density of states, also in agreement with Bernal stacking. In addition, electron transport probed in dual-gated samples reveals a band gap opening as a function of transverse electric field. To illustrate the applicability of this technique to realize vdW heterostructuctures in which the functionality is critically dependent on rotational alignment, we demonstrate resonant tunneling double bilayer graphene heterostructures separated by hexagonal boron-nitride dielectric.
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Affiliation(s)
- Kyounghwan Kim
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Matthew Yankowitz
- Physics Department, University of Arizona , Tucson, Arizona 85721, United States
| | - Babak Fallahazad
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Sangwoo Kang
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Hema C P Movva
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Shengqiang Huang
- Physics Department, University of Arizona , Tucson, Arizona 85721, United States
| | - Stefano Larentis
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Chris M Corbet
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Takashi Taniguchi
- National Institute for Materials Science, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan
| | - Sanjay K Banerjee
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
| | - Brian J LeRoy
- Physics Department, University of Arizona , Tucson, Arizona 85721, United States
| | - Emanuel Tutuc
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States
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46
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Yabuki N, Moriya R, Arai M, Sata Y, Morikawa S, Masubuchi S, Machida T. Supercurrent in van der Waals Josephson junction. Nat Commun 2016; 7:10616. [PMID: 26830754 PMCID: PMC4740878 DOI: 10.1038/ncomms10616] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 01/05/2016] [Indexed: 11/09/2022] Open
Abstract
Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency. Van der Waals heterostructures, made of stacked two-dimensional materials, hold promise for modern electronics. Here, the authors build van der Waals junction between superconducting two-dimensional materials and reveal that the junction works as Josephson junction.
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Affiliation(s)
- Naoto Yabuki
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Rai Moriya
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Miho Arai
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Yohta Sata
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Sei Morikawa
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Satoru Masubuchi
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
| | - Tomoki Machida
- Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan.,Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
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47
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Lee Y, Tran D, Myhro K, Velasco J, Gillgren N, Poumirol JM, Smirnov D, Barlas Y, Lau CN. Multicomponent Quantum Hall Ferromagnetism and Landau Level Crossing in Rhombohedral Trilayer Graphene. NANO LETTERS 2016; 16:227-231. [PMID: 26636471 DOI: 10.1021/acs.nanolett.5b03574] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Using transport measurements, we investigate multicomponent quantum Hall (QH) ferromagnetism in dual-gated rhombohedral trilayer graphene (r-TLG) in which the real spin, orbital pseudospin, and layer pseudospins of the lowest Landau level form spontaneous ordering. We observe intermediate QH plateaus, indicating a complete lifting of the degeneracy of the zeroth Landau level (LL) in the hole-doped regime. In charge neutral r-TLG, the orbital degeneracy is broken first, and the layer degeneracy is broken last and only in the presence of an interlayer potential U⊥. In the phase space of U⊥ and filling factor ν, we observe an intriguing "hexagon" pattern, which is accounted for by a model based on crossings between symmetry-broken LLs.
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Affiliation(s)
- Y Lee
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
| | - D Tran
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
| | - K Myhro
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
| | - J Velasco
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
| | - N Gillgren
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
| | - J M Poumirol
- National High Magnetic Field Laboratory , Tallahassee, Florida 32310, United States
| | - D Smirnov
- National High Magnetic Field Laboratory , Tallahassee, Florida 32310, United States
| | - Y Barlas
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
| | - C N Lau
- Department of Physics and Astronomy, University of California, Riverside , Riverside, California 91765, United States
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48
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Abstract
We outline a designer approach to endow widely available plain materials with topological properties by stacking them atop other nontopological materials. The approach is illustrated with a model system comprising graphene stacked atop hexagonal boron nitride. In this case, the Berry curvature of the electron Bloch bands is highly sensitive to the stacking configuration. As a result, electron topology can be controlled by crystal axes alignment, granting a practical route to designer topological materials. Berry curvature manifests itself in transport via the valley Hall effect and long-range chargeless valley currents. The nonlocal electrical response mediated by such currents provides diagnostics for band topology.
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Chung TF, He R, Wu TL, Chen YP. Optical phonons in twisted bilayer graphene with gate-induced asymmetric doping. NANO LETTERS 2015; 15:1203-1210. [PMID: 25621859 DOI: 10.1021/nl504318a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Twisted bilayer graphene (tBLG) devices with ion gel gate dielectrics are studied using Raman spectroscopy in the twist angle regime where a resonantly enhanced G band can be observed. We observe prominent splitting and intensity quenching on the G Raman band when the carrier density is tuned away from charge neutrality. This G peak splitting is attributed to asymmetric charge doping in the two graphene layers, which reveals individual phonon self-energy renormalization of the two weakly coupled layers of graphene. We estimate the effective interlayer capacitance at low doping density of tBLG using an interlayer screening model. The anomalous intensity quenching of both G peaks is ascribed to the suppression of resonant interband transitions between the two saddle points (van Hove singularities) that are displaced in the momentum space by gate-tuning. In addition, we observe a softening (hardening) of the R Raman band, a superlattice-induced phonon mode in tBLG, in electron (hole) doping. Our results demonstrate that gate modulation can be used to control the optoelectronic and vibrational properties in tBLG devices.
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Affiliation(s)
- Ting-Fung Chung
- Department of Physics and Astronomy and ‡Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States
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Probing the electron states and metal-insulator transition mechanisms in molybdenum disulphide vertical heterostructures. Nat Commun 2015; 6:6088. [PMID: 25586302 DOI: 10.1038/ncomms7088] [Citation(s) in RCA: 154] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2014] [Accepted: 12/11/2014] [Indexed: 12/23/2022] Open
Abstract
The metal-insulator transition is one of the remarkable electrical properties of atomically thin molybdenum disulphide. Although the theory of electron-electron interactions has been used in modelling the metal-insulator transition in molybdenum disulphide, the underlying mechanism and detailed transition process still remain largely unexplored. Here we demonstrate that the vertical metal-insulator-semiconductor heterostructures built from atomically thin molybdenum disulphide are ideal capacitor structures for probing the electron states. The vertical configuration offers the added advantage of eliminating the influence of large impedance at the band tails and allows the observation of fully excited electron states near the surface of molybdenum disulphide over a wide excitation frequency and temperature range. By combining capacitance and transport measurements, we have observed a percolation-type metal-insulator transition, driven by density inhomogeneities of electron states, in monolayer and multilayer molybdenum disulphide. In addition, the valence band of thin molybdenum disulphide layers and their intrinsic properties are accessed.
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