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Lu Q, Le C, Zhang X, Cook J, He X, Zarenia M, Vaninger M, Miceli PF, Singh DJ, Liu C, Qin H, Chiang TC, Chiu CK, Vignale G, Bian G. Dirac Fermion Cloning, Moiré Flat Bands, and Magic Lattice Constants in Epitaxial Monolayer Graphene. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2200625. [PMID: 35446987 DOI: 10.1002/adma.202200625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 04/14/2022] [Indexed: 06/14/2023]
Abstract
Tuning interactions between Dirac states in graphene has attracted enormous interest because it can modify the electronic spectrum of the 2D material, enhance electron correlations, and give rise to novel condensed-matter phases such as superconductors, Mott insulators, Wigner crystals, and quantum anomalous Hall insulators. Previous works predominantly focus on the flat band dispersion of coupled Dirac states from different twisted graphene layers. In this work, a new route to realizing flat band physics in monolayer graphene under a periodic modulation from substrates is proposed. Graphene/SiC heterostructure is taken as a prototypical example and it is demonstrated experimentally that the substrate modulation leads to Dirac fermion cloning and, consequently, the proximity of the two Dirac cones of monolayer graphene in momentum space. Theoretical modeling captures the cloning mechanism of the Dirac states and indicates that moiré flat bands can emerge at certain magic lattice constants of the substrate, specifically when the period of modulation becomes nearly commensurate with the ( 3 × 3 ) R 30 o \[(\sqrt 3 \; \times \;\sqrt 3 )R{30^o}\] supercell of graphene. The results show that epitaxial single monolayer graphene on suitable substrates is a promising platform for exploring exotic many-body quantum phases arising from interactions between Dirac electrons.
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Affiliation(s)
- Qiangsheng Lu
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Congcong Le
- RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Wako, Saitama, 351-0198, Japan
| | - Xiaoqian Zhang
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Jacob Cook
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Xiaoqing He
- Electron Microscopy Core Facility, University of Missouri, Columbia, MO, 65211, USA
- Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO, 65211, USA
| | - Mohammad Zarenia
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Mitchel Vaninger
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Paul F Miceli
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - David J Singh
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Chang Liu
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Hailang Qin
- Department of Physics, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Tai-Chang Chiang
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL, 61801-3080, USA
- Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, IL, 61801-2902, USA
| | - Ching-Kai Chiu
- RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Wako, Saitama, 351-0198, Japan
| | - Giovanni Vignale
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
| | - Guang Bian
- Department of Physics and Astronomy, University of Missouri, Columbia, MO, 65211, USA
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Ienaga K, Iimori T, Yaji K, Miyamachi T, Nakashima S, Takahashi Y, Fukuma K, Hayashi S, Kajiwara T, Visikovskiy A, Mase K, Nakatsuji K, Tanaka S, Komori F. Modulation of Electron-Phonon Coupling in One-Dimensionally Nanorippled Graphene on a Macrofacet of 6H-SiC. NANO LETTERS 2017; 17:3527-3532. [PMID: 28520435 DOI: 10.1021/acs.nanolett.7b00606] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Local electron-phonon coupling of a one-dimensionally nanorippled graphene is studied on a SiC(0001) vicinal substrate. We have characterized local atomic and electronic structures of a periodically nanorippled graphene (3.4 nm period) prepared on a macrofacet of the 6H-SiC crystal using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES). The rippled graphene on the macrofacets distributes homogeneously over the 6H-SiC substrate in a millimeter scale, and thus replica bands are detected by the macroscopic ARPES. The STM/STS results indicate the strength of electron-phonon coupling to the out-of-plane phonon at the K̅ points of graphene is periodically modified in accordance with the ripple structure. We propose an interface carbon nanostructure with graphene nanoribbons between the surface rippled graphene and the substrate SiC that periodically modifies the electron-phonon coupling in the surface graphene.
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Affiliation(s)
- Koichiro Ienaga
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Takushi Iimori
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Koichiro Yaji
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Toshio Miyamachi
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Shuhei Nakashima
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Yukio Takahashi
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
| | - Kohei Fukuma
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Shingo Hayashi
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Takashi Kajiwara
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Anton Visikovskiy
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Kazuhiko Mase
- Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK) , Tsukuba 305-0801, Japan
- Department of Materials Structure Science, SOKENDAI (The Graduate University for Advanced Studies) , 1-1 Oho, Tsukuba 305-0801, Japan
| | - Kan Nakatsuji
- Department of Materials Science and Engineering, Tokyo Institute of Technology , Yokohama 226-8502, Japan
| | - Satoru Tanaka
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University , Fukuoka 819-0395, Japan
| | - Fumio Komori
- Institute for Solid State Physics, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
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Hiraoka N, Nomura T. Electron momentum densities near Dirac cones: Anisotropic Umklapp scattering and momentum broadening. Sci Rep 2017; 7:565. [PMID: 28373659 PMCID: PMC5428786 DOI: 10.1038/s41598-017-00628-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2016] [Accepted: 03/08/2017] [Indexed: 11/09/2022] Open
Abstract
The relationship between electron momentum densities (EMDs) and a band gap is clarified in momentum space. The interference between wavefunctions via reciprocal lattice vectors, making a band gap in momentum space, causes the scattering of electrons from the first Brillouin zone to the other zones, so-called Umklapp scattering. This leads to the broadening of EMDs. A sharp drop of the EMD in the limit of a zero gap becomes broadened as the gap opens. The broadening is given by a simple quantity, Eg/vF, where Eg is the gap magnitude and vF the Fermi velocity. As the ideal case to see such an effect, we investigate the EMDs in graphene and graphite. They are basically semimetals, and their EMDs have a hexagonal shape enclosed in the first Brillouin zone. Since the gap is zero at Dirac points, a sharp drop exists at the corners (K/K’ points) while the broadening becomes significant away from K/K’s, showing the smoothest fall at the centers of the edges (M’s). In fact, this unique topology mimics a general variation of the EMDs across the metal-insulator transition in condensed matters. Such an anisotropic broadening effect is indeed observed by momentum-density-based experiments e.g. x-ray Compton scattering.
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Affiliation(s)
- N Hiraoka
- National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu, 30076, Taiwan.
| | - T Nomura
- National Institutes for Quantum and Radiological Science and Technology (QST), SPring-8, 1-1-1 Kouto, Sayo, Hyogo, 679-5148, Japan
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Tanaka SI, Matsunami M, Kimura SI. An investigation of electron-phonon coupling via phonon dispersion measurements in graphite using angle-resolved photoelectron spectroscopy. Sci Rep 2013; 3:3031. [PMID: 24149916 PMCID: PMC3805971 DOI: 10.1038/srep03031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2013] [Accepted: 10/08/2013] [Indexed: 11/23/2022] Open
Abstract
Electron-phonon coupling (EPC) plays an important role in solid state physics. Here, we demonstrate an experimental method that enables investigation of the elemental processes of the indirect transition, in which EPC participates in photoexcitation in solids, by resolving the energy and momentum of phonons and electrons simultaneously. For graphite, we used angle-resolved photoelectron spectroscopy to observe electron emission at the Γ-point being scattered from the K-point by a phonon. Energy conservation during phonon emission implies that the step-like structure in the spectrum is near the Fermi level, and angle-resolved measurements revealed phonon dispersions that contribute to EPC because of parallel momentum conservation. The observed phonon branch depends on the photon energy, i.e., the final photoexcitation state; this dependency is partly explained by the selection rule, which is determined by the electron state symmetry for the initial, intermediate, and final states and the phonon.
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Affiliation(s)
- Shin-ichiro Tanaka
- The Institute of Industrial and Scientific Research, Osaka University, 567-0047 Mihogaoka, Ibaraki, Osaka, Japan
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Kondo T, Nakashima Y, Ota Y, Ishida Y, Malaeb W, Okazaki K, Shin S, Kriener M, Sasaki S, Segawa K, Ando Y. Anomalous dressing of Dirac fermions in the topological surface state of Bi2Se3, Bi2Te3, and Cu-doped Bi2Se3. PHYSICAL REVIEW LETTERS 2013; 110:217601. [PMID: 23745936 DOI: 10.1103/physrevlett.110.217601] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Indexed: 06/02/2023]
Abstract
Quasiparticle dynamics on the topological surface state of Bi(2(3), Bi(2)Te(3), and superconducting Cu(x)Bi(2)Se(3) are studied by 7 eV laser-based angle resolved photoemission spectroscopy. We find strong mode couplings in the Dirac-cone surface states at energies of ~3 and ~15-20 meV associated with an exceptionally large coupling constant λ of ~3, which is one of the strongest ever reported for any material. This result is compatible with the recent observation of a strong Kohn anomaly in the surface phonon dispersion of Bi(2)Se(3), but it appears that the theoretically proposed "spin-plasmon" excitations realized in helical metals are also playing an important role. Intriguingly, the ~3 meV mode coupling is found to be enhanced in the superconducting state of Cu(x)Bi(2)Se(3).
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Affiliation(s)
- Takeshi Kondo
- ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
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Liu Y, Bian G, Miller T, Chiang TC. Visualizing electronic chirality and Berry phases in graphene systems using photoemission with circularly polarized light. PHYSICAL REVIEW LETTERS 2011; 107:166803. [PMID: 22107416 DOI: 10.1103/physrevlett.107.166803] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2011] [Indexed: 05/31/2023]
Abstract
Electronic chirality near the Dirac point is a key property of graphene systems, which is revealed by the spectral intensity patterns as measured by angle-resolved photoemission spectroscopy under various polarization conditions. Specifically, the strongly modulated circular patterns for monolayer (bilayer) graphene rotate by ±90° (±45°) in changing from linearly to circularly polarized light; these angles are directly related to the phases of the wave functions and thus visually confirm the Berry's phase of π (2π) around the Dirac point. The details are verified by calculations.
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Affiliation(s)
- Y Liu
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3080, USA
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Ishida Y, Togashi T, Yamamoto K, Tanaka M, Taniuchi T, Kiss T, Nakajima M, Suemoto T, Shin S. Non-thermal hot electrons ultrafastly generating hot optical phonons in graphite. Sci Rep 2011; 1:64. [PMID: 22355583 PMCID: PMC3216551 DOI: 10.1038/srep00064] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Accepted: 07/25/2011] [Indexed: 11/28/2022] Open
Abstract
Investigation of the non-equilibrium dynamics after an impulsive impact provides insights into couplings among various excitations. A two-temperature model (TTM) is often a starting point to understand the coupled dynamics of electrons and lattice vibrations: the optical pulse primarily raises the electronic temperature T(el) while leaving the lattice temperature T(l) low; subsequently the hot electrons heat up the lattice until T(el) = T(l) is reached. This temporal hierarchy owes to the assumption that the electron-electron scattering rate is much larger than the electron-phonon scattering rate. We report herein that the TTM scheme is seriously invalidated in semimetal graphite. Time-resolved photoemission spectroscopy (TrPES) of graphite reveals that fingerprints of coupled optical phonons (COPs) occur from the initial moments where T(el) is still not definable. Our study shows that ultrafast-and-efficient phonon generations occur beyond the TTM scheme, presumably associated to the long duration of the non-thermal electrons in graphite.
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Affiliation(s)
- Y Ishida
- ISSP, University of Tokyo, Kashiwa-no-ha, Kashiwa, Chiba 277-8581, Japan.
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