1
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Mella JD, Calvo HL, Foa Torres LEF. Entangled States Induced by Electron-Phonon Interaction in Two-Dimensional Materials. NANO LETTERS 2023. [PMID: 37984421 DOI: 10.1021/acs.nanolett.3c03316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
We report on the effects of electron-phonon interaction in materials such as graphene, showing that it enables the formation of a gap bridged by unique edge states. These states exhibit a distinctive locking among propagation direction, valley, and phonon mode, allowing for the generation of electron-phonon entangled states whose parts can be easily split. We discuss the effect of the chiral atomic motion in the zone boundary phonons leading to this effect. Our findings shed light on how to harness these unconventional states in quantum research.
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Affiliation(s)
- José D Mella
- Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 8370448 Santiago, Chile
- School of Engineering and Sciences, Universidad Adolfo Ibáñez, 7941169 Santiago, Chile
| | - Hernán L Calvo
- Instituto de Física Enrique Gaviola (CONICET) and FaMAF, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina
| | - Luis E F Foa Torres
- Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 8370448 Santiago, Chile
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2
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Li Y, Wan Q, Xu N. Recent Advances in Moiré Superlattice Systems by Angle-Resolved Photoemission Spectroscopy. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023:e2305175. [PMID: 37689836 DOI: 10.1002/adma.202305175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 08/16/2023] [Indexed: 09/11/2023]
Abstract
The last decade has witnessed a flourish in 2D materials including graphene and transition metal dichalcogenides (TMDs) as atomic-scale Legos. Artificial moiré superlattices via stacking 2D materials with a twist angle and/or a lattice mismatch have recently become a fertile playground exhibiting a plethora of emergent properties beyond their building blocks. These rich quantum phenomena stem from their nontrivial electronic structures that are effectively tuned by the moiré periodicity. Modern angle-resolved photoemission spectroscopy (ARPES) can directly visualize electronic structures with decent momentum, energy, and spatial resolution, thus can provide enlightening insights into fundamental physics in moiré superlattice systems and guides for designing novel devices. In this review, first, a brief introduction is given on advanced ARPES techniques and basic ideas of band structures in a moiré superlattice system. Then ARPES research results of various moiré superlattice systems are highlighted, including graphene on substrates with small lattice mismatches, twisted graphene/TMD moiré systems, and high-order moiré superlattice systems. Finally, it discusses important questions that remain open, challenges in current experimental investigations, and presents an outlook on this field of research.
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Affiliation(s)
- Yiwei Li
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
| | - Qiang Wan
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
| | - Nan Xu
- Institute for Advanced Studies (IAS), Wuhan University, Wuhan, 430072, China
- Wuhan Institute of Quantum Technology, Wuhan, 430206, China
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3
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Grubišić-Čabo A, Michiardi M, Sanders CE, Bianchi M, Curcio D, Phuyal D, Berntsen MH, Guo Q, Dendzik M. In Situ Exfoliation Method of Large-Area 2D Materials. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023:e2301243. [PMID: 37236159 PMCID: PMC10401183 DOI: 10.1002/advs.202301243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Indexed: 05/28/2023]
Abstract
2D materials provide a rich platform to study novel physical phenomena arising from quantum confinement of charge carriers. Many of these phenomena are discovered by surface sensitive techniques, such as photoemission spectroscopy, that work in ultra-high vacuum (UHV). Success in experimental studies of 2D materials, however, inherently relies on producing adsorbate-free, large-area, high-quality samples. The method that yields 2D materials of highest quality is mechanical exfoliation from bulk-grown samples. However, as this technique is traditionally performed in a dedicated environment, the transfer of samples into vacuum requires surface cleaning that might diminish the quality of the samples. In this article, a simple method for in situ exfoliation directly in UHV is reported, which yields large-area, single-layered films. Multiple metallic and semiconducting transition metal dichalcogenides are exfoliated in situ onto Au, Ag, and Ge. The exfoliated flakes are found to be of sub-millimeter size with excellent crystallinity and purity, as supported by angle-resolved photoemission spectroscopy, atomic force microscopy, and low-energy electron diffraction. The approach is well-suited for air-sensitive 2D materials, enabling the study of a new suite of electronic properties. In addition, the exfoliation of surface alloys and the possibility of controlling the substrate-2D material twist angle is demonstrated.
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Affiliation(s)
- Antonija Grubišić-Čabo
- Zernike Institute for Advanced Materials, University of Groningen, Groningen, 9747 AG, The Netherlands
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, Stockholm, 114 19, Sweden
| | - Matteo Michiardi
- Quantum Matter Institute, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
| | - Charlotte E Sanders
- Central Laser Facility, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Campus, Didcot, 0X11 0QX, UK
| | - Marco Bianchi
- School of Physics and Astronomy, Aarhus University, Aarhus, 8000 C, Denmark
| | - Davide Curcio
- School of Physics and Astronomy, Aarhus University, Aarhus, 8000 C, Denmark
| | - Dibya Phuyal
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, Stockholm, 114 19, Sweden
| | - Magnus H Berntsen
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, Stockholm, 114 19, Sweden
| | - Qinda Guo
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, Stockholm, 114 19, Sweden
| | - Maciej Dendzik
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, Stockholm, 114 19, Sweden
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4
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Liu Q, Lu X, Liu Y, Li Z, Yan P, Chen W, Meng Q, Zhang Y, Yam C, He L, Yan Y, Zhang Y, Wu J, Frauenheim T, Zhang R, Xu Y. Carrier Relaxation and Multiplication in Bi Doped Graphene. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 19:e2206218. [PMID: 36670078 DOI: 10.1002/smll.202206218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 01/09/2023] [Indexed: 05/04/2023]
Abstract
By introducing different contents of Bi adatoms to the surface of monolayer graphene, the carrier concentration and their dynamics have been effectively modulated as probed directly by the time- and angle-resolved photoemission spectroscopy technique. The Bi adatoms are found to assist acoustic phonon scattering events mediated by supercollisions as the disorder effectively relaxes the momentum conservation constraint. A reduced carrier multiplication has been observed, which is related to the shrinking Fermi sea for scattering, as confirmed by time-dependent density functional theory simulation. This work gives insight into hot carrier dynamics in graphene, which is crucial for promoting the application of photoelectric devices.
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Affiliation(s)
- Qi Liu
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Xianyang Lu
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Yuxiang Liu
- Bremen Center for Computational Materials Science, University of Bremen, Am Fallturm 1, 28359, Bremen, Germany
| | - Zhihao Li
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Pengfei Yan
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Wang Chen
- National Laboratory of Solid State Microstructure, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Qinghao Meng
- National Laboratory of Solid State Microstructure, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Yongheng Zhang
- National Laboratory of Solid State Microstructure, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - ChiYung Yam
- Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Shenzhen, 518000, China
- Hong Kong Quantum AI Lab Limited, Hong Kong, 00000, China
| | - Liang He
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Yu Yan
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Yi Zhang
- National Laboratory of Solid State Microstructure, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, China
| | - Jing Wu
- York-Nanjing Joint Center (YNJC) for Spintronics and Nano-engineering, Department of Electronics and Physics, University of York, York, YO10 5DD, UK
| | - Thomas Frauenheim
- Bremen Center for Computational Materials Science, University of Bremen, Am Fallturm 1, 28359, Bremen, Germany
- Beijing Computational Science Research Center, Haidian District, Beijing, 100193, China
- Shenzhen JL Computational Science and Applied Research Institute, Shenzhen, 518109, China
| | - Rong Zhang
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
| | - Yongbing Xu
- Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing, 210093, China
- York-Nanjing Joint Center (YNJC) for Spintronics and Nano-engineering, Department of Electronics and Physics, University of York, York, YO10 5DD, UK
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5
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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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6
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Rich nature of Van Hove singularities in Kagome superconductor CsV 3Sb 5. Nat Commun 2022; 13:2220. [PMID: 35468883 PMCID: PMC9038924 DOI: 10.1038/s41467-022-29828-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Accepted: 03/30/2022] [Indexed: 11/16/2022] Open
Abstract
The recently discovered layered kagome metals AV3Sb5 (A = K, Rb, Cs) exhibit diverse correlated phenomena, which are intertwined with a topological electronic structure with multiple van Hove singularities (VHSs) in the vicinity of the Fermi level. As the VHSs with their large density of states enhance correlation effects, it is of crucial importance to determine their nature and properties. Here, we combine polarization-dependent angle-resolved photoemission spectroscopy with density functional theory to directly reveal the sublattice properties of 3d-orbital VHSs in CsV3Sb5. Four VHSs are identified around the M point and three of them are close to the Fermi level, with two having sublattice-pure and one sublattice-mixed nature. Remarkably, the VHS just below the Fermi level displays an extremely flat dispersion along MK, establishing the experimental discovery of higher-order VHS. The characteristic intensity modulation of Dirac cones around K further demonstrates the sublattice interference embedded in the kagome Fermiology. The crucial insights into the electronic structure, revealed by our work, provide a solid starting point for the understanding of the intriguing correlation phenomena in the kagome metals AV3Sb5. Predictions suggest enhanced correlation effect due to multiple van Hove singularities (VHS) in the vicinity of the Fermi level in the recently discovered AV3Sb5 kagome metals. Here the authors identify three VHSs close to the Fermi level with diverse sublattice characters in CsV3Sb5, and one of them shows flat dispersion suggesting the higher-order nature.
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7
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Hamer M, Giampietri A, Kandyba V, Genuzio F, Menteş TO, Locatelli A, Gorbachev RV, Barinov A, Mucha-Kruczyński M. Moiré Superlattice Effects and Band Structure Evolution in Near-30-Degree Twisted Bilayer Graphene. ACS NANO 2022; 16:1954-1962. [PMID: 35073479 PMCID: PMC9007532 DOI: 10.1021/acsnano.1c06439] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Accepted: 01/20/2022] [Indexed: 06/01/2023]
Abstract
In stacks of two-dimensional crystals, mismatch of their lattice constants and misalignment of crystallographic axes lead to formation of moiré patterns. We show that moiré superlattice effects persist in twisted bilayer graphene (tBLG) with large twists and short moiré periods. Using angle-resolved photoemission, we observe dramatic changes in valence band topology across large regions of the Brillouin zone, including the vicinity of the saddle point at M and across 3 eV from the Dirac points. In this energy range, we resolve several moiré minibands and detect signatures of secondary Dirac points in the reconstructed dispersions. For twists θ > 21.8°, the low-energy minigaps are not due to cone anticrossing as is the case at smaller twist angles but rather due to moiré scattering of electrons in one graphene layer on the potential of the other which generates intervalley coupling. Our work demonstrates the robustness of the mechanisms which enable engineering of electronic dispersions of stacks of two-dimensional crystals by tuning the interface twist angles. It also shows that large-angle tBLG hosts electronic minigaps and van Hove singularities of different origin which, given recent progress in extreme doping of graphene, could be explored experimentally.
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Affiliation(s)
- Matthew
J. Hamer
- Department
of Physics, University of Manchester, Oxford Road, Manchester M13 9PL, United
Kingdom
- National
Graphene Institute, University of Manchester, Booth Street East, Manchester M13 9PL, United Kingdom
| | | | | | | | | | | | - Roman V. Gorbachev
- Department
of Physics, University of Manchester, Oxford Road, Manchester M13 9PL, United
Kingdom
- National
Graphene Institute, University of Manchester, Booth Street East, Manchester M13 9PL, United Kingdom
- Henry
Royce Institute, Oxford
Road, Manchester M13 9PL, United Kingdom
| | | | - Marcin Mucha-Kruczyński
- Department
of Physics, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
- Centre
for Nanoscience and Nanotechnology, University
of Bath, Claverton Down, Bath BA2
7AY, United Kingdom
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8
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Wen F, Zhang S, Hui S, Ma H, Wang S, Ye H, Wang W, Zhu T, Zhang Y, Wang H. Terahertz tunable optically induced lattice in the magnetized monolayer graphene. OPTICS EXPRESS 2022; 30:2852-2862. [PMID: 35209417 DOI: 10.1364/oe.448926] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 12/31/2021] [Indexed: 06/14/2023]
Abstract
The emergence of monolayer material has opened new avenue for manipulating light beyond the capability of traditional optics. However, controlling the terahertz (THz) wave with magnetized monolayer graphene based on multi-beam interference method is interesting but yet reported. In this article, we report an optically induced lattice with tunability in THz by interfering four plane waves in the magnetized monolayer graphene. We show that the optical properties of the induced optical lattice can be efficiently tuned by varying the optical parameter of the interference beams (i.e., the photon detuning and the Rabi frequency), resulting in both amplitude- and phase-type lattice. Based on Fraunhofer diffraction theory, it is found that the far-field diffraction efficiency is adjustable via varying the probe detuning. Moreover, it is also found that the probe field is diffracted into the high-order direction when the photon detuning is within the triangle-like anti-centrosymmetric region. Such a tunable THz lattice may provide a versatile tool for all-optical switching at the few photons level and paves the way for next generation high-speed wireless communication.
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9
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Wang C, Wang H, Chen W, Xie X, Zong J, Liu L, Jin S, Zhang Y, Yu F, Meng Q, Tian Q, Wang L, Ren W, Li F, Zhang H, Zhang Y. Direct Observation of Global Elastic Intervalley Scattering Induced by Impurities on Graphene. NANO LETTERS 2021; 21:8258-8265. [PMID: 34570496 DOI: 10.1021/acs.nanolett.1c02714] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The scattering process induced by impurities in graphene plays a key role in transport properties. Especially, the disorder impurities can drive the ordered state with a hexagonal superlattice on graphene by electron-mediated interaction at a transition temperature. Using angle-resolved photoemission spectroscopy (ARPES), we reveal that the epitaxial monolayer and bilayer graphene with various impurities display global elastic intervalley scattering and quantum interference below the critical temperature (34 K), which leads to a set of new folded Dirac cones at the Brillouin-zone center by mixing two inequivalent Dirac cones. The Dirac electrons generated from intervalley scattering without chirality can be due to the breaking of the sublattice symmetry. In addition, the temperature-dependent ARPES measurements indicate the thermal damping of quantum interference patterns from Dirac electron scattering on impurities. Our results demonstrate that the electron scattering and interference induced by impurities can completely modulate the Dirac bands of graphene.
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Affiliation(s)
- Can Wang
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Huaiqiang Wang
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Wang Chen
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Xuedong Xie
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Junyu Zong
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Lulu Liu
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Shaoen Jin
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Yongheng Zhang
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Fan Yu
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Qinghao Meng
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Qichao Tian
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
| | - Li Wang
- Vacuum Interconnected Nanotech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences (CAS), Suzhou 215123, China
| | - Wei Ren
- Vacuum Interconnected Nanotech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences (CAS), Suzhou 215123, China
| | - Fangsen Li
- Vacuum Interconnected Nanotech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics (SINANO), Chinese Academy of Sciences (CAS), Suzhou 215123, China
| | - Haijun Zhang
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yi Zhang
- National Laboratory of Solid State Microstructure, School of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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10
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Anwar F, Iurov A, Huang D, Gumbs G, Sharma A. Coherent-scatterer enhancement and Klein-tunneling suppression by potential barriers in gapped graphene with chirality-time-reversal symmetry. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:505701. [PMID: 34544062 DOI: 10.1088/1361-648x/ac2866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Accepted: 09/20/2021] [Indexed: 06/13/2023]
Abstract
We have utilized the finite-difference approach to explore electron-tunneling properties in gapped graphene through various electrostatic-potential barriers ranging from Gaussian to a triangular envelope function in comparison with a square potential barrier. The transmission coefficient is calculated numerically for each case and applied to the corresponding tunneling conductance. It is well known that Klein tunneling in graphene will be greatly reduced in gapped graphene. Our results further demonstrate that such a decrease of transmission can be significantly enhanced for spatially-modulated potential barriers. Moreover, we investigate the effect from a bias field applied to those barrier profiles, from which we show that it enables the control of electron flow under normal incidence. Meanwhile, the suppression of Klein tunneling is found more severe for a non-square barrier and exhibits a strong dependence on bias-field polarity for all kinds of barriers. Finally, roles of a point impurity on electron transmission and conductance are analyzed with a sharp peak appearing in electron conductance as the impurity atom is placed in the middle of a square barrier. For narrow triangular and Gaussian barriers, however, the conductance peaks become significantly broadened, associated with an enhancement in tunneling conductance.
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Affiliation(s)
- Farhana Anwar
- Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720, United states of America
| | - Andrii Iurov
- Department of Physics and Computer Science, Medgar Evers College of the City University of New York, Brooklyn, NY 11225, United States of America
| | - Danhong Huang
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, NM 87117, 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
| | - Ashwani Sharma
- Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, NM 87117, United States of America
- Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, NM 87106, United States of America
- Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87106, United States of America
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11
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Chernenko K, Kivimäki A, Pärna R, Wang W, Sankari R, Leandersson M, Tarawneh H, Pankratov V, Kook M, Kukk E, Reisberg L, Urpelainen S, Käämbre T, Siewert F, Gwalt G, Sokolov A, Lemke S, Alimov S, Knedel J, Kutz O, Seliger T, Valden M, Hirsimäki M, Kirm M, Huttula M. Performance and characterization of the FinEstBeAMS beamline at the MAX IV Laboratory. JOURNAL OF SYNCHROTRON RADIATION 2021; 28:1620-1630. [PMID: 34475309 PMCID: PMC8415336 DOI: 10.1107/s1600577521006032] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 06/09/2021] [Indexed: 05/14/2023]
Abstract
FinEstBeAMS (Finnish-Estonian Beamline for Atmospheric and Materials Sciences) is a multidisciplinary beamline constructed at the 1.5 GeV storage ring of the MAX IV synchrotron facility in Lund, Sweden. The beamline covers an extremely wide photon energy range, 4.5-1300 eV, by utilizing a single elliptically polarizing undulator as a radiation source and a single grazing-incidence plane grating monochromator to disperse the radiation. At photon energies below 70 eV the beamline operation relies on the use of optical and thin-film filters to remove higher-order components from the monochromated radiation. This paper discusses the performance of the beamline, examining such characteristics as the quality of the gratings, photon energy calibration, photon energy resolution, available photon flux, polarization quality and focal spot size.
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Affiliation(s)
- Kirill Chernenko
- MAX IV Laboratory, Lund University, PO Box 118, SE-22100 Lund, Sweden
- Correspondence e-mail:
| | - Antti Kivimäki
- MAX IV Laboratory, Lund University, PO Box 118, SE-22100 Lund, Sweden
- Nano and Molecular Systems Research Unit, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland
| | - Rainer Pärna
- Institute of Physics, University of Tartu, W. Ostwald Street 1, EE-51014 Tartu, Estonia
| | - Weimin Wang
- MAX IV Laboratory, Lund University, PO Box 118, SE-22100 Lund, Sweden
| | - Rami Sankari
- Computational Physics Laboratory, Tampere University, PO Box 692, FI-33014 Tampere, Finland
| | - Mats Leandersson
- MAX IV Laboratory, Lund University, PO Box 118, SE-22100 Lund, Sweden
| | - Hamed Tarawneh
- MAX IV Laboratory, Lund University, PO Box 118, SE-22100 Lund, Sweden
| | - Vladimir Pankratov
- Institute of Solid State Physics, University of Latvia, 8 Kengaraga iela, LV-1063 Riga, Latvia
| | - Mati Kook
- Institute of Physics, University of Tartu, W. Ostwald Street 1, EE-51014 Tartu, Estonia
| | - Edwin Kukk
- Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
| | - Liis Reisberg
- Institute of Physics, University of Tartu, W. Ostwald Street 1, EE-51014 Tartu, Estonia
| | - Samuli Urpelainen
- Nano and Molecular Systems Research Unit, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland
| | - Tanel Käämbre
- Institute of Physics, University of Tartu, W. Ostwald Street 1, EE-51014 Tartu, Estonia
| | - Frank Siewert
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Grzegorz Gwalt
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Andrey Sokolov
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Stephanie Lemke
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Svyatoslav Alimov
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Jeniffa Knedel
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Oliver Kutz
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Tino Seliger
- BESSY-II, Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, 12489 Berlin, Germany
| | - Mika Valden
- Surface Science Group, Laboratory of Photonics, Physics Unit, Tampere University, PO Box 692, FI-33014 Tampere, Finland
| | - Mika Hirsimäki
- Surface Science Group, Laboratory of Photonics, Physics Unit, Tampere University, PO Box 692, FI-33014 Tampere, Finland
| | - Marco Kirm
- Institute of Physics, University of Tartu, W. Ostwald Street 1, EE-51014 Tartu, Estonia
| | - Marko Huttula
- Nano and Molecular Systems Research Unit, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland
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12
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Kumar P, Herath TM, Apalkov V. Bilayer graphene in strong ultrafast laser fields. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:335305. [PMID: 34126603 DOI: 10.1088/1361-648x/ac0b1e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2021] [Accepted: 06/14/2021] [Indexed: 06/12/2023]
Abstract
We theoretically investigate the interaction of an ultrastrong femtosecond-long linearly polarized optical pulse with AB-stacked bilayer graphene (BLG). The pulse excite electrons from the valence into the conduction band (CB), resulting in finite CB population. Such a redistribution of electrons results in the generation of current which can be manipulated by the angle of incidence of the pulse. For the normal incidence, the current along a direction transverse to the polarization of the optical pulse is zero. However, the interlayer symmetry is broken up by a finite angle of incidence due to which BLG possesses a single axis of symmetry. Thus, for an oblique incidence, if the pulse is polarized normal to the symmetry axis then there is an induction of electric current in the direction perpendicular to the polarization of the pulse. We show that the magnitude and the direction of such a current as well as charge transfer along this direction can be manipulated by tuning the angle of incidence of the laser pulse. Further, the symmetry of the system prohibits the generation of transverse current if the pulse is polarized along the axis of symmetry of BLG.
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Affiliation(s)
- Pardeep Kumar
- Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, United States of America
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States of America
| | - Thakshila M Herath
- Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, United States of America
| | - Vadym Apalkov
- Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, United States of America
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13
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Ünzelmann M, Bentmann H, Figgemeier T, Eck P, Neu JN, Geldiyev B, Diekmann F, Rohlf S, Buck J, Hoesch M, Kalläne M, Rossnagel K, Thomale R, Siegrist T, Sangiovanni G, Sante DD, Reinert F. Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs. Nat Commun 2021; 12:3650. [PMID: 34131129 PMCID: PMC8206138 DOI: 10.1038/s41467-021-23727-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 05/12/2021] [Indexed: 11/16/2022] Open
Abstract
Since the early days of Dirac flux quantization, magnetic monopoles have been sought after as a potential corollary of quantized electric charge. As opposed to magnetic monopoles embedded into the theory of electromagnetism, Weyl semimetals (WSM) exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the crossing point of spin-polarized bands forming the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic WSM. We carried out angle-resolved photoelectron spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. The experiments reveal large spin- and orbital-angular-momentum (SAM and OAM) polarizations of the Weyl-fermion states, resulting from the broken crystalline inversion symmetry in TaAs. Supported by first-principles calculations, our measurements image signatures of a topologically non-trivial winding of the OAM at the Weyl nodes and unveil a chirality-dependent SAM of the Weyl bands. Our results provide directly bulk-sensitive spectroscopic support for the non-trivial band topology in the WSM TaAs, promising to have profound implications for the study of quantum-geometric effects in solids. Weyl semimetals exhibit Berry flux monopoles in momentum-space, but direct experimental evidence has remained elusive. Here, the authors reveal topologically non-trivial winding of the orbital-angular-momentum at the Weyl nodes and a chirality-dependent spin-angular-momentum of the Weyl bands, as a direct signature of the Berry flux monopoles in TaAs.
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Affiliation(s)
- M Ünzelmann
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany
| | - H Bentmann
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany.
| | - T Figgemeier
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany
| | - P Eck
- Theoretische Physik I, Universität Würzburg, Würzburg, Germany
| | - J N Neu
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee, FL, USA.,National High Magnetic Field Laboratory, Tallahassee, FL, USA
| | - B Geldiyev
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany
| | - F Diekmann
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.,Ruprecht Haensel Laboratory, Kiel University and DESY, Kiel, Germany
| | - S Rohlf
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.,Ruprecht Haensel Laboratory, Kiel University and DESY, Kiel, Germany
| | - J Buck
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.,Ruprecht Haensel Laboratory, Kiel University and DESY, Kiel, Germany
| | - M Hoesch
- Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
| | - M Kalläne
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.,Ruprecht Haensel Laboratory, Kiel University and DESY, Kiel, Germany
| | - K Rossnagel
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.,Ruprecht Haensel Laboratory, Kiel University and DESY, Kiel, Germany.,Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
| | - R Thomale
- Theoretische Physik I, Universität Würzburg, Würzburg, Germany
| | - T Siegrist
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee, FL, USA.,National High Magnetic Field Laboratory, Tallahassee, FL, USA
| | - G Sangiovanni
- Theoretische Physik I, Universität Würzburg, Würzburg, Germany
| | - D Di Sante
- Theoretische Physik I, Universität Würzburg, Würzburg, Germany.,Department of Physics and Astronomy, University of Bologna, Bologna, Italy.,Center for Computational Quantum Physics, Flatiron Institute, New York, NY, USA
| | - F Reinert
- Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Würzburg, Germany
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14
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Bao C, Zhang H, Zhang T, Wu X, Luo L, Zhou S, Li Q, Hou Y, Yao W, Liu L, Yu P, Li J, Duan W, Yao H, Wang Y, Zhou S. Experimental Evidence of Chiral Symmetry Breaking in Kekulé-Ordered Graphene. PHYSICAL REVIEW LETTERS 2021; 126:206804. [PMID: 34110212 DOI: 10.1103/physrevlett.126.206804] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Accepted: 03/30/2021] [Indexed: 06/12/2023]
Abstract
The low-energy excitations of graphene are relativistic massless Dirac fermions with opposite chiralities at valleys K and K^{'}. Breaking the chiral symmetry could lead to gap opening in analogy to dynamical mass generation in particle physics. Here we report direct experimental evidences of chiral symmetry breaking (CSB) from both microscopic and spectroscopic measurements in a Li-intercalated graphene. The CSB is evidenced by gap opening at the Dirac point, Kekulé-O type modulation, and chirality mixing near the gap edge. Our work opens up opportunities for investigating CSB related physics in a Kekulé-ordered graphene.
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Affiliation(s)
- Changhua Bao
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
| | - Hongyun Zhang
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
| | - Teng Zhang
- School of Information and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, Beijing 100081, People's Republic of China
| | - Xi Wu
- Shenzhen Geim Graphene Center and Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, People's Republic of China
| | - Laipeng Luo
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
| | - Shaohua Zhou
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
| | - Qian Li
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
| | - Yanhui Hou
- School of Information and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, Beijing 100081, People's Republic of China
| | - Wei Yao
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
| | - Liwei Liu
- School of Information and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, Beijing 100081, People's Republic of China
| | - Pu Yu
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
- Frontier Science Center for Quantum Information, Beijing 100084, People's Republic of China
| | - Jia Li
- Shenzhen Geim Graphene Center and Institute of Materials Research, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, People's Republic of China
| | - Wenhui Duan
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
- Frontier Science Center for Quantum Information, Beijing 100084, People's Republic of China
| | - Hong Yao
- Institute for Advanced Study, Tsinghua University, Beijing 100084, People's Republic of China
- Department of Physics, Stanford University, Stanford, California 94305, USA
| | - Yeliang Wang
- School of Information and Electronics, MIIT Key Laboratory for Low-Dimensional Quantum Structure and Devices, Beijing Institute of Technology, Beijing 100081, People's Republic of China
| | - Shuyun Zhou
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, People's Republic of China
- Frontier Science Center for Quantum Information, Beijing 100084, People's Republic of China
- Beijing Advanced Innovation Center for Future Chip, Beijing 100084, People's Republic of China
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15
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Ab Initio Theory of Photoemission from Graphene. NANOMATERIALS 2021; 11:nano11051212. [PMID: 34063600 PMCID: PMC8147655 DOI: 10.3390/nano11051212] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/28/2021] [Accepted: 04/30/2021] [Indexed: 11/17/2022]
Abstract
Angle-resolved photoemission from monolayer and bilayer graphene is studied based on an ab initio one-step theory. The outgoing photoelectron is represented by the time-reversed low energy electron diffraction (LEED) state ΦLEED*, which is calculated using a scattering theory formulated in terms of augmented plane waves. A strong enhancement of the emission intensity is found to occur around the scattering resonances. The effect of the photoelectron scattering by the underlying substrate on the polarization dependence of the photocurrent is discussed. The constant initial state spectra I(k||,ℏω) are compared to electron transmission spectra T(E) of graphene, and the spatial structure of the outgoing waves is analyzed. It turns out that the emission intensity variations do not correlate with the structure of the T(E) spectra and are caused by rather subtle interference effects. Earlier experimental observations of the photon energy and polarization dependence of the emission intensity I(k||,ℏω) are well reproduced within the dipole approximation, and the Kohn-Sham eigenstates are found to provide a quite reasonable description of the photoemission final states.
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16
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Beaulieu S, Schusser J, Dong S, Schüler M, Pincelli T, Dendzik M, Maklar J, Neef A, Ebert H, Hricovini K, Wolf M, Braun J, Rettig L, Minár J, Ernstorfer R. Revealing Hidden Orbital Pseudospin Texture with Time-Reversal Dichroism in Photoelectron Angular Distributions. PHYSICAL REVIEW LETTERS 2020; 125:216404. [PMID: 33274965 DOI: 10.1103/physrevlett.125.216404] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 10/13/2020] [Indexed: 06/12/2023]
Abstract
We performed angle-resolved photoemission spectroscopy (ARPES) of bulk 2H-WSe_{2} for different crystal orientations linked to each other by time-reversal symmetry. We introduce a new observable called time-reversal dichroism in photoelectron angular distributions (TRDAD), which quantifies the modulation of the photoemission intensity upon effective time-reversal operation. We demonstrate that the hidden orbital pseudospin texture leaves its imprint on TRDAD, due to multiple orbital interference effects in photoemission. Our experimental results are in quantitative agreement with both the tight-binding model and state-of-the-art fully relativistic calculations performed using the one-step model of photoemission. While spin-resolved ARPES probes the spin component of entangled spin-orbital texture in multiorbital systems, we unambiguously demonstrate that TRDAD reveals its orbital pseudospin texture counterpart.
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Affiliation(s)
- S Beaulieu
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - J Schusser
- Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
- New Technologies-Research Center, University of West Bohemia, 30614 Pilsen, Czech Republic
| | - S Dong
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - M Schüler
- Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - T Pincelli
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - M Dendzik
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
- Department of Applied Physics, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19 Stockholm, Sweden
| | - J Maklar
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - A Neef
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - H Ebert
- Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 11, 81377 München, Germany
| | - K Hricovini
- Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
- LIDYL, CEA, CNRS, Université Paris-Saclay, CEA Saclay, F-91191 Gif-sur-Yvette Cedex, France
| | - M Wolf
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - J Braun
- Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstrasse 11, 81377 München, Germany
| | - L Rettig
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - J Minár
- New Technologies-Research Center, University of West Bohemia, 30614 Pilsen, Czech Republic
| | - R Ernstorfer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
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17
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Kang M, Fang S, Ye L, Po HC, Denlinger J, Jozwiak C, Bostwick A, Rotenberg E, Kaxiras E, Checkelsky JG, Comin R. Topological flat bands in frustrated kagome lattice CoSn. Nat Commun 2020; 11:4004. [PMID: 32778669 PMCID: PMC7417556 DOI: 10.1038/s41467-020-17465-1] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2020] [Accepted: 06/30/2020] [Indexed: 11/08/2022] Open
Abstract
Electronic flat bands in momentum space, arising from strong localization of electrons in real space, are an ideal stage to realize strongly-correlated phenomena. Theoretically, the flat bands can naturally arise in certain geometrically frustrated lattices, often with nontrivial topology if combined with spin-orbit coupling. Here, we report the observation of topological flat bands in frustrated kagome metal CoSn, using angle-resolved photoemission spectroscopy and band structure calculations. Throughout the entire Brillouin zone, the bandwidth of the flat band is suppressed by an order of magnitude compared to the Dirac bands originating from the same orbitals. The frustration-driven nature of the flat band is directly confirmed by the chiral d-orbital texture of the corresponding real-space Wannier functions. Spin-orbit coupling opens a large gap of 80 meV at the quadratic touching point between the Dirac and flat bands, endowing a nonzero Z2 invariant to the flat band. These findings demonstrate that kagome-derived flat bands are a promising platform for novel emergent phases of matter at the confluence of strong correlation and topology.
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Affiliation(s)
- Mingu Kang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Shiang Fang
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
- John A. Paulson School of Engineering and Applied Science, Harvard University, Cambridge, MA, 02138, USA
- Department of Physics and Astronomy, Center for Materials Theory, Rutgers University, Piscataway, NJ, 08854, USA
| | - Linda Ye
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Hoi Chun Po
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Jonathan Denlinger
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Chris Jozwiak
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Aaron Bostwick
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Eli Rotenberg
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Efthimios Kaxiras
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
- John A. Paulson School of Engineering and Applied Science, Harvard University, Cambridge, MA, 02138, USA
| | - Joseph G Checkelsky
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Riccardo Comin
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
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18
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Galeotti G, De Marchi F, Hamzehpoor E, MacLean O, Rajeswara Rao M, Chen Y, Besteiro LV, Dettmann D, Ferrari L, Frezza F, Sheverdyaeva PM, Liu R, Kundu AK, Moras P, Ebrahimi M, Gallagher MC, Rosei F, Perepichka DF, Contini G. Synthesis of mesoscale ordered two-dimensional π-conjugated polymers with semiconducting properties. NATURE MATERIALS 2020; 19:874-880. [PMID: 32424372 DOI: 10.1038/s41563-020-0682-z] [Citation(s) in RCA: 104] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Accepted: 04/14/2020] [Indexed: 05/08/2023]
Abstract
Two-dimensional materials with high charge carrier mobility and tunable band gaps have attracted intense research effort for their potential use in nanoelectronics. Two-dimensional π-conjugated polymers constitute a promising subclass because the band structure can be manipulated by varying the molecular building blocks while preserving key features such as Dirac cones and high charge mobility. The major barriers to the application of two-dimensional π-conjugated polymers have been the small domain size and high defect density attained in the syntheses explored so far. Here, we demonstrate the fabrication of mesoscale ordered two-dimensional π-conjugated polymer kagome lattices with semiconducting properties, Dirac cone structures and flat bands on Au(111). This material has been obtained by combining a rigid azatriangulene precursor and a hot dosing approach, which favours molecular diffusion and eliminates voids in the network. These results open opportunities for the synthesis of two-dimensional π-conjugated polymer Dirac cone materials and their integration into devices.
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Affiliation(s)
- G Galeotti
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada
- Istituto di Struttura della Materia, CNR, Roma, Italy
- Deutsches Museum, München, Germany
| | - F De Marchi
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada
| | - E Hamzehpoor
- Department of Chemistry, McGill University, Montreal, Québec, Canada
| | - O MacLean
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada
| | - M Rajeswara Rao
- Department of Chemistry, McGill University, Montreal, Québec, Canada
| | - Y Chen
- Department of Chemistry, McGill University, Montreal, Québec, Canada
| | - L V Besteiro
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China
| | - D Dettmann
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada
- Istituto di Struttura della Materia, CNR, Roma, Italy
| | - L Ferrari
- Istituto di Struttura della Materia, CNR, Roma, Italy
| | - F Frezza
- Istituto di Struttura della Materia, CNR, Roma, Italy
- Department of Physics, University of Tor Vergata, Rome, Italy
| | | | - R Liu
- Department of Physics, Lakehead University, Thunder Bay, Ontario, Canada
| | - A K Kundu
- Istituto di Struttura della Materia, CNR, Trieste, Italy
| | - P Moras
- Istituto di Struttura della Materia, CNR, Trieste, Italy
| | - M Ebrahimi
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada
- Department of Chemistry, Lakehead University, Thunder Bay, Ontario, Canada
| | - M C Gallagher
- Department of Physics, Lakehead University, Thunder Bay, Ontario, Canada.
| | - F Rosei
- Centre Energie, Matériaux et Télécommunications, Institut National de la Recherche Scientifique, Varennes, Québec, Canada.
| | - D F Perepichka
- Department of Chemistry, McGill University, Montreal, Québec, Canada.
| | - G Contini
- Istituto di Struttura della Materia, CNR, Roma, Italy.
- Department of Physics, University of Tor Vergata, Rome, Italy.
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19
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Pashalou S, Goudarzi H, Khezerlou M. Ultrafast electron dynamics in monolayer MoS 2interacting with optical pulse influenced by exchange field and waveform. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:355403. [PMID: 32330913 DOI: 10.1088/1361-648x/ab8cdc] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Accepted: 04/24/2020] [Indexed: 06/11/2023]
Abstract
In this paper, we investigate the effect of waveform and carrier-envelope phase on the electron dynamics in monolayer MoS2interacting with an ultrashort (few-femtosecond) optical pulse in the presence of magnetic exchange field. The waveform of the zero area pulse is characterized by Hermite-Gaussian polynomials associated with time-dependent and carrier-envelope phases. Because the duration of optical pulse is less than the characteristic electron scattering time (10-100 fs), the electron dynamics is coherent, and can be described by the time-dependent Schrödinger equation. We show, that the electron transition from valence band to conduction band is a deeply irreversible dynamics, which implies quantum electron dynamics is highly nonadiabatic. We study the effect of carrier-envelope phase and exchange field on the conduction band population for two types of waveform. Electron distribution in reciprocal space gives asymmetric hot spots in differentKandK' valleys after the pulse ends (valley polarization effect), which is found to be more sensitive to carrier-envelope phase. The predicted effect provides new opportunities for the improvement of information processing in the petahertz domain and optoelectronics applications.
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Affiliation(s)
- S Pashalou
- Department of Physics, Faculty of Science, Urmia University, P.O. Box: 165, Urmia, Iran
| | - H Goudarzi
- Department of Physics, Faculty of Science, Urmia University, P.O. Box: 165, Urmia, Iran
| | - M Khezerlou
- Engineering Faculty of Khoy, Urmia University, P.O. Box: 165, Urmia, Iran
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20
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Jung SW, Ryu SH, Shin WJ, Sohn Y, Huh M, Koch RJ, Jozwiak C, Rotenberg E, Bostwick A, Kim KS. Black phosphorus as a bipolar pseudospin semiconductor. NATURE MATERIALS 2020; 19:277-281. [PMID: 32015535 DOI: 10.1038/s41563-019-0590-2] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 12/15/2019] [Indexed: 06/10/2023]
Abstract
Semiconductor devices rely on the charge and spin of electrons, but there is another electronic degree of freedom called pseudospin in a two-level quantum system1 such as a crystal consisting of two sublattices2. A potential way to exploit the pseudospin of electrons in pseudospintronics3-5 is to find quantum matter with tunable and sizeable pseudospin polarization. Here, we propose a bipolar pseudospin semiconductor, where the electron and hole states have opposite net pseudospin polarization. We experimentally identify such states in anisotropic honeycomb crystal-black phosphorus. By sublattice interference of photoelectrons, we find bipolar pseudospin polarization greater than 95% that is stable at room temperature. This pseudospin polarization is identified as a consequence of Dirac cones merged in the highly anisotropic honeycomb system6,7. The bipolar pseudospin semiconductor, which is a pseudospin analogue of magnetic semiconductors, is not only interesting in itself, but also might be useful for pseudospintronics.
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Affiliation(s)
- Sung Won Jung
- Department of Physics, Yonsei University, Seoul, Korea
- Diamond Light Source, Didcot, UK
| | - Sae Hee Ryu
- Department of Physics, Yonsei University, Seoul, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
| | - Woo Jong Shin
- Department of Physics, Yonsei University, Seoul, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
| | - Yeongsup Sohn
- Department of Physics, Yonsei University, Seoul, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
| | - Minjae Huh
- Department of Physics, Yonsei University, Seoul, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang, Korea
| | - Roland J Koch
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Chris Jozwiak
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Eli Rotenberg
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Aaron Bostwick
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Keun Su Kim
- Department of Physics, Yonsei University, Seoul, Korea.
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21
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Oliaei Motlagh SA, Nematollahi F, Mitra A, Zafar AJ, Apalkov V, Stockman MI. Ultrafast optical currents in gapped graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:065305. [PMID: 31634884 DOI: 10.1088/1361-648x/ab4fc7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We theoretically study the interaction of ultrashort optical pulses with gapped graphene. Such a strong pulse results in a finite conduction band population and a corresponding electric current, both during and after the pulse. Since gapped graphene has broken inversion symmetry, it has an axial symmetry about the y -axis but not about the x-axis. We show that, in this case, if the linear pulse is polarized along the x-axis, the rectified electric current is generated in the y direction. At the same time, the conduction band population distribution in the reciprocal space is symmetric about the x-axis. Thus, the rectified current in gapped graphene has an inter-band origin, while the intra-band contribution to the rectified current is zero.
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Affiliation(s)
- S Azar Oliaei Motlagh
- Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, United States of America
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22
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Kang M, Ye L, Fang S, You JS, Levitan A, Han M, Facio JI, Jozwiak C, Bostwick A, Rotenberg E, Chan MK, McDonald RD, Graf D, Kaznatcheev K, Vescovo E, Bell DC, Kaxiras E, van den Brink J, Richter M, Prasad Ghimire M, Checkelsky JG, Comin R. Dirac fermions and flat bands in the ideal kagome metal FeSn. NATURE MATERIALS 2020; 19:163-169. [PMID: 31819211 DOI: 10.1038/s41563-019-0531-0] [Citation(s) in RCA: 100] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Accepted: 10/08/2019] [Indexed: 06/10/2023]
Abstract
A kagome lattice of 3d transition metal ions is a versatile platform for correlated topological phases hosting symmetry-protected electronic excitations and magnetic ground states. However, the paradigmatic states of the idealized two-dimensional kagome lattice-Dirac fermions and flat bands-have not been simultaneously observed. Here, we use angle-resolved photoemission spectroscopy and de Haas-van Alphen quantum oscillations to reveal coexisting surface and bulk Dirac fermions as well as flat bands in the antiferromagnetic kagome metal FeSn, which has spatially decoupled kagome planes. Our band structure calculations and matrix element simulations demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals, and evidence that the coexisting Dirac surface state realizes a rare example of fully spin-polarized two-dimensional Dirac fermions due to spin-layer locking in FeSn. The prospect to harness these prototypical excitations in a kagome lattice is a frontier of great promise at the confluence of topology, magnetism and strongly correlated physics.
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Affiliation(s)
- Mingu Kang
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Linda Ye
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Shiang Fang
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Jhih-Shih You
- Leibniz Institute for Solid State and Materials Research, IFW Dresden, Dresden, Germany
| | - Abe Levitan
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Minyong Han
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Jorge I Facio
- Leibniz Institute for Solid State and Materials Research, IFW Dresden, Dresden, Germany
| | - Chris Jozwiak
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Aaron Bostwick
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Eli Rotenberg
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Mun K Chan
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - Ross D McDonald
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, NM, USA
| | - David Graf
- National High Magnetic Field Laboratory, Tallahassee, FL, USA
| | | | - Elio Vescovo
- National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, USA
| | - David C Bell
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
- Center for Nanoscale systems, Harvard University, Cambridge, MA, 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
| | - Jeroen van den Brink
- Leibniz Institute for Solid State and Materials Research, IFW Dresden, Dresden, Germany
| | - Manuel Richter
- Leibniz Institute for Solid State and Materials Research, IFW Dresden, Dresden, Germany
- Dresden Center for Computational Materials Science (DCMS), TU Dresden, Dresden, Germany
| | - Madhav Prasad Ghimire
- Leibniz Institute for Solid State and Materials Research, IFW Dresden, Dresden, Germany
- Central Department of Physics, Tribhuvan University, Kirtipur, Kathmandu, Nepal
| | - Joseph G Checkelsky
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Riccardo Comin
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, USA.
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23
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Schüler M, De Giovannini U, Hübener H, Rubio A, Sentef MA, Werner P. Local Berry curvature signatures in dichroic angle-resolved photoelectron spectroscopy from two-dimensional materials. SCIENCE ADVANCES 2020; 6:eaay2730. [PMID: 32158939 PMCID: PMC7048418 DOI: 10.1126/sciadv.aay2730] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Accepted: 12/04/2019] [Indexed: 06/07/2023]
Abstract
Topologically nontrivial two-dimensional materials hold great promise for next-generation optoelectronic applications. However, measuring the Hall or spin-Hall response is often a challenge and practically limited to the ground state. An experimental technique for tracing the topological character in a differential fashion would provide useful insights. In this work, we show that circular dichroism angle-resolved photoelectron spectroscopy provides a powerful tool that can resolve the topological and quantum-geometrical character in momentum space. In particular, we investigate how to map out the signatures of the momentum-resolved Berry curvature in two-dimensional materials by exploiting its intimate connection to the orbital polarization. A spin-resolved detection of the photoelectrons allows one to extend the approach to spin-Chern insulators. The present proposal can be extended to address topological properties in materials out of equilibrium in a time-resolved fashion.
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Affiliation(s)
- Michael Schüler
- Stanford Institute for Materials and Energy Sciences (SIMES), SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
- Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
| | - Umberto De Giovannini
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Hannes Hübener
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Angel Rubio
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
- Center for Computational Quantum Physics (CCQ), The Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
| | - Michael A. Sentef
- Max Planck Institute for the Structure and Dynamics of Matter, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Philipp Werner
- Department of Physics, University of Fribourg, 1700 Fribourg, Switzerland
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24
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Na MX, Mills AK, Boschini F, Michiardi M, Nosarzewski B, Day RP, Razzoli E, Sheyerman A, Schneider M, Levy G, Zhdanovich S, Devereaux TP, Kemper AF, Jones DJ, Damascelli A. Direct determination of mode-projected electron-phonon coupling in the time domain. Science 2019; 366:1231-1236. [DOI: 10.1126/science.aaw1662] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Accepted: 11/05/2019] [Indexed: 11/02/2022]
Abstract
Ultrafast spectroscopies have become an important tool for elucidating the microscopic description and dynamical properties of quantum materials. In particular, by tracking the dynamics of nonthermal electrons, a material’s dominant scattering processes can be revealed. Here, we present a method for extracting the electron-phonon coupling strength in the time domain, using time- and angle-resolved photoemission spectroscopy (TR-ARPES). This method is demonstrated in graphite, where we investigate the dynamics of photoinjected electrons at the K¯ point, detecting quantized energy-loss processes that correspond to the emission of strongly coupled optical phonons. We show that the observed characteristic time scale for spectral weight transfer mediated by phonon-scattering processes allows for the direct quantitative extraction of electron-phonon matrix elements for specific modes.
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Affiliation(s)
- M. X. Na
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - A. K. Mills
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - F. Boschini
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - M. Michiardi
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - B. Nosarzewski
- Department of Materials Science and Engineering, Stanford Institute for Materials and Energy Sciences, Stanford, CA 94305, USA
| | - R. P. Day
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - E. Razzoli
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - A. Sheyerman
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - M. Schneider
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - G. Levy
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - S. Zhdanovich
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - T. P. Devereaux
- Department of Materials Science and Engineering, Stanford Institute for Materials and Energy Sciences, Stanford, CA 94305, USA
| | - A. F. Kemper
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA
| | - D. J. Jones
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
| | - A. Damascelli
- Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Quantum Matter Institute, Vancouver, BC V6T 1Z4, Canada
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25
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Song D, Leykam D, Su J, Liu X, Tang L, Liu S, Zhao J, Efremidis NK, Xu J, Chen Z. Valley Vortex States and Degeneracy Lifting via Photonic Higher-Band Excitation. PHYSICAL REVIEW LETTERS 2019; 122:123903. [PMID: 30978034 DOI: 10.1103/physrevlett.122.123903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Indexed: 06/09/2023]
Abstract
We demonstrate valley-dependent vortex generation in photonic graphene. Without breaking inversion symmetry, the excitation of two valleys leads to the formation of an optical vortex upon Bragg reflection to the third equivalent valley, with its chirality determined by the valley degree of freedom. Vortex-antivortex pairs with valley-dependent topological charge flipping are also observed and corroborated by numerical simulations. Furthermore, we develop a three-band effective Hamiltonian model to describe the dynamics of the coupled valleys and find that the commonly used two-band model is not sufficient to explain the observed vortex degeneracy lifting. Such valley-polarized vortex states arise from high-band excitation without a synthetic-field-induced gap opening. Our results from a photonic setting may provide insight for the study of valley contrasting and Berry-phase-mediated topological phenomena in other systems.
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Affiliation(s)
- Daohong Song
- The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Daniel Leykam
- Center for Theoretical Physics of Complex Systems, Institute for Basic Science, Daejeon 34126, Republic of Korea
| | - Jing Su
- The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
| | - Xiuying Liu
- The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
| | - Liqin Tang
- The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
| | - Sheng Liu
- The Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education and School of Science, Northwestern Polytechnical University, Xi'an 710072, China
| | - Jianlin Zhao
- The Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education and School of Science, Northwestern Polytechnical University, Xi'an 710072, China
| | - Nikolaos K Efremidis
- Department of Mathematics and Applied Mathematics, University of Crete, 70013 Heraklion, Crete, Greece
| | - Jingjun Xu
- The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
| | - Zhigang Chen
- The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
- Department of Physics and Astronomy, San Francisco State University, San Francisco, California 94132, USA
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26
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Cho S, Park JH, Hong J, Jung J, Kim BS, Han G, Kyung W, Kim Y, Mo SK, Denlinger JD, Shim JH, Han JH, Kim C, Park SR. Experimental Observation of Hidden Berry Curvature in Inversion-Symmetric Bulk 2H-WSe_{2}. PHYSICAL REVIEW LETTERS 2018; 121:186401. [PMID: 30444409 DOI: 10.1103/physrevlett.121.186401] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 08/24/2018] [Indexed: 06/09/2023]
Abstract
We investigate the hidden Berry curvature in bulk 2H-WSe_{2} by utilizing the surface sensitivity of angle resolved photoemission (ARPES). The symmetry in the electronic structure of transition metal dichalcogenides is used to uniquely determine the local orbital angular momentum (OAM) contribution to the circular dichroism (CD) in ARPES. The extracted CD signals for the K and K^{'} valleys are almost identical, but their signs, which should be determined by the valley index, are opposite. In addition, the sign is found to be the same for the two spin-split bands, indicating that it is independent of spin state. These observed CD behaviors are what are expected from Berry curvature of a monolayer of WSe_{2}. In order to see if CD-ARPES is indeed representative of hidden Berry curvature within a layer, we use tight binding analysis as well as density functional calculation to calculate the Berry curvature and local OAM of a monolayer WSe_{2}. We find that measured CD-ARPES is approximately proportional to the calculated Berry curvature as well as local OAM, further supporting our interpretation.
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Affiliation(s)
- Soohyun Cho
- Institute of Physics and Applied Physics, Yonsei University, Seoul 03722, Korea
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
| | - Jin-Hong Park
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
| | - Jisook Hong
- Department of Chemistry, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Jongkeun Jung
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Republic of Korea
| | - Beom Seo Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Republic of Korea
| | - Garam Han
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Republic of Korea
| | - Wonshik Kyung
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Republic of Korea
- Advanced Light Source, Lawrence Berkeley National Laboratory, California 94720, USA
| | - Yeongkwan Kim
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea
| | - S-K Mo
- Advanced Light Source, Lawrence Berkeley National Laboratory, California 94720, USA
| | - J D Denlinger
- Advanced Light Source, Lawrence Berkeley National Laboratory, California 94720, USA
| | - Ji Hoon Shim
- Department of Chemistry, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
- Department of Physics and Division of Advanced Nuclear Engineering, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
| | - Jung Hoon Han
- Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea
| | - Changyoung Kim
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea
- Department of Physics and Astronomy, Seoul National University (SNU), Seoul 08826, Republic of Korea
| | - Seung Ryong Park
- Department of Physics, Incheon National University, Incheon 22012, Republic of Korea
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27
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Du R, Liu MH, Mohrmann J, Wu F, Krupke R, von Löhneysen H, Richter K, Danneau R. Tuning Anti-Klein to Klein Tunneling in Bilayer Graphene. PHYSICAL REVIEW LETTERS 2018; 121:127706. [PMID: 30296148 DOI: 10.1103/physrevlett.121.127706] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 07/15/2018] [Indexed: 06/08/2023]
Abstract
We show that in gapped bilayer graphene, quasiparticle tunneling and the corresponding Berry phase can be controlled such that they exhibit features of single-layer graphene such as Klein tunneling. The Berry phase is detected by a high-quality Fabry-Pérot interferometer based on bilayer graphene. By raising the Fermi energy of the charge carriers, we find that the Berry phase can be continuously tuned from 2π down to 0.68π in gapped bilayer graphene, in contrast to the constant Berry phase of 2π in pristine bilayer graphene. Particularly, we observe a Berry phase of π, the standard value for single-layer graphene. As the Berry phase decreases, the corresponding transmission probability of charge carriers at normal incidence clearly demonstrates a transition from anti-Klein tunneling to nearly perfect Klein tunneling.
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Affiliation(s)
- Renjun Du
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
| | - Ming-Hao Liu
- Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Jens Mohrmann
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
| | - Fan Wu
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
- College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
| | - Ralph Krupke
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
- Institute of Material Science, Technische Universität Darmstadt, D-64287 Darmstadt, Germany
| | - Hilbert von Löhneysen
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
- Institute for Solid State Physics and Physics Institute, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
| | - Klaus Richter
- Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany
| | - Romain Danneau
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany
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28
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Lee CC, Fukuda M, Lee YT, Ozaki T. Realization of intrinsically broken Dirac cones in graphene via the momentum-resolved electronic band structure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:295502. [PMID: 29873298 DOI: 10.1088/1361-648x/aacac2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A way to represent the band structure that distinguishes between energy-momentum and energy-crystal momentum relationships is proposed upon the band-unfolding concept. This momentum-resolved band structure offers better understanding of the physical processes requiring the information of wave functions in momentum space and provides a direct connection to angle-resolved photoelectron spectroscopy (ARPES) spectra. Following this approach, we demonstrate that Dirac cones in graphene are intrinsically broken in momentum space and can be described by a conceptual unit cell smaller than the primitive unit cell. This hidden degree of freedom can be measured by ARPES experiments as missing weight that is retrievable by investigating the effect of different polarized light. Having the energy-momentum relationship, we provide alternative understanding of the retrieved momentum intensity beyond the periodic-zone scheme, that is, the retrieved momentum intensity is assisted with the properties of final states, not from the Dirac cones directly. The revealed broken Dirac cones and momenta supplied by the lattice give interesting ingredients for designing advanced nanodevices.
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29
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Visualising Berry phase and diabolical points in a quantum exciton-polariton billiard. Sci Rep 2016; 6:37653. [PMID: 27886222 PMCID: PMC5122880 DOI: 10.1038/srep37653] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 11/01/2016] [Indexed: 11/08/2022] Open
Abstract
Diabolical points (spectral degeneracies) can naturally occur in spectra of two-dimensional quantum systems and classical wave resonators due to simple symmetries. Geometric Berry phase is associated with these spectral degeneracies. Here, we demonstrate a diabolical point and the corresponding Berry phase in the spectrum of hybrid light-matter quasiparticles-exciton-polaritons in semiconductor microcavities. It is well known that sufficiently strong optical pumping can drive exciton-polaritons to quantum degeneracy, whereby they form a macroscopically populated quantum coherent state similar to a Bose-Einstein condensate. By pumping a microcavity with a spatially structured light beam, we create a two-dimensional quantum billiard for the exciton-polariton condensate and demonstrate a diabolical point in the spectrum of the billiard eigenstates. The fully reconfigurable geometry of the potential walls controlled by the optical pump enables a striking experimental visualization of the Berry phase associated with the diabolical point. The Berry phase is observed and measured by direct imaging of the macroscopic exciton-polariton probability densities.
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Photo-electrons unveil topological transitions in graphene-like systems. Sci Rep 2016; 6:36577. [PMID: 27833125 PMCID: PMC5105119 DOI: 10.1038/srep36577] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 10/12/2016] [Indexed: 11/12/2022] Open
Abstract
The topological structure of the wavefunctions of particles in periodic potentials is characterized by the Berry curvature Ωkn whose integral on the Brillouin zone is a topological invariant known as the Chern number. The bulk-boundary correspondence states that these numbers define the number of edge or surface topologically protected states. It is then of primary interest to find experimental techniques able to measure the Berry curvature. However, up to now, there are no spectroscopic experiments that proved to be capable to obtain information on Ωkn to distinguish different topological structures of the bulk wavefunctions of semiconducting materials. Based on experimental results of the dipolar matrix elements for graphene, here we show that ARPES experiments with the appropriate x-ray energies and polarization can unambiguously detect changes of the Chern numbers in dynamically driven graphene and graphene-like materials opening new routes towards the experimental study of topological properties of condensed matter systems.
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Reich DM, Madsen LB. Illuminating Molecular Symmetries with Bicircular High-Order-Harmonic Generation. PHYSICAL REVIEW LETTERS 2016; 117:133902. [PMID: 27715131 DOI: 10.1103/physrevlett.117.133902] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Indexed: 05/10/2023]
Abstract
We present a general theory of bicircular high-order-harmonic generation from N-fold rotationally symmetric molecules. Using a rotating frame of reference we predict the complete structure of the high-order-harmonic spectra for arbitrary driving frequency ratios and show how molecular symmetries can be directly identified from the harmonic signal. Our findings reveal that a characteristic fingerprint of rotational molecular symmetries can be universally observed in the ultrafast response of molecules to strong bicircular fields.
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Affiliation(s)
- Daniel M Reich
- Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Lars Bojer Madsen
- Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
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Tanabe I, Komesu T, Le D, Rawal TB, Schwier EF, Zheng M, Kojima Y, Iwasawa H, Shimada K, Rahman TS, Dowben PA. The symmetry-resolved electronic structure of 2H-WSe2(0 0 0 1). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:345503. [PMID: 27362263 DOI: 10.1088/0953-8984/28/34/345503] [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
The orbital symmetry of the band structure of 2H-WSe2(0 0 0 1) has been investigated by means of angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT). The WSe2(0 0 0 1) experimental band structure is found, by ARPES, to be significantly different for states of even and odd reflection parities along both the [Formula: see text]-[Formula: see text] and [Formula: see text]-[Formula: see text] lines, in good agreement with results obtained from DFT. The light polarization dependence of the photoemission intensities from the top of the valence band for bulk WSe2(0 0 0 1) is explained by the dominance of W 5[Formula: see text] states around the [Formula: see text]-point and W 5d xy states around the [Formula: see text]-point, thus dominated, respectively, by states of even and odd symmetry, with respect to the [Formula: see text]-[Formula: see text] line. The splitting of the topmost valence band at [Formula: see text], due to spin-orbit coupling, is measured to be 0.49 ± 0.01 eV, in agreement with the 0.48 eV value from DFT, and prior measurements for the bulk single crystal WSe2(0 0 0 1), albeit slightly smaller than the 0.513 ± 0.01 eV observed for monolayer WSe2.
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Affiliation(s)
- Iori Tanabe
- Department of Physics and Astronomy, Theodore Jorgensen Hall, 855 N 16th, University of Nebraska, Lincoln, NE 68588-0299, USA
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Jung SW, Shin WJ, Kim J, Moreschini L, Yeom HW, Rotenberg E, Bostwick A, Kim KS. Sublattice Interference as the Origin of σ Band Kinks in Graphene. PHYSICAL REVIEW LETTERS 2016; 116:186802. [PMID: 27203340 DOI: 10.1103/physrevlett.116.186802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Indexed: 06/05/2023]
Abstract
Kinks near the Fermi level observed in angle-resolved photoemission spectroscopy (ARPES) have been widely accepted to represent electronic coupling to collective excitations, but kinks at higher energies have eluded a unified description. We identify the mechanism leading to such kink features by means of ARPES and tight-binding band calculations on σ bands of graphene, where anomalous kinks at energies as high as ∼4 eV were reported recently [Phys. Rev. Lett. 111, 216806 (2013)]. We found that two σ bands show a strong intensity modulation with abruptly vanishing intensity near the kink features, which is due to sublattice interference. The interference induced local singularity in the matrix element is a critical factor that gives rise to apparent kink features, as confirmed by our spectral simulations without involving any coupling to collective excitations.
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Affiliation(s)
- Sung Won Jung
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Woo Jong Shin
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Jimin Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Luca Moreschini
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Han Woong Yeom
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Eli Rotenberg
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Aaron Bostwick
- Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Keun Su Kim
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science, Pohang 37673, Korea
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea
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Ma G, Yu W, Yu MY, Shen B, Veisz L. Intense circularly polarized attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses. OPTICS EXPRESS 2016; 24:10057-10065. [PMID: 27137616 DOI: 10.1364/oe.24.010057] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We have investigated the polarization of attosecond light pulses generated from relativistic few-cycle laser pulse interaction with the surface of overdense plasmas using particle-in-cell simulation. Under suitable conditions, a desired polarization state of the generated attosecond pulse can be achieved by controlling the polarization of the incident laser. In particular, an elliptically polarized laser pulse of suitable ellipticity can generate an almost circularly polarized attosecond pulse without compromising the harmonic generation efficiency. The process is thus applicable as a new tabletop circularly-polarized XUV radiation source for probing attosecond phenomena with high temporal resolution.
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Van Tuan D, Roche S. Spin Manipulation in Graphene by Chemically Induced Pseudospin Polarization. PHYSICAL REVIEW LETTERS 2016; 116:106601. [PMID: 27015500 DOI: 10.1103/physrevlett.116.106601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Indexed: 06/05/2023]
Abstract
Spin manipulation is one of the most critical challenges to realize spin-based logic devices and spintronic circuits. Graphene has been heralded as an ideal material to achieve spin manipulation, but so far new paradigms and demonstrators are limited. Here we show that certain impurities such as fluorine adatoms, which locally break sublattice symmetry without the formation of strong magnetic moment, could result in a remarkable variability of spin transport characteristics. The impurity resonance level is found to be associated with a long-range sublattice pseudospin polarization, which by locally decoupling spin and pseudospin dynamics provokes a huge spin lifetime electron-hole asymmetry. In the dilute impurity limit, spin lifetimes could be tuned electrostatically from 100 ps to several nanoseconds, providing a protocol to chemically engineer an unprecedented spin device functionality.
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Affiliation(s)
- Dinh Van Tuan
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, 08193 Barcelona, Spain
| | - Stephan Roche
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, 08193 Barcelona, Spain
- ICREA, Institució Catalana de Recerca i Estudis Avançats, 08070 Barcelona, Spain
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Schmidt J, Guggenmos A, Hofstetter M, Chew SH, Kleineberg U. Generation of circularly polarized high harmonic radiation using a transmission multilayer quarter waveplate. OPTICS EXPRESS 2015; 23:33564-33578. [PMID: 26832020 DOI: 10.1364/oe.23.033564] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
High harmonic radiation is meanwhile nearly extensively used for the spectroscopic investigation of electron dynamics with ultimate time resolution. The majority of high harmonic beamlines provide linearly polarized radiation created in a gas target. However, circular polarization greatly extends the spectroscopic possibilities for high harmonics, especially in the analysis of samples with chirality or prominent spin polarization. We produced a free-standing multilayer foil as a transmission EUV quarter waveplate and applied it for the first time to high harmonic radiation. We measured a broadband (4.6 eV FWHM) ellipticity of 75% at 66 eV photon energy with a transmission efficiency of 5%. The helicity is switchable and the ellipticity can be adjusted to lower values by angle tuning. As a single element it can be easily integrated in any existing harmonic beamline without major changes.
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Unveiling pseudospin and angular momentum in photonic graphene. Nat Commun 2015; 6:6272. [PMID: 25687645 DOI: 10.1038/ncomms7272] [Citation(s) in RCA: 99] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Accepted: 01/12/2015] [Indexed: 11/08/2022] Open
Abstract
Pseudospin, an additional degree of freedom inherent in graphene, plays a key role in understanding many fundamental phenomena such as the anomalous quantum Hall effect, electron chirality and Klein paradox. Unlike the electron spin, the pseudospin was traditionally considered as an unmeasurable quantity, immune to Stern-Gerlach-type experiments. Recently, however, it has been suggested that graphene pseudospin is a real angular momentum that might manifest itself as an observable quantity, but so far direct tests of such a momentum remained unfruitful. Here, by selective excitation of two sublattices of an artificial photonic graphene, we demonstrate pseudospin-mediated vortex generation and topological charge flipping in otherwise uniform optical beams with Bloch momentum traversing through the Dirac points. Corroborated by numerical solutions of the linear massless Dirac-Weyl equation, we show that pseudospin can turn into orbital angular momentum completely, thus upholding the belief that pseudospin is not merely for theoretical elegance but rather physically measurable.
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Duca L, Li T, Reitter M, Bloch I, Schleier-Smith M, Schneider U. An Aharonov-Bohm interferometer for determining Bloch band topology. Science 2014; 347:288-92. [DOI: 10.1126/science.1259052] [Citation(s) in RCA: 185] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Komesu T, Le D, Ma Q, Schwier EF, Kojima Y, Zheng M, Iwasawa H, Shimada K, Taniguchi M, Bartels L, Rahman TS, Dowben PA. Symmetry-resolved surface-derived electronic structure of MoS2(0 0 0 1). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:455501. [PMID: 25301782 DOI: 10.1088/0953-8984/26/45/455501] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We find a wave vector dependence of the band symmetries for MoS(2)(0 0 0 1) in angle-resolved photoemission. The band structures are found to be significantly different for states of even and odd reflection parities, despite the absence of true mirror plane symmetry away from Γ, the Brillouin zone center, along the line to the K point, at the Brillouin zone edge. Our measurements agree with density functional theory (DFT) calculations for each band symmetry, with the notable exception of the Mo 4d(x(2)-y(2)) contributions to the valence band structure of MoS(2)(0 0 0 1). The band structure is indicative of strong S 3p and Mo 4d hybridization. In particular, the top of the valence band is predominantly composed of Mo 4d(3z(2)-r(2)) derived states near Γ, whereas near K Mo 4d(x(2)-y(2)) as well as Mo 4d(xy) dominate. In contrast, the bottom of the valence band is dominated by Mo 5s and S 3p(z) contributions.
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Affiliation(s)
- Takashi Komesu
- Department of Physics and Astronomy, Theodore Jorgensen Hall, 855 N 16th, University of Nebraska, Lincoln, NE 68588-0299, USA
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Hwang C. Angle-resolved photoemission spectroscopy study on graphene using circularly polarized light. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:335501. [PMID: 25056276 DOI: 10.1088/0953-8984/26/33/335501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We have investigated graphene using circularly polarized light via angle-resolved photoemission spectroscopy. We observe that photoelectron intensity rotates around a constant energy contour towards the opposite direction upon changing the chirality of light. Interestingly, the circular dichroism is found to be asymmetric with respect to the Dirac energy, which is not explained by the Berry phase effect (Liu et al 2011 Phys. Rev. Lett. 107 166803). We also report that the energy spectra taken using the light with different chiralities show a finite separation from each other. We discuss possible origins of the unusual circular dichroism observed in graphene.
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Affiliation(s)
- Choongyu Hwang
- Department of Physics, Pusan National University, Busan 609-735, Korea
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Laboratory-based real and reciprocal space imaging of the electronic structure of few layer graphene on SiC(0001¯) using photoelectron emission microscopy. Ultramicroscopy 2013; 130:94-100. [PMID: 23541462 DOI: 10.1016/j.ultramic.2013.02.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 02/03/2013] [Accepted: 02/05/2013] [Indexed: 11/24/2022]
Abstract
We present real and reciprocal space photoelectron emission microscopy (PEEM) results on few layer graphene using laboratory based He I and II radiation. The combination of a focused high-intensity source and high transmission PEEM electron optics provides good signal to noise ratios for the different modes of acquisition. We demonstrate work function mapping and secondary electron analysis, related to the graphene layer thickness, band structure imaging from micron scale regions by wave vector resolved PEEM (k-PEEM) and local secondary electron spectroscopy, giving information on the valence and conduction band states and the dispersion relations of the π bands. Dark field PEEM is done by selecting the Dirac cone corresponding to the specific rotation of each graphene layer and allows spatial mapping of the commensurate rotation angles. The use of He II radiation increases the volume of reciprocal space accessible to k-PEEM and improves signal to background. The preferential linear polarization of the light source is used to investigate aspects of the electronic chirality near the Dirac cone. Recent developments in sample manipulation and cooling are presented.
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Weiss NO, Zhou H, Liao L, Liu Y, Jiang S, Huang Y, Duan X. Graphene: an emerging electronic material. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2012; 24:5782-825. [PMID: 22930422 DOI: 10.1002/adma.201201482] [Citation(s) in RCA: 168] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 06/14/2012] [Indexed: 05/06/2023]
Abstract
Graphene, a single layer of carbon atoms in a honeycomb lattice, offers a number of fundamentally superior qualities that make it a promising material for a wide range of applications, particularly in electronic devices. Its unique form factor and exceptional physical properties have the potential to enable an entirely new generation of technologies beyond the limits of conventional materials. The extraordinarily high carrier mobility and saturation velocity can enable a fast switching speed for radio-frequency analog circuits. Unadulterated graphene is a semi-metal, incapable of a true off-state, which typically precludes its applications in digital logic electronics without bandgap engineering. The versatility of graphene-based devices goes beyond conventional transistor circuits and includes flexible and transparent electronics, optoelectronics, sensors, electromechanical systems, and energy technologies. Many challenges remain before this relatively new material becomes commercially viable, but laboratory prototypes have already shown the numerous advantages and novel functionality that graphene provides.
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Affiliation(s)
- Nathan O Weiss
- Department of Materials Science and Engineering, UCLA, Los Angeles, CA 90095, USA
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Gierz I, Lindroos M, Höchst H, Ast CR, Kern K. Graphene sublattice symmetry and isospin determined by circular dichroism in angle-resolved photoemission spectroscopy. NANO LETTERS 2012; 12:3900-3904. [PMID: 22784029 DOI: 10.1021/nl300512q] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The Dirac-like electronic structure of graphene originates from the equivalence of the two basis atoms in the honeycomb lattice. We show that the characteristic parameters of the initial state wave function (sublattice symmetry and isospin) can be determined using angle-resolved photoemission spectroscopy (ARPES) with circularly polarized synchrotron radiation. At a photon energy of hν = 52 eV, transition matrix element effects can be neglected allowing us to determine sublattice symmetry and isospin with high accuracy using a simple theoretical model.
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Affiliation(s)
- Isabella Gierz
- Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
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Barrett N, Conrad E, Winkler K, Krömker B. Dark field photoelectron emission microscopy of micron scale few layer graphene. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:083706. [PMID: 22938302 DOI: 10.1063/1.4746279] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We demonstrate dark field imaging in photoelectron emission microscopy (PEEM) of heterogeneous few layer graphene (FLG) furnace grown on SiC(000-1). Energy-filtered, threshold PEEM is used to locate distinct zones of FLG graphene. In each region, selected by a field aperture, the k-space information is imaged using appropriate transfer optics. By selecting the photoelectron intensity at a given wave vector and using the inverse transfer optics, dark field PEEM gives a spatial distribution of the angular photoelectron emission. In the results presented here, the wave vector coordinates of the Dirac cones characteristic of commensurate rotations of FLG on SiC(000-1) are selected providing a map of the commensurate rotations across the surface. This special type of contrast is therefore a method to map the spatial distribution of the local band structure and offers a new laboratory tool for the characterisation of technically relevant, microscopically structured matter.
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Affiliation(s)
- N Barrett
- IRAMIS/SPCSI/LENSIS, F-91191 Gif-sur-Yvette, France.
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Bian G, Zhang L, Liu Y, Miller T, Chiang TC. Illuminating the surface spin texture of the giant-Rashba quantum-well system Bi/Ag(111) by circularly polarized photoemission. PHYSICAL REVIEW LETTERS 2012; 108:186403. [PMID: 22681094 DOI: 10.1103/physrevlett.108.186403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Indexed: 06/01/2023]
Abstract
We have mapped out the spin texture of a Bi/Ag surface alloy prepared on a thin Ag film by circularly polarized angle-resolved photoemission spectroscopy. A term proportional to ∇·A in the interaction Hamiltonian gives rise to strong surface photoexcitation, which interferes with a Rashba contribution to yield a pronounced circular dichroic effect in Bi/Ag. The dipole transition, often taken to be the only important photoexcitation mechanism, is actually negligible. A parameter-free calculation yields a dichroic pattern in excellent agreement with experiment.
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Affiliation(s)
- Guang Bian
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA
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Park SR, Han J, Kim C, Koh YY, Kim C, Lee H, Choi HJ, Han JH, Lee KD, Hur NJ, Arita M, Shimada K, Namatame H, Taniguchi M. Chiral orbital-angular momentum in the surface states of Bi2Se3. PHYSICAL REVIEW LETTERS 2012; 108:046805. [PMID: 22400876 DOI: 10.1103/physrevlett.108.046805] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Indexed: 05/31/2023]
Abstract
We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi2Se3. We observed circular dichroism (CD) as large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs in CD. The observed CD is attributed to the existence of local orbital-angular momentum (OAM). First-principles calculation shows that OAM in the surface states is significant and is locked to the electron momentum in the opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility for strong light-induced spin-polarized current in surface states. We also provide a proof for local OAM origin of the CD in ARPES.
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Affiliation(s)
- Seung Ryong Park
- Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Korea
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