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Lu X, Zhang S, Wang Y, Gao X, Yang K, Guo Z, Gao Y, Ye Y, Han Z, Liu J. Synergistic correlated states and nontrivial topology in coupled graphene-insulator heterostructures. Nat Commun 2023; 14:5550. [PMID: 37689704 PMCID: PMC10492827 DOI: 10.1038/s41467-023-41293-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Accepted: 08/29/2023] [Indexed: 09/11/2023] Open
Abstract
Graphene has aroused great attention due to the intriguing properties associated with its low-energy Dirac Hamiltonian. When graphene is coupled with a correlated insulating substrate, electronic states that cannot be revealed in either individual layer may emerge in a synergistic manner. Here, we theoretically study the correlated and topological states in Coulomb-coupled and gate-tunable graphene-insulator heterostructures. By electrostatically aligning the electronic bands, charge carriers transferred between graphene and the insulator can yield a long-wavelength electronic crystal at the interface, exerting a superlattice Coulomb potential on graphene and generating topologically nontrivial subbands. This coupling can further boost electron-electron interaction effects in graphene, leading to a spontaneous bandgap formation at the Dirac point and interaction-enhanced Fermi velocity. Reciprocally, the electronic crystal at the interface is substantially stabilized with the help of cooperative interlayer Coulomb coupling. We propose a number of substrate candidates for graphene to experimentally demonstrate these effects.
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Affiliation(s)
- Xin Lu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China
| | - Shihao Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China
| | - Yaning Wang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
| | - Xiang Gao
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, 030006, Taiyuan, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006, Taiyuan, China
| | - Kaining Yang
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, 030006, Taiyuan, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006, Taiyuan, China
| | - Zhongqing Guo
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China
| | - Yuchen Gao
- Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing, 100871, China
| | - Yu Ye
- Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China
- State Key Lab for Mesoscopic Physics and Frontiers Science Center for Nano-Optoelectronics, School of Physics, Peking University, Beijing, 100871, China
| | - Zheng Han
- State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, 030006, Taiyuan, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, 030006, Taiyuan, China
| | - Jianpeng Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai, 201210, China.
- ShanghaiTech Laboratory for Topological Physics, ShanghaiTech University, Shanghai, 201210, China.
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Kirby RJ, Scholes GD, Schoop LM. Square-Net Topological Semimetals: How Spectroscopy Furthers Understanding and Control. J Phys Chem Lett 2022; 13:838-850. [PMID: 35044779 DOI: 10.1021/acs.jpclett.1c03798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Square-net materials are well positioned to lead optical spectroscopic explorations into the electronic structure, photoinduced dynamics, and phase transitions in topological semimetals. Hundreds of square-net topological semimetals can be prepared that have remarkably different electronic and optical properties despite having similar structures. Here we present what has been gleaned recently from these materials with the whole gamut of optical spectroscopies, ranging from steady-state reflectance and Raman investigations into topological band structures, electronic correlations, and equilibrium phase transitions to time-resolved techniques used to decipher ultrafast relaxation dynamics and nonequilibrium photoinduced phase transitions. We end with a discussion of some major remaining questions and possible future research directions.
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Affiliation(s)
- Robert J Kirby
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Gregory D Scholes
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Leslie M Schoop
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
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3
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Sonntag J, Reichardt S, Beschoten B, Stampfer C. Electrical Control over Phonon Polarization in Strained Graphene. NANO LETTERS 2021; 21:2898-2904. [PMID: 33797265 DOI: 10.1021/acs.nanolett.0c05043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We explore the tunability of the phonon polarization in suspended uniaxially strained graphene by magneto-phonon resonances. The uniaxial strain lifts the degeneracy of the LO and TO phonons, yielding two cross-linearly polarized phonon modes and a splitting of the Raman G peak. We utilize the strong electron-phonon coupling in graphene and the off-resonant coupling to a magneto-phonon resonance to induce a gate-tunable circular phonon dichroism. This, together with the strain-induced splitting of the G peak, allows us to controllably tune the two linearly polarized G mode phonons into circular phonon modes. We are able to achieve a circular phonon polarization of up to 40% purely by electrostatic fields and can reverse its sign by tuning from electron to hole doping. This provides unprecedented electrostatic control over the angular momentum of phonons, which paves the way toward phononic applications.
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Affiliation(s)
- Jens Sonntag
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Sven Reichardt
- Department of Physics and Materials Science, University of Luxembourg, L-1511 Luxembourg, Luxembourg
| | - Bernd Beschoten
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
| | - Christoph Stampfer
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany
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Hirata M, Kobayashi A, Berthier C, Kanoda K. Interacting chiral electrons at the 2D Dirac points: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2021; 84:036502. [PMID: 33059346 DOI: 10.1088/1361-6633/abc17c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 10/15/2020] [Indexed: 06/11/2023]
Abstract
The pseudo-relativistic chiral electrons in 2D graphene and 3D topological semimetals, known as the massless Dirac or Weyl fermions, constitute various intriguing issues in modern condensed-matter physics. In particular, the issues linked to the Coulomb interaction between the chiral electrons attract great attentions due to their unusual features, namely, the interaction is not screened and has a long-ranged property near the charge-neutrality point, in clear contrast to its screened and short-ranged properties in the conventional correlated materials. In graphene, this long-range interaction induces an anomalous logarithmic renormalization of the Fermi velocity, which causes a nonlinear reshaping of its Dirac cone. In addition, for strong interactions, it even leads to the predictions of an excitonic condensation with a spontaneous mass generation. The interaction, however, would seem to be not that large in graphene, so that the latter phenomenon appears to have not yet been observed. Contrastingly, the interaction is probably large in the pressurized organic materialα-(BEDT-TTF)2I3, where a 2D massless-Dirac-fermion phase emerges next to a correlated insulating phase. Therefore, an excellent testing ground would appear in this material for the studies of both the velocity renormalization and the mass generation, as well as for those of the short-range electronic correlations. In this review, we give an overview of the recent progress on the understanding of such interacting chiral electrons in 2D, by placing particular emphasis on the studies in graphene andα-(BEDT-TTF)2I3. In the first half, we briefly summarize our current experimental and theoretical knowledge about the interaction effects in graphene, then turn attentions to the understanding inα-(BEDT-TTF)2I3, and highlight its relevance to and difference from graphene. The second half of this review focusses on the studies linked to the nuclear magnetic resonance experiments and the associated model calculations inα-(BEDT-TTF)2I3. These studies allow us to discuss the anisotropic reshaping of a tilted Dirac cone together with various electronic correlations, and the precursor excitonic dynamics growing prior to a condensation. We see these provide unique opportunities to resolve the momentum dependence of the spin excitations and fluctuations that are strongly influenced by the long-range interaction near the Dirac points.
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Affiliation(s)
- Michihiro Hirata
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan
- MPA-Q, Los Alamos National Laboratory, NM 87545, United States of America
| | - Akito Kobayashi
- Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Claude Berthier
- Laboratoire National des Champs Magnétiques Intenses, UPR 3228 CNRS, EMFL, UGA, UPS and INSA, Boite Postale 166, 38042 Grenoble Cedex 9, France
| | - Kazushi Kanoda
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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Manipulating electronic structure of graphene for producing ferromagnetic graphene particles by Leidenfrost effect-based method. Sci Rep 2020; 10:6874. [PMID: 32327678 PMCID: PMC7181710 DOI: 10.1038/s41598-020-63478-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 04/01/2020] [Indexed: 11/30/2022] Open
Abstract
First isolation of graphene, as a great achievement, opens a new horizon in a broad range of science. Graphene is one of the most promising materials for spintronic fields whose application is limited due to its weak magnetic property. Despite many experimental and theoretical efforts for obtaining ferromagnetic graphene, still, a high degree of magnetization is an unsolved challenge. Even, in most observations, graphene magnetization is reported at extremely low temperatures rather than room temperature. In principle, the magnetic property of graphene is created by manipulation of its electronic structure. Removing or adding bonds of graphene such as creating vacancy defects, doping, adatom, edges, and functionalization can change the electronic structure and the external perturbation, such as external magnetic field, temperature, and strain can either. Recently, single and few-layer graphene have been investigated in the presence of these perturbations, and also the electronic changes have been determined by Raman spectroscopy. Here, we successfully could develop a simple and novel Leidenfrost effect-based method for graphene magnetization at room temperature with the external perturbations which apply simultaneously in the graphene flakes inside the Leidenfrost droplets. Macroscale ferromagnetic graphene particles are produced by this method. Briefly, the graphene is obtained by the liquid-phase exfoliation method in the ethanol solution media and also evaporates on the hot surface as a Leidenfrost droplet in the magnetic fields. Then, the floated graphene flakes circulate inside the droplets. Due to the strain and temperature inside the droplets and external magnetic field (the magnet in heater-stirrer), the electronic structure of graphene is instantly changed. The changes are extremely rapid that the graphene flakes behave as a charged particle and also produce an internal magnetic field during their circulation. The internal magnetic field is measured by sensors. As the main accomplishment of this study, we could develop a simple method for inducing magnetism obtained 0.4 emu/g in the graphene, as magnetization saturation at room temperature, which is higher than the reported values. Another achievement of this work is the detection of the Leidenfrost droplets magnetic field, as an internal one which has obtained for the first time. To investigate magnetic graphene particles, the magnetization process, and the electronic structure of the vibrating sample magnetometer (VSM), magnetic field sensor, and Raman spectroscopy are used, respectively.
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Molas MR, Slobodeniuk AO, Nogajewski K, Bartos M, Bala Ł, Babiński A, Watanabe K, Taniguchi T, Faugeras C, Potemski M. Energy Spectrum of Two-Dimensional Excitons in a Nonuniform Dielectric Medium. PHYSICAL REVIEW LETTERS 2019; 123:136801. [PMID: 31697524 DOI: 10.1103/physrevlett.123.136801] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Indexed: 06/10/2023]
Abstract
We demonstrate that, in monolayers (MLs) of semiconducting transition metal dichalcogenides, the s-type Rydberg series of excitonic states follows a simple energy ladder: ε_{n}=-Ry^{*}/(n+δ)^{2}, n=1,2,…, in which Ry^{*} is very close to the Rydberg energy scaled by the dielectric constant of the medium surrounding the ML and by the reduced effective electron-hole mass, whereas the ML polarizability is accounted for only by δ. This is justified by the analysis of experimental data on excitonic resonances, as extracted from magneto-optical measurements of a high-quality WSe_{2} ML encapsulated in hexagonal boron nitride (hBN), and well reproduced with an analytically solvable Schrödinger equation when approximating the electron-hole potential in the form of a modified Kratzer potential. Applying our convention to other MoSe_{2}, WS_{2}, MoS_{2} MLs encapsulated in hBN, we estimate an apparent magnitude of δ for each of the studied structures. Intriguingly, δ is found to be close to zero for WSe_{2} as well as for MoS_{2} monolayers, what implies that the energy ladder of excitonic states in these two-dimensional structures resembles that of Rydberg states of a three-dimensional hydrogen atom.
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Affiliation(s)
- M R Molas
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - A O Slobodeniuk
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
| | - K Nogajewski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - M Bartos
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Central European Institute of Technology, Brno University of Technology, Purkyňova 656/123, 61200 Brno, Czech Republic
| | - Ł Bala
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - A Babiński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - C Faugeras
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
| | - M Potemski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
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Nedoliuk IO, Hu S, Geim AK, Kuzmenko AB. Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material. NATURE NANOTECHNOLOGY 2019; 14:756-761. [PMID: 31285609 DOI: 10.1038/s41565-019-0489-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Accepted: 05/30/2019] [Indexed: 06/09/2023]
Abstract
When two-dimensional electron gases (2DEGs) are exposed to a magnetic field, they resonantly absorb electromagnetic radiation via electronic transitions between Landau levels1. In 2DEGs with a Dirac spectrum, such as graphene, theory predicts an exceptionally high infrared magneto-absorption, even at zero doping2-5. However, the measured Landau-level magneto-optical effects in graphene have been much weaker than expected2,6-12 because of imperfections in the samples available for such experiments. Here, we measure magneto-transmission and Faraday rotation in high-mobility encapsulated monolayer graphene using a custom-designed set-up for magneto-infrared microspectroscopy. Our results show strongly enhanced magneto-optical activity in the infrared and terahertz ranges, characterized by absorption of light near to the 50% maximum allowed, 100% magnetic circular dichroism and high Faraday rotation. Considering that sizeable effects have been already observed at routinely achievable magnetic fields, our findings demonstrate the potential of magnetic tuning in 2D Dirac materials for long-wavelength optoelectronics and plasmonics.
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Affiliation(s)
| | - Sheng Hu
- School of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Andre K Geim
- School of Physics and Astronomy, University of Manchester, Manchester, UK
- National Graphene Institute, University of Manchester, Manchester, UK
| | - Alexey B Kuzmenko
- Department of Quantum Matter Physics, University of Geneva, Geneva, Switzerland.
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8
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Yin LJ, Shi LJ, Li SY, Zhang Y, Guo ZH, He L. High-Magnetic-Field Tunneling Spectra of ABC-Stacked Trilayer Graphene on Graphite. PHYSICAL REVIEW LETTERS 2019; 122:146802. [PMID: 31050464 DOI: 10.1103/physrevlett.122.146802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2018] [Indexed: 06/09/2023]
Abstract
ABC-stacked trilayer graphene (TLG) was predicted to exhibit novel many-body phenomena due to the existence of almost dispersionless flat bands near the charge neutrality point. Here, using high-magnetic-field scanning tunneling microscopy, we present Landau Level (LL) spectroscopy measurements of high-quality ABC-stacked TLG on graphite. We observe an approximately linear magnetic-field scaling of valley splitting and spin splitting in the ABC-stacked TLG. Our experiment indicates that the spin splitting decreases dramatically with increasing the LL index. When the lowest LL is partially filled, we find an obvious enhancement of the spin splitting, attributing to strong many-body effects. Moreover, we observe linear energy scaling of the inverse lifetime of quasiparticles, providing an additional evidence for the strong electron-electron interactions in the ABC-stacked TLG. These results imply that interesting broken-symmetry states and novel electron correlated effects could emerge in the ABC-stacked TLG in the presence of high magnetic fields.
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Affiliation(s)
- Long-Jing Yin
- Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing, 100875, China
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha, 410082, China
| | - Li-Juan Shi
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha, 410082, China
| | - Si-Yu Li
- Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Yu Zhang
- Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Zi-Han Guo
- Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing, 100875, China
| | - Lin He
- Center for Advanced Quantum Studies, Department of Physics, Beijing Normal University, Beijing, 100875, China
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9
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Cong X, Wu JB, Lin ML, Liu XL, Shi W, Venezuela P, Tan PH. Stokes and anti-Stokes Raman scattering in mono- and bilayer graphene. NANOSCALE 2018; 10:16138-16144. [PMID: 30117506 DOI: 10.1039/c8nr04554b] [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
Stokes and anti-Stokes Raman spectroscopy associated with the intervalley double resonance process in carbon materials is a unique technique to reveal the relationship between their characteristic electronic band structures and phonon dispersion. In graphene, the dominant resonant behavior for its 2D mode is an intervalley triple resonance Raman process. In this paper, we report the Stokes and anti-Stokes Raman scattering of the 2D mode in pristine graphene. The excitation energy (Eex)-dependent frequency discrepancy between anti-Stokes and Stokes components of the 2D mode (Δω(2D)) is observed, which is in good agreement with the theoretical results. This is attributed to the nonlinear dispersion of the in-plane transverse optical (iTO) phonon branch near the K point, confirmed by the nonlinear Eex-dependent frequency of the 2D mode (ω(2D)) in the range of 1.58-3.81 eV. The wavevector-dependent phonon group velocity of the iTO phonon branch is directly derived from Δω(2D). The Stokes and anti-Stokes Raman scattering of the D mode in defected graphene and the 2D mode in bilayer graphene associated with intervalley double resonance Raman processes is also reported.
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Affiliation(s)
- Xin Cong
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
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Tang HK, Leaw JN, Rodrigues JNB, Herbut IF, Sengupta P, Assaad FF, Adam S. The role of electron-electron interactions in two-dimensional Dirac fermions. Science 2018; 361:570-574. [DOI: 10.1126/science.aao2934] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Accepted: 05/25/2018] [Indexed: 11/02/2022]
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Sonntag J, Reichardt S, Wirtz L, Beschoten B, Katsnelson MI, Libisch F, Stampfer C. Impact of Many-Body Effects on Landau Levels in Graphene. PHYSICAL REVIEW LETTERS 2018; 120:187701. [PMID: 29775369 DOI: 10.1103/physrevlett.120.187701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Indexed: 06/08/2023]
Abstract
We present magneto-Raman spectroscopy measurements on suspended graphene to investigate the charge carrier density-dependent electron-electron interaction in the presence of Landau levels. Utilizing gate-tunable magnetophonon resonances, we extract the charge carrier density dependence of the Landau level transition energies and the associated effective Fermi velocity v_{F}. In contrast to the logarithmic divergence of v_{F} at zero magnetic field, we find a piecewise linear scaling of v_{F} as a function of the charge carrier density, due to a magnetic-field-induced suppression of the long-range Coulomb interaction. We quantitatively confirm our experimental findings by performing tight-binding calculations on the level of the Hartree-Fock approximation, which also allow us to estimate an excitonic binding energy of ≈6 meV contained in the experimentally extracted Landau level transitions energies.
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Affiliation(s)
- J Sonntag
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany
| | - S Reichardt
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
- Physics and Materials Science Research Unit, University of Luxembourg, L-1511 Luxembourg, Luxembourg
| | - L Wirtz
- Physics and Materials Science Research Unit, University of Luxembourg, L-1511 Luxembourg, Luxembourg
| | - B Beschoten
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
| | - M I Katsnelson
- Institute for Molecules and Materials, Radboud University, 6525AJ Nijmegen, Netherlands
| | - F Libisch
- Institute for Theoretical Physics, Vienna University of Technology, 1040 Vienna, Austria
| | - C Stampfer
- JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany
- Peter Grünberg Institute (PGI-9), Forschungszentrum Jülich, 52425 Jülich, Germany
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12
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Yumoto G, Matsunaga R, Hibino H, Shimano R. Ultrafast Terahertz Nonlinear Optics of Landau Level Transitions in a Monolayer Graphene. PHYSICAL REVIEW LETTERS 2018; 120:107401. [PMID: 29570346 DOI: 10.1103/physrevlett.120.107401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2017] [Indexed: 06/08/2023]
Abstract
We investigated the ultrafast terahertz (THz) nonlinearity in a monolayer graphene under the strong magnetic field using THz pump-THz probe spectroscopy. An ultrafast suppression of the Faraday rotation associated with inter-Landau level (LL) transitions is observed, reflecting the Dirac electron character of nonequidistant LLs with large transition dipole moments. A drastic modulation of electron distribution in LLs is induced by far off-resonant THz pulse excitation in the transparent region. Numerical simulation based on the density matrix formalism without rotating-wave approximation reproduces the experimental results. Our results indicate that the strong light-matter coupling regime is realized in graphene, with the Rabi frequency exceeding the carrier wave frequency and even the relevant energy scale of the inter-LL transition.
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Affiliation(s)
- Go Yumoto
- Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
| | - Ryusuke Matsunaga
- Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
| | - Hiroki Hibino
- School of Science and Technology, Kwansei Gakuin University, Hyogo 669-1337, Japan
- NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporation, Kanagawa 243-0198, Japan
| | - Ryo Shimano
- Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
- Cryogenic Research Center, The University of Tokyo, Tokyo 113-0032, Japan
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Russell BJ, Zhou B, Taniguchi T, Watanabe K, Henriksen EA. Many-Particle Effects in the Cyclotron Resonance of Encapsulated Monolayer Graphene. PHYSICAL REVIEW LETTERS 2018; 120:047401. [PMID: 29437433 DOI: 10.1103/physrevlett.120.047401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 11/12/2017] [Indexed: 06/08/2023]
Abstract
We study the infrared cyclotron resonance of high-mobility monolayer graphene encapsulated in hexagonal boron nitride, and simultaneously observe several narrow resonance lines due to interband Landau-level transitions. By holding the magnetic field strength B constant while tuning the carrier density n, we find the transition energies show a pronounced nonmonotonic dependence on the Landau-level filling factor, ν∝n/B. This constitutes direct evidence that electron-electron interactions contribute to the Landau-level transition energies in graphene, beyond the single-particle picture. Additionally, a splitting occurs in transitions to or from the lowest Landau level, which is interpreted as a Dirac mass arising from coupling of the graphene and boron nitride lattices.
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Affiliation(s)
- B Jordan Russell
- Department of Physics, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, USA
| | - Boyi Zhou
- Department of Physics, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, USA
| | - T Taniguchi
- National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0044, Japan
| | - K Watanabe
- National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0044, Japan
| | - Erik A Henriksen
- Department of Physics, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, USA
- Institute for Materials Science and Engineering, Washington University in St. Louis, 1 Brookings Drive, St. Louis, Missouri 63130, USA
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14
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Downing CA, Portnoi ME. Bielectron vortices in two-dimensional Dirac semimetals. Nat Commun 2017; 8:897. [PMID: 29026126 PMCID: PMC5638912 DOI: 10.1038/s41467-017-00949-y] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 08/08/2017] [Indexed: 11/12/2022] Open
Abstract
Searching for new states of matter and unusual quasi-particles in emerging materials and especially low-dimensional systems is one of the major trends in contemporary condensed matter physics. Dirac materials, which host quasi-particles which are described by ultrarelativistic Dirac-like equations, are of a significant current interest from both a fundamental and applied physics perspective. Here we show that a pair of two-dimensional massless Dirac–Weyl fermions can form a bound state independently of the sign of the inter-particle interaction potential, as long as this potential decays at large distances faster than Kepler’s inverse distance law. This leads to the emergence of a new type of energetically favorable quasiparticle: bielectron vortices, which are double-charged and reside at zero-energy. Their bosonic nature allows for condensation and may give rise to Majorana physics without invoking a superconductor. These novel quasi-particles arguably explain a range of poorly understood experiments in gated graphene structures at low doping. Two-dimensional Dirac semimetals are known to host fermionic excitations which can mimic physics usually found in ultrarelativistic quantum mechanics. Here, the authors unveil the existence of another type of quasiparticle, bielectron vortices, which are bosonic and may give rise to new types of condensates.
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Affiliation(s)
- C A Downing
- Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, Strasbourg, F-67000, France. .,School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK.
| | - M E Portnoi
- School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK. .,International Institute of Physics, Universidade Federal do Rio Grande do Norte, Natal-RN, 59078-970, Brazil.
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15
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Stauber T, Parida P, Trushin M, Ulybyshev MV, Boyda DL, Schliemann J. Interacting Electrons in Graphene: Fermi Velocity Renormalization and Optical Response. PHYSICAL REVIEW LETTERS 2017; 118:266801. [PMID: 28707915 DOI: 10.1103/physrevlett.118.266801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Indexed: 06/07/2023]
Abstract
We have developed a Hartree-Fock theory for electrons on a honeycomb lattice aiming to solve a long-standing problem of the Fermi velocity renormalization in graphene. Our model employs no fitting parameters (like an unknown band cutoff) but relies on a topological invariant (crystal structure function) that makes the Hartree-Fock sublattice spinor independent of the electron-electron interaction. Agreement with the experimental data is obtained assuming static self-screening including local field effects. As an application of the model, we derive an explicit expression for the optical conductivity and discuss the renormalization of the Drude weight. The optical conductivity is also obtained via precise quantum Monte Carlo calculations which compares well to our mean-field approach.
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Affiliation(s)
- T Stauber
- Departamento de Teoría y Simulación de Materiales, Instituto de Ciencia de Materiales de Madrid, CSIC, E-28049 Madrid, Spain
| | - P Parida
- Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - M Trushin
- Department of Physics, University of Konstanz, D-78457 Konstanz, Germany
| | - M V Ulybyshev
- Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
| | - D L Boyda
- Far Eastern Federal University, Sukhanova 8, Vladivostok 690950, Russia
- ITEP, B. Cheremushkinskaya 25, Moscow 117218, Russia
| | - J Schliemann
- Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany
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16
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Zhang CX, Qiu XG. Optical signatures of parity anomaly in a gapped graphene-like system. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:205701. [PMID: 28322214 DOI: 10.1088/1361-648x/aa6804] [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
Parity anomaly refers to the violation of coordinate reflection symmetry induced by the quantum fluctuations. It is proposed to exist in a graphene-like system with a finite bare mass for Dirac fermions, and manifests itself as a parity-violating quantum correction to the current of each species of fermions. Coulomb interaction greatly increases the fermion mass, and produces various types of excitons. Of particular interest is the ρ-exciton, which is directly connected to parity anomaly and can be generated by absorbing a specific photon. The exciton is a particle-hole bound state, and can be regarded as condensed-matter analogue of meson composed of quark-anti-quark pair. By virtue of this correspondence, we analyze the optical conductivity and calculate the mass of ρ-exciton by employing the Shifman-Vainshtein-Zakharov sum rule method that is widely used in the studies of hadron phenomenology. We show that ρ-exciton leads to a sharp peak in the optical conductivity, which is observable in optical experiments. Moreover, we study the impact of scalar-like excitons on two-photon processes by computing the decay amplitude, and also find peaks in the Raman spectra.
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Affiliation(s)
- C X Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, People's Republic of China
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17
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Hirata M, Ishikawa K, Miyagawa K, Tamura M, Berthier C, Basko D, Kobayashi A, Matsuno G, Kanoda K. Observation of an anisotropic Dirac cone reshaping and ferrimagnetic spin polarization in an organic conductor. Nat Commun 2016; 7:12666. [PMID: 27578363 PMCID: PMC5013692 DOI: 10.1038/ncomms12666] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 07/21/2016] [Indexed: 11/27/2022] Open
Abstract
The Coulomb interaction among massless Dirac fermions in graphene is unscreened around the isotropic Dirac points, causing a logarithmic velocity renormalization and a cone reshaping. In less symmetric Dirac materials possessing anisotropic cones with tilted axes, the Coulomb interaction can provide still more exotic phenomena, which have not been experimentally unveiled yet. Here, using site-selective nuclear magnetic resonance, we find a non-uniform cone reshaping accompanied by a bandwidth reduction and an emergent ferrimagnetism in tilted Dirac cones that appear on the verge of charge ordering in an organic compound. Our theoretical analyses based on the renormalization-group approach and the Hubbard model show that these observations are the direct consequences of the long-range and short-range parts of the Coulomb interaction, respectively. The cone reshaping and the bandwidth renormalization, as well as the magnetic behaviour revealed here, can be ubiquitous and vital for many Dirac materials.
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Affiliation(s)
- Michihiro Hirata
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
- Laboratoire National des Champs Magnétiques Intenses, UPR 3228 CNRS, EMFL, UGA, UPS and INSA, Boite Postale 166, Grenoble, Cedex 9 38042, France
| | - Kyohei Ishikawa
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Kazuya Miyagawa
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Masafumi Tamura
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan
| | - Claude Berthier
- Laboratoire National des Champs Magnétiques Intenses, UPR 3228 CNRS, EMFL, UGA, UPS and INSA, Boite Postale 166, Grenoble, Cedex 9 38042, France
| | - Denis Basko
- Université Grenoble Alpes and CNRS, Laboratoire de Physique et Modélisation des Milieux Condensés UMR 5493, 25 rue des Martyrs, Grenoble 38042, France
| | - Akito Kobayashi
- Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Genki Matsuno
- Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
| | - Kazushi Kanoda
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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18
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Yang W, Lu X, Chen G, Wu S, Xie G, Cheng M, Wang D, Yang R, Shi D, Watanabe K, Taniguchi T, Voisin C, Plaçais B, Zhang Y, Zhang G. Hofstadter Butterfly and Many-Body Effects in Epitaxial Graphene Superlattice. NANO LETTERS 2016; 16:2387-2392. [PMID: 26950258 DOI: 10.1021/acs.nanolett.5b05161] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Graphene placed on hexagonal boron nitride (h-BN) has received a wide range of interest due to the improved electrical performance and rich physics from the interface, especially the emergence of superlattice Dirac points as well as Hofstadter butterfly in high magnetic field. Instead of transferring graphene onto h-BN, epitaxial growth of graphene directly on a single-crystal h-BN provides an alternative and promising way to study these interesting superlattice effects due to their precise lattice alignment. Here we report an electrical transport study on epitaxial graphene superlattice on h-BN with a period of ∼15.6 nm. The epitaxial graphene superlattice is clean, intrinsic, and of high quality with a carrier mobility of ∼27 000 cm(2) V(-1) s(-1), which enables the observation of Hofstadter butterfly features originated from the superlattice at a magnetic field as low as 6.4 T. A metal-insulator transition and magnetic field dependent Fermi velocity were also observed, suggesting prominent electron-electron interaction-induced many-body effects.
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Affiliation(s)
- Wei Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et Marie Curie-Sorbonne Universités, Université Paris Diderot-Sorbonne Paris Cité , 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Xiaobo Lu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Guorui Chen
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University , Shanghai 200433, China
| | - Shuang Wu
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Guibai Xie
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Meng Cheng
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Duoming Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Rong Yang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Dongxia Shi
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
| | - Kenji Watanabe
- Advanced Materials Laboratory, National Institute for Materials Science , 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Takashi Taniguchi
- Advanced Materials Laboratory, National Institute for Materials Science , 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Christophe Voisin
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et Marie Curie-Sorbonne Universités, Université Paris Diderot-Sorbonne Paris Cité , 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Bernard Plaçais
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et Marie Curie-Sorbonne Universités, Université Paris Diderot-Sorbonne Paris Cité , 24 rue Lhomond, 75231 Paris Cedex 05, France
| | - Yuanbo Zhang
- State Key Laboratory of Surface Physics and Department of Physics, Fudan University , Shanghai 200433, China
| | - Guangyu Zhang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China
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19
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Tonkikh AA, Voloshina EN, Werner P, Blumtritt H, Senkovskiy B, Güntherodt G, Parkin SSP, Dedkov YS. Structural and electronic properties of epitaxial multilayer h-BN on Ni(111) for spintronics applications. Sci Rep 2016; 6:23547. [PMID: 27009238 PMCID: PMC4806377 DOI: 10.1038/srep23547] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Accepted: 03/09/2016] [Indexed: 12/01/2022] Open
Abstract
Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to a large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and to close-packed surfaces of fcc-Ni(111) and hcp-Co(0001). Epitaxial deposition of h-BN on ferromagnetic metals is aimed at small interface scattering of charge and spin carriers. We report on the controlled growth of h-BN/Ni(111) by means of molecular beam epitaxy (MBE). Structural and electronic properties of this system are investigated using cross-section transmission electron microscopy (TEM) and electron spectroscopies which confirm good agreement with the properties of bulk h-BN. The latter are also corroborated by density functional theory (DFT) calculations, revealing that the first h-BN layer at the interface to Ni is metallic. Our investigations demonstrate that MBE is a promising, versatile alternative to both the exfoliation approach and chemical vapour deposition of h-BN.
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Affiliation(s)
- A A Tonkikh
- Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany.,Institute for Physics of Microstructures RAS, 603950, GSP-105, Nizhny Novgorod, Russia
| | - E N Voloshina
- Humboldt-Universität zu Berlin, Institut für Chemie, 10099 Berlin, Germany
| | - P Werner
- Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany
| | - H Blumtritt
- Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany
| | - B Senkovskiy
- Institute of Solid State Physics, Dresden University of Technology, 01062 Dresden, Germany.,St. Petersburg State University, 198504 St. Petersburg, Russia
| | - G Güntherodt
- Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany.,2nd Institute of Physics and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany
| | - S S P Parkin
- Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany
| | - Yu S Dedkov
- SPECS Surface Nano Analysis GmbH, Voltastraße 5, 13355 Berlin, Germany
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20
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Riccardi E, Méasson MA, Cazayous M, Sacuto A, Gallais Y. Gate-Dependent Electronic Raman Scattering in Graphene. PHYSICAL REVIEW LETTERS 2016; 116:066805. [PMID: 26919008 DOI: 10.1103/physrevlett.116.066805] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2015] [Indexed: 06/05/2023]
Abstract
We report the direct observation of polarization resolved electronic Raman scattering in a gated monolayer graphene device. The evolution of the electronic Raman scattering spectra with gate voltage and its polarization dependence are in full agreement with theoretical expectations for nonresonant Raman processes involving interband electron-hole excitations across the Dirac cone. We further show that the spectral dependence of the electronic Raman scattering signal can be simply described by the dynamical polarizability of graphene in the long wavelength limit. The possibility to directly observe Dirac fermion excitations in graphene opens the way to promising Raman investigations of electronic properties of graphene and other 2D crystals.
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Affiliation(s)
- E Riccardi
- Laboratoire Matériaux et Phénoménes Quantiques (UMR 7162 CNRS), Université Paris Diderot-Paris 7, Bâtiment Condorcet, 75205 Paris Cedex 13, France
| | - M-A Méasson
- Laboratoire Matériaux et Phénoménes Quantiques (UMR 7162 CNRS), Université Paris Diderot-Paris 7, Bâtiment Condorcet, 75205 Paris Cedex 13, France
| | - M Cazayous
- Laboratoire Matériaux et Phénoménes Quantiques (UMR 7162 CNRS), Université Paris Diderot-Paris 7, Bâtiment Condorcet, 75205 Paris Cedex 13, France
| | - A Sacuto
- Laboratoire Matériaux et Phénoménes Quantiques (UMR 7162 CNRS), Université Paris Diderot-Paris 7, Bâtiment Condorcet, 75205 Paris Cedex 13, France
| | - Y Gallais
- Laboratoire Matériaux et Phénoménes Quantiques (UMR 7162 CNRS), Université Paris Diderot-Paris 7, Bâtiment Condorcet, 75205 Paris Cedex 13, France
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21
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Sun C, Figge F, Ozfidan I, Korkusinski M, Yan X, Li LS, Hawrylak P, McGuire JA. Biexciton Binding of Dirac fermions Confined in Colloidal Graphene Quantum Dots. NANO LETTERS 2015; 15:5472-5476. [PMID: 26192636 DOI: 10.1021/acs.nanolett.5b01888] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We present transient absorption measurements and microscopic theory of biexciton binding in triangular colloidal graphene quantum dots consisting of 168 sp(2)-hybridized C atoms. We observe optical transitions from the lowest orbitally dark singlet exciton states to states below the energy of an unbound dark+bright singlet-exciton pair. Through microscopic calculations of the low-energy exciton and biexciton states via tight-binding, Hartree-Fock, and configuration interaction methods, the spectra reveal a biexciton consisting primarily of a dark-bright singlet-pair bound by ∼0.14 eV.
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Affiliation(s)
- Cheng Sun
- †Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - Florian Figge
- †Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - Isil Ozfidan
- §Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Marek Korkusinski
- ‡Quantum Theory Group, Security and Disruptive Technologies, Emerging Technologies Division, National Research Council of Canada, Ottawa, Ontario, K1A OR6 Canada
| | - Xin Yan
- ∥Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Liang-shi Li
- ∥Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Pawel Hawrylak
- §Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - John A McGuire
- †Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
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