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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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Gati E, Fischer JKH, Lunkenheimer P, Zielke D, Köhler S, Kolb F, von Nidda HAK, Winter SM, Schubert H, Schlueter JA, Jeschke HO, Valentí R, Lang M. Evidence for Electronically Driven Ferroelectricity in a Strongly Correlated Dimerized BEDT-TTF Molecular Conductor. PHYSICAL REVIEW LETTERS 2018; 120:247601. [PMID: 29957011 DOI: 10.1103/physrevlett.120.247601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Indexed: 06/08/2023]
Abstract
By applying measurements of the dielectric constants and relative length changes to the dimerized molecular conductor κ-(BEDT-TTF)_{2}Hg(SCN)_{2}Cl, we provide evidence for order-disorder type electronic ferroelectricity that is driven by the charge order within the (BEDT-TTF)_{2} dimers and stabilized by a coupling to the anions. According to our density functional theory calculations, this material is characterized by a moderate strength of dimerization. This system thus bridges the gap between strongly dimerized materials, often approximated as dimer-Mott systems at 1/2 filling, and nondimerized or weakly dimerized systems at 1/4 filling, exhibiting a charge order. Our results indicate that intradimer charge degrees of freedom are of particular importance in correlated κ-(BEDT-TTF)_{2}X salts and can create novel states, such as electronically driven multiferroicity or charge-order-induced quasi-one-dimensional spin liquids.
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Affiliation(s)
- Elena Gati
- Institute of Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - Jonas K H Fischer
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Peter Lunkenheimer
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - David Zielke
- Institute of Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - Sebastian Köhler
- Institute of Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - Felizitas Kolb
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Hans-Albrecht Krug von Nidda
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Stephen M Winter
- Institute for Theoretical Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - Harald Schubert
- Institute of Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - John A Schlueter
- Division of Materials Research, National Science Foundation, Arlington, Virginia 22230, USA
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - Harald O Jeschke
- Institute for Theoretical Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
- Research Institute for Interdisciplinary Science, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan
| | - Roser Valentí
- Institute for Theoretical Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
| | - Michael Lang
- Institute of Physics, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany
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Structural and Electronic Properties of (TMTTF)2X Salts with Tetrahedral Anions. CRYSTALS 2018. [DOI: 10.3390/cryst8030121] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Light-Induced Current Oscillations in the Charge-Ordered State of (TMTTF)2SbF6. CRYSTALS 2017. [DOI: 10.3390/cryst7090278] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Below T CO = 157 K the quasi-one-dimensional charge-transfer salt (TMTTF) 2 SbF 6 undergoes a pronounced phase transition to a charge-ordered ground state. We have explored the non-linear and photoconductive behavior as a function of applied voltage, laser pulse energy and temperature. Besides a decay of the photoconductive signal in a double exponential fashion in the millisecond range, we discover current oscillations in the kHz range induced by the application of short laser pulses. While the resonance frequencies do not depend on voltage or laser intensity and vary only slightly with temperature, the amplitude changes linearly with the laser intensity and voltage. We suggest that photo-induced fluctuations of the charge-ordered state alter the current flow of the single particles and hence, the photocurrent. The findings are discussed and compared to comparable phenomena in other low-dimensional electron systems.
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Infrared Investigations of the Neutral-Ionic Phase Transition in TTF-CA and Its Dynamics. CRYSTALS 2017. [DOI: 10.3390/cryst7010017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Liu D, Ishikawa K, Takehara R, Miyagawa K, Tamura M, Kanoda K. Insulating Nature of Strongly Correlated Massless Dirac Fermions in an Organic Crystal. PHYSICAL REVIEW LETTERS 2016; 116:226401. [PMID: 27314731 DOI: 10.1103/physrevlett.116.226401] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Indexed: 06/06/2023]
Abstract
Through resistivity measurements of an organic crystal hosting massless Dirac fermions with a charge-ordering instability, we reveal the effect of interactions among massless Dirac fermions on the charge transport. A low-temperature resistivity upturn appears robustly irrespective of the pressure and is enhanced while approaching the critical pressure of charge ordering, indicating that the insulating behavior originates from short-range Coulomb interactions. The observation of an apparently vanishing gap in the charge-ordered phase accords with the theoretical prediction of nontopological edge states.
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Affiliation(s)
- Dong Liu
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Kyohei Ishikawa
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Ryosuke Takehara
- 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
| | - Kazushi Kanoda
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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Lunkenheimer P, Loidl A. Dielectric spectroscopy on organic charge-transfer salts. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:373001. [PMID: 26325011 DOI: 10.1088/0953-8984/27/37/373001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
This topical review provides an overview of the dielectric properties of a variety of organic charge-transfer salts, based on both, data reported in literature and our own experimental results. Moreover, we discuss in detail the different processes that can contribute to the dielectric response of these materials. We concentrate on the family of the 1D (TMTTF)2 X systems and the 2D BEDT-TTF-based charge-transfer salts, which in recent years have attracted considerable interest due to their often intriguing dielectric properties. We will mainly focus on the occurrence of electronic ferroelectricity in these systems, which also includes examples of multiferroicity.
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Affiliation(s)
- P Lunkenheimer
- Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
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Optical freezing of charge motion in an organic conductor. Nat Commun 2014; 5:5528. [DOI: 10.1038/ncomms6528] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 10/09/2014] [Indexed: 11/08/2022] Open
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Ito A, Nakamura Y, Nakamura A, Kishida H. Measurement of the nonlinear conducting states of α-(BEDT-TTF)2I3 using electronic Raman scattering. PHYSICAL REVIEW LETTERS 2013; 111:197801. [PMID: 24266489 DOI: 10.1103/physrevlett.111.197801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Revised: 04/22/2013] [Indexed: 06/02/2023]
Abstract
Nonlinear conducting states in a strongly correlated organic electronic system α-(BEDT-TTF)2I3 [BEDT-TTF=bis(ethylenedithio)-tetrathiafulvalene] are studied by Raman spectroscopy. Wide-range Raman spectra of nonlinear conducing states provide direct information about conducting properties through the electronic Raman process. A comparison between the behaviors of the electronic modes of BEDT-TTF layers and the vibrational mode of I3 molecules reveals the formation of nonequilibrium states in which only the electronic parts show the change of states. We obtained a spatial map of the conducting regions of the nonlinear conducting states by utilizing the electronic Raman intensity as a measure of the highly conducting states. A spatially inhomogeneous formation of nonlinear conducting states was observed.
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Affiliation(s)
- Atsuya Ito
- Department of Applied Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
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Tomić S, Pinterić M, Ivek T, Sedlmeier K, Beyer R, Wu D, Schlueter JA, Schweitzer D, Dressel M. Magnetic ordering and charge dynamics in κ-(BEDT-TTF)2Cu[N(CN)2]Cl. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2013; 25:436004. [PMID: 24107640 DOI: 10.1088/0953-8984/25/43/436004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl consists of molecular dimers arranged on an anisotropic triangular lattice. At low temperatures a pronounced dielectric anomaly is observed, and eventually a canted antiferromagnetic ground state forms. Optical spectroscopy clearly rules out charge imbalance and the existence of quantum electric dipoles with a dipolar-spin coupling. Here we suggest a novel form of spin-charge coupling where the prominent in-plane dielectric response in κ-(BEDT-TTF)2Cu[N(CN)2]Cl is explained by short-range discommensurations of the antiferromagnetic phase in the temperature range 30 K < T < 50 K, and by relaxation of charged domain walls in the ferromagnetic structure at lower temperatures.
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Affiliation(s)
- S Tomić
- Institut za fiziku, PO Box 304, HR-10001 Zagreb, Croatia
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Itoh K, Itoh H, Naka M, Saito S, Hosako I, Yoneyama N, Ishihara S, Sasaki T, Iwai S. Collective excitation of an electric dipole on a molecular dimer in an organic dimer-Mott insulator. PHYSICAL REVIEW LETTERS 2013; 110:106401. [PMID: 23521274 DOI: 10.1103/physrevlett.110.106401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Revised: 12/21/2012] [Indexed: 06/01/2023]
Abstract
The terahertz response in 10-100 cm(-1) was investigated in an organic dimer-Mott (DM) insulator κ-(ET)(2)Cu(2)(CN)(3) that exhibits a relaxorlike dielectric anomaly. An ~30 cm(-1) band in the optical conductivity was attributable to collective excitation of the fluctuating intradimer electric dipoles that are formed by an electron correlation. We succeeded in observing photoinduced enhancement of this ~30 cm(-1) band, reflecting the growth of the electric dipole cluster in the DM phase. Such optical responses in κ-(ET)(2)Cu(2)(CN)(3) reflect an instability near the boundary between the DM-ferroelectric charge ordered phases.
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Affiliation(s)
- K Itoh
- Department of Physics, Tohoku University, Sendai 980-8578, Japan
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Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands. CRYSTALS 2012. [DOI: 10.3390/cryst2031291] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Photoinduced Phase Transitions in α-, θ-, and κ-type ET Salts: Ultrafast Melting of the Electronic Ordering. CRYSTALS 2012. [DOI: 10.3390/cryst2020590] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Dressel M. Quantum criticality in organic conductors? Fermi liquid versus non-Fermi-liquid behaviour. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:293201. [PMID: 21727309 DOI: 10.1088/0953-8984/23/29/293201] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Organic metals exhibit unusual electronic properties in their charge and spin degrees of freedom that have puzzled physicists for decades. By now this behaviour is established as intrinsic and related to electronic interactions. Like other correlated electron systems, such as heavy fermions or transition-metal oxides, organic conductors are located next to some ordered phase in the spin or charge sectors. Theory predicts quantum fluctuations to become important at low temperatures and quantum critical behaviour present in most physical properties. Here we survey the experimental evidence of quantum criticality in well-established organic model compounds and look for indications of non-Fermi-liquid behaviour.
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Affiliation(s)
- Martin Dressel
- Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, Stuttgart, Germany
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