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Abstract
This short review article provides the reader with a summary of the history of organic conductors. To retain a neutral and objective point of view regarding the history, background, novelty, and details of each research subject within this field, a thousand references have been cited with full titles and arranged in chronological order. Among the research conducted over ~70 years, topics from the last two decades are discussed in more detail than the rest. Unlike other papers in this issue, this review will help readers to understand the origin of each topic within the field of organic conductors and how they have evolved. Due to the advancements achieved over these 70 years, the field is nearing new horizons. As history is often a reflection of the future, this review is expected to show the future directions of this research field.
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Revelli Beaumont M, Hemme P, Gallais Y, Sacuto A, Jacob K, Valade L, de Caro D, Faulmann C, Cazayous M. Possible observation of the signature of the bad metal phase and its crossover to a Fermi liquid in κ-(BEDT-TTF) 2Cu(NCS) 2 bulk and nanoparticles by Raman scattering. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:125403. [PMID: 33463531 DOI: 10.1088/1361-648x/abd813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
κ-(BEDT-TTF)2Cu(NCS)2 has been investigated by Raman scattering in both bulk and nanoparticle compounds. Phonon modes from 20 to 1600 cm-1 have been assigned. Focusing on the unexplored low frequency phonons, a plateau in frequencies is observed in the bulk phonons between 50 and 100 K and assigned to the signature of the bad metal phase. Nanoparticles of κ-(BEDT-TTF)2Cu(NCS)2 exhibit anomalies at 50 K associated to the crossover from a bad metal to a Fermi liquid whose origins are discussed.
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Affiliation(s)
- M Revelli Beaumont
- Laboratoire Matériaux et Phénomènes Quantiques (UMR 7162 CNRS), Université de Paris, 75205 Paris Cedex 13, France. Laboratoire de Chimie de Coordination (UPR 8241), Université Paul Sabatier Toulouse, France
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3
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Dressel M, Pustogow A. Electrodynamics of quantum spin liquids. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:203001. [PMID: 29692367 DOI: 10.1088/1361-648x/aabc1f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Quantum spin liquids attract great interest due to their exceptional magnetic properties characterized by the absence of long-range order down to low temperatures despite the strong magnetic interaction. Commonly, these compounds are strongly correlated electron systems, and their electrodynamic response is governed by the Mott gap in the excitation spectrum. Here we summarize and discuss the optical properties of several two-dimensional quantum spin liquid candidates. First we consider the inorganic material herbertsmithite ZnCu3(OH)6Cl2 and related compounds, which crystallize in a kagome lattice. Then we turn to the organic compounds [Formula: see text]-EtMe3Sb[Pd(dmit)2]2, κ-(BEDT-TTF)2Ag2(CN)3 and κ-(BEDT-TTF)2Cu2(CN)3, where the spins are arranged in an almost perfect triangular lattice, leading to strong frustration. Due to differences in bandwidth, the effective correlation strength varies over a wide range, leading to a rather distinct behavior as far as the electrodynamic properties are concerned. We discuss the spinon contributions to the optical conductivity in comparison to metallic quantum fluctuations in the vicinity of the Mott transition.
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Affiliation(s)
- Martin Dressel
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
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Raman Scattering as a Probe of the Magnetic State of BEDT-TTF Based Mott Insulators. CRYSTALS 2018. [DOI: 10.3390/cryst8060233] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Barman H, Laad MS, Hassan SR. Can disorder act as a chemical pressure? An optical study of the Hubbard model. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:195603. [PMID: 29595521 DOI: 10.1088/1361-648x/aabaa1] [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
The optical properties have been studied using the dynamical mean-field theory on a disordered Hubbard model. Despite the fact that disorder turns a metal to an insulator in high dimensional correlated materials, we notice that it can enhance certain metallic behavior as if a chemical pressure is applied to the system resulting in an increase of the effective lattice bandwidth (BW). We study optical properties in such a scenario and compare results with experiments where the BW is changed through isovalent chemical substitution (keeping electron filling unaltered) and obtain remarkable similarities vindicating our claim. We also make the point that these similarities differ from some other forms of BW tuned optical effects.
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Affiliation(s)
- H Barman
- Institute of Mathematical Sciences, Taramani, Chennai 600113, India
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Powell BJ, Kenny EP, Merino J. Dynamical Reduction of the Dimensionality of Exchange Interactions and the "Spin-Liquid" Phase of κ-(BEDT-TTF)_{2}X. PHYSICAL REVIEW LETTERS 2017; 119:087204. [PMID: 28952764 DOI: 10.1103/physrevlett.119.087204] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Indexed: 06/07/2023]
Abstract
We show that the anisotropy of the effective spin model for the dimer Mott insulator phase of κ-(BEDT-TTF)_{2}X salts is dramatically different from that of the underlying tight-binding model. Intradimer quantum interference results in a model of coupled spin chains, where frustrated interchain interactions suppress long-range magnetic order. Thus, we argue, the "spin liquid" phase observed in some of these materials is a remnant of the Tomonaga-Luttinger physics of a single chain. This is consistent with previous experiments and resolves some outstanding puzzles.
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Affiliation(s)
- B J Powell
- School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - E P Kenny
- School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - J Merino
- Departamento de Física Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Madrid 28049, Spain
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7
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Li W, Rose E, Tran MV, Hübner R, Łapiński A, Świetlik R, Torunova SA, Zhilyaeva EI, Lyubovskaya RN, Dressel M. The metal-insulator transition in the organic conductor β ″-(BEDT-TTF) 2Hg(SCN) 2Cl. J Chem Phys 2017; 147:064503. [PMID: 28810750 DOI: 10.1063/1.4997198] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We explore the nature of the metal-insulator transition in the two-dimensional organic compound β″-(BEDT-TTF)2Hg(SCN)2Cl by x-ray, electrical transport, ESR, Raman, and infrared investigations. Magnetic and vibrational spectroscopy concurrently reveal a gradual dimerization along the stacking direction (a-b), setting in already at the crossover temperature of 150 K from the metallic to the insulating state. A spin gap of Δσ=47 meV is extracted. From the activated resistivity behavior below T = 55 K, a charge gap of Δρ=60 meV is derived. At TCO = 72 K, the C=C vibrational modes reveal the development of a charge-ordered state with a charge disproportionation of 2δρ=0.34e. In addition to a slight structural dimerization, charge-order causes stripes most likely perpendicular to the stacks.
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Affiliation(s)
- Weiwu Li
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Eva Rose
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Minh Vu Tran
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Ralph Hübner
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
| | - Andrzej Łapiński
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland
| | - Roman Świetlik
- Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland
| | - Svetlana A Torunova
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142 432 Chernogolovka, Russia
| | - Elena I Zhilyaeva
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142 432 Chernogolovka, Russia
| | - Rimma N Lyubovskaya
- Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142 432 Chernogolovka, Russia
| | - Martin Dressel
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany
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Tie M, Dhirani AA. Electrolyte-gated charge transport in molecularly linked gold nanoparticle films: The transition from a Mott insulator to an exotic metal with strong electron-electron interactions. J Chem Phys 2016; 145:104702. [DOI: 10.1063/1.4962342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
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Merino J, Gunnarsson O, Kotliar G. Self-energy behavior away from the Fermi surface in doped Mott insulators. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:045501. [PMID: 26742570 DOI: 10.1088/0953-8984/28/4/045501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.
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Affiliation(s)
- J Merino
- Departamento de Física Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC) and Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, Madrid 28049, Spain
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Diehl S, Methfessel T, Tutsch U, Müller J, Lang M, Huth M, Jourdan M, Elmers HJ. Disorder-induced gap in the normal density of states of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:265601. [PMID: 26076168 DOI: 10.1088/0953-8984/27/26/265601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The local density of states (DOS) of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br, measured by scanning tunneling spectroscopy on in situ cleaved surfaces, reveals a logarithmic suppression near the Fermi edge persisting above the critical temperature T(c). The experimentally observed suppression of the DOS is in excellent agreement with a soft Hubbard gap as predicted by the Anderson-Hubbard model for systems with disorder. The electronic disorder also explains the diminished coherence peaks of the quasi-particle DOS below T(c).
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Affiliation(s)
- Sandra Diehl
- Graduate School Materials Science In Mainz, Staudingerweg 9, 55128 Mainz, Germany. Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany
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Xu W, Haule K, Kotliar G. Hidden Fermi liquid, scattering rate saturation, and Nernst effect: a dynamical mean-field theory perspective. PHYSICAL REVIEW LETTERS 2013; 111:036401. [PMID: 23909344 DOI: 10.1103/physrevlett.111.036401] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Indexed: 06/02/2023]
Abstract
We investigate the transport properties of a correlated metal within dynamical mean-field theory. Canonical Fermi liquid behavior emerges only below a very low temperature scale T(FL). Surprisingly the quasiparticle scattering rate follows a quadratic temperature dependence up to much higher temperatures and crosses over to saturated behavior around a temperature scale T(sat). We identify these quasiparticles as constituents of the hidden Fermi liquid. The non-Fermi-liquid transport above T(FL), in particular the linear-in-T resistivity, is shown to be a result of a strongly temperature dependent band dispersion. We derive simple expressions for the resistivity, Hall angle, thermoelectric power and Nernst coefficient in terms of a temperature dependent renormalized band structure and the quasiparticle scattering rate. We discuss possible tests of the dynamical mean-field theory picture of transport using ac measurements.
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Affiliation(s)
- Wenhu Xu
- Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, New Jersey 08854, USA
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Kokalj J, McKenzie RH. Thermodynamics of a bad metal-Mott insulator transition in the presence of frustration. PHYSICAL REVIEW LETTERS 2013; 110:206402. [PMID: 25167433 DOI: 10.1103/physrevlett.110.206402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Indexed: 06/03/2023]
Abstract
Thermodynamic properties of the Hubbard model on the anisotropic triangular lattice at half filling are calculated by the finite-temperature Lanczos method. The charge susceptibility exhibits clear signatures of a Mott metal-insulator transition. The metallic phase is characterized by a small charge susceptibility, large entropy, large renormalized quasiparticle mass, and large spin susceptibility. The fluctuating local magnetic moment in the metallic phase is large and comparable to that in the insulating phase. These bad metallic characteristics occur above a relatively low coherence temperature, as seen in organic charge transfer salts.
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Affiliation(s)
- J Kokalj
- School of Mathematics and Physics, University of Queensland, Brisbane, 4072 Queensland, Australia
| | - Ross H McKenzie
- School of Mathematics and Physics, University of Queensland, Brisbane, 4072 Queensland, Australia
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Deng X, Mravlje J, Zitko R, Ferrero M, Kotliar G, Georges A. How bad metals turn good: spectroscopic signatures of resilient quasiparticles. PHYSICAL REVIEW LETTERS 2013; 110:086401. [PMID: 23473178 DOI: 10.1103/physrevlett.110.086401] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Indexed: 06/01/2023]
Abstract
We investigate transport in strongly correlated metals. Within dynamical mean-field theory, we calculate the resistivity, thermopower, optical conductivity and thermodynamic properties of a hole-doped Mott insulator. Two well-separated temperature scales are identified: T(FL) below which Landau Fermi liquid behavior applies, and T(MIR) above which the resistivity exceeds the Mott-Ioffe-Regel value and bad-metal behavior is found. We show that quasiparticle excitations remain well defined above T(FL) and dominate transport throughout the intermediate regime T(FL) </~ T </~ T(MIR). The lifetime of these resilient quasiparticles is longer for electronlike excitations and this pronounced particle-hole asymmetry has important consequences for the thermopower. The crossover into the bad-metal regime corresponds to the disappearance of these excitations and has clear signatures in optical spectroscopy.
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Affiliation(s)
- Xiaoyu Deng
- Centre de Physique Théorique, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex, France
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Mott-Anderson Transition in Molecular Conductors: Influence of Randomness on Strongly Correlated Electrons in the κ-(BEDT-TTF)2X System. CRYSTALS 2012. [DOI: 10.3390/cryst2020374] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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15
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Toda Y, Mertelj T, Naito T, Mihailovic D. Femtosecond carrier relaxation dynamics and photoinduced phase separation in κ-(BEDT-TTF)2Cu[N(CN)2]X (X=Br,Cl). PHYSICAL REVIEW LETTERS 2011; 107:227002. [PMID: 22182038 DOI: 10.1103/physrevlett.107.227002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Indexed: 05/31/2023]
Abstract
We investigate the relaxation dynamics of nonequilibrium carriers in organic conductors κ-(BEDT-TTF)(2)Cu[N(CN)(2)]X (X=Br and Cl) using ultrafast time-resolved optical spectroscopy. The dynamics for both salts show similar temperature dependences, which is well characterized by the carrier relaxation across the pseudogap (PG) of the magnitude Δ(PG) ≈ 16 meV for Br salt and 7.0 meV for Cl salt. On the other hand, only the Br salt shows an abrupt increase of the decay time at low temperature, indicating an additional decay component associated with the superconducting (SC) gap below T(c). The fluence dependent dynamics at low temperature evidences the superposition of the SC component onto the PG component. These results indicate a metallic-insulating phase separation in the Br salt triggered by photoexcited nonequilibrium carriers.
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Affiliation(s)
- Y Toda
- Complex Matter Department, Jozef Stefan Institute, Jamova 39, Ljubljana, SI-1000, Slovenia
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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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Sasaki T, Yoneyama N, Nakamura Y, Kobayashi N, Ikemoto Y, Moriwaki T, Kimura H. Optical probe of carrier doping by X-ray irradiation in the organic dimer Mott insulator kappa-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl. PHYSICAL REVIEW LETTERS 2008; 101:206403. [PMID: 19113361 DOI: 10.1103/physrevlett.101.206403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2008] [Indexed: 05/27/2023]
Abstract
We investigated the infrared optical spectra of an organic dimer Mott insulator kappa-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Cl, which was irradiated with x rays. We observed that the irradiation caused a large spectral weight transfer from the midinfrared region, where interband transitions in the dimer and Mott-Hubbard bands take place, to a Drude part in a low-energy region; this caused the Mott gap to collapse. The increase of the Drude part indicates a carrier doping into the Mott insulator due to irradiation defects. The strong redistribution of the spectral weight demonstrates that the organic Mott insulator is very close to the phase border of the bandwidth-controlled Mott-insulator-metal transition.
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Affiliation(s)
- T Sasaki
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
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