Transport Phenomena in Multilayered Massless Dirac Fermion System α-(BEDT-TTF)2I3

Tajima, Naoya; Nishio, Y.; Kajita, Kôji

doi:10.3390/cryst2020643

Cited by 10 publications

(12 citation statements)

References 48 publications

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“…This might taken as an indication that the closing of the gap actually come to a halt with ∆ ≈ 16 meV. At a first glance this observation seems in contradiction to the metallic behavior reported from dc resistivity measurements; 13,23 however, we have to keep in mind that optical experiments only probe direct transitions (∆q = 0), 54 while temperature-dependent transport measures the smallest distance between two bands, i.e. indirect gaps.…”

Section: B Narrow-gap Regimementioning

confidence: 68%

“…At temperatures below the metal-insulator transition, transport and optical investigations 3,18,19 reveal the development of an energy gap that is also found in the band structure calculated by density functional theory, 10,20,21 as illustrated in port measurements 22,23 it was concluded that at high pressure α-(BEDT-TTF) 2 I 3 is best characterize as a semiconductor with an extremely narrow energy gap of less than 1 meV. Band structure calculations indicate that the bands actually touch each other at the Fermi energy, 10,20 supporting previous suggestions of Suzumura and collaborator.…”

Section: Introductionmentioning

confidence: 77%

“…Based on their semi-empirical investigations of the electronic structure, Katayama, Kobayashi, and Suzumura 25,26 suggested that a two-dimensional anisotropic Dirac cone dispersion occurs in α-(BEDT-TTF) 2 I 3 at high pressure, in analogy to the linear dispersion of the energy bands of graphene, although the situation is distinct as the states are not protected by topology, the Dirac cone is tilted and the zero-gap states can be tuned by pressure. 23,27 Very recently, Suzumura et al theoretically examined the dynamical conductivity of the massless electrons in the tilted Dirac cone, 74,75 i.e. with different velocities for the first and second band.…”

Section: Dirac Cone and Zero-gap Statementioning

confidence: 99%

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Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

et al. 2016

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Infrared optical investigations of α-(BEDT-TTF)2I3 have been performed in the spectral range from 80 to 8000 cm −1 down to temperatures as low as 10 K by applying hydrostatic pressure. In the metallic state, T > 135 K, we observe a 50% increase in the Drude contribution as well as the mid-infrared band due to the growing intermolecular orbital overlap with pressure up to 11 kbar. In the ordered state, T < TCO, we extract how the electronic charge per molecule varies with temperature and pressure: Transport and optical studies demonstrate that charge order and metalinsulator transition coincide and consistently yield a linear decrease of the transition temperature TCO by 8 − 9 K/kbar. The charge disproportionation ∆ρ diminishes by 0.017 e/kbar and the optical gap ∆ between the bands decreases with pressure by -47 cm −1 /kbar. In our high-pressure and low-temperature experiments, we do observe contributions from the massive charge carriers as well as from massless Dirac electrons to the low-frequency optical conductivity, however, without being able to disentangle them unambiguously.

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Section: B Narrow-gap Regimementioning

confidence: 68%

Section: Introductionmentioning

confidence: 77%

Section: Dirac Cone and Zero-gap Statementioning

confidence: 99%

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Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

et al. 2016

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“…For this reason, we anticipate an anomalous angular dependence of the spin susceptibility χ s and related NMR Knight shift for states close to k = q. These observations are extremely relevant, for example, to the α-phase Dirac semimetals α-(ET) 2 I 3 and α-(BETS) 2 I 3 [11][12][13][14]. Unlike graphene, the Dirac points in these materials are not symmetry protected; via Eq.…”

mentioning

confidence: 91%

“…The former material has been argued to form, under pressure, a zero gap semimetal (ZGS) with the Fermi energy located at the intersection of a pair of tilted Dirac cones [10,12,13]. However, the low-energy electronic and magnetic response shows significant departure from theoretical expectations for simple Dirac systems [14,15]. An unexplored aspect is the effect of spin-orbit coupling (SOC) in these systems.…”

mentioning

confidence: 99%

Importance of spin-orbit coupling in layered organic salts

2017

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We investigate the spin-orbit coupling (SOC) effects in α-and κ-phase BEDT-TTF and BEDT-TSF organic salts. Contrary to the assumption that SOC in organics is negligible due to light C, S, H atoms, we show the relevance of such an interaction in a few representative cases. In the weakly correlated regime, SOC manifests primarily in the opening of energy gaps at degenerate band touching points. This effect becomes especially important for Dirac semimetals such as α-(ET)2I3. Furthermore, in the magnetic insulating phase, SOC results in additional anisotropic exchange interactions, which provide a compelling explanation for the controversial field-induced behaviour of the quantum spin-liquid candidate κ-(ET)2Cu2(CN)3. We conclude by discussing the importance of SOC for the description of low-energy properties in organics.Layered organic materials have long served as ideal systems for studying complex physical phenomena such as the interplay between charge and spin order, unconventional superconductivity, and, exotic phases emerging from strong electronic correlations [1][2][3][4]. In these systems, high compressibility and synthetic versatility allows fine tuning of the underlying interactions via physical and chemical pressure, thus providing access to many different ground states. For example, significant evidence has recently emerged for a quantum spin liquid (QSL) state in a number of triangular-lattice organics,However, the appearance of very small energy gaps, and field-induced anomalies in the former material remain essentially unexplained. Likewise, interest has recently grown in the α-phase materials α-(ET) 2 I 3 [10] and α-(BETS) 2 I 3 [11]. The former material has been argued to form, under pressure, a zero gap semimetal (ZGS) with the Fermi energy located at the intersection of a pair of tilted Dirac cones [10,12,13]. However, the low-energy electronic and magnetic response shows significant departure from theoretical expectations for simple Dirac systems [14,15]. An unexplored aspect is the effect of spin-orbit coupling (SOC) in these systems.For (inorganic) magnetic insulators, strong SOC may generate large anisotropic magnetic interactions, associated with exotic spin-liquid states discussed e.g. for the iridates and α-RuCl 3 [16][17][18][19][20][21][22]. In weakly correlated systems such as BiSb, Bi 2 Te 3 , etc. [23][24][25][26], SOC tends to open a gap in the bulk, and may lead to nontrivial band topology and associated exotic edge states. Such effects have rarely been considered for the organic ET salts, as the light C, S, H atoms provide only moderate SOC. Nonetheless, it is known that SOC plays a dominant role in the spin relaxation of graphene [27][28][29] and organic-based semiconductors [30], and may be relatively enhanced for orbitally degenerate systems [31]. Indeed, in this work, we argue, despite a weak relative magnitude, that SOC is relevant for the low-energy properties in selected (representative) organic salts. We discuss as primary examples, the α-phase Dirac semimetals, and κ-phase...

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Electronic structure of the α-(BEDT-TTF)2I3 surface by photoelectron spectroscopy

et al. 2019

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We report anomalies observed in photoelectron spectroscopy measurements performed on α-(BEDT-TTF)2I3 crystals. In particular, above its metal-insulator transition temperature (T " 135 K), we observe the lack of a sharp Fermi edge in contradiction with the metallic transport properties exhibited by this quasi-bidimensional organic material. We interpret these unusual results as a signature of a one-dimensional electronic behavior confirmed by DFT band structure calculations. Using photoelectron spectroscopy we probe a Luttinger liquid with a large correlation parameter (α ą 1) that we interpret to be caused by the chain-like electronic structure of α-(BEDT-TTF)2I3 surface doped by iodine defects. These new surface effects are inaccessible by bulk sensitive measurements of electronic transport techniques.

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Transport Phenomena in Multilayered Massless Dirac Fermion System α-(BEDT-TTF)2I3

Cited by 10 publications

References 48 publications

Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

Importance of spin-orbit coupling in layered organic salts

Electronic structure of the α-(BEDT-TTF)2I3 surface by photoelectron spectroscopy

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