Anomalous Thermoelectric Transport and Giant Nernst Effect in Multilayered Massless Dirac Fermion System

Konoike, T.; Sato, Munehiko; Uchida, K.; Osada, Toshiko

doi:10.7566/jpsj.82.073601

Cited by 34 publications

(35 citation statements)

References 26 publications

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“…39 Experimentally the existence of massless Dirac fermions has been concluded from various magneto-transport measurements, 27 from the NMR relaxation rate, 40,41 specific heat data 42 and the temperature dependence of the Nernst effect under pressure. 43 Recently evidence was presented that the high-mobility massless Dirac carriers coexist with lowmobility massive holes.…”

Section: 32-34mentioning

confidence: 99%

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: 32-34mentioning

confidence: 99%

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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“…The realization of a Dirac SM in α-(BEDT-TTF) 2 I 3 is experimentally suggested in indirect ways via negative interlayer magnetoresistance [12,13], interlayer Hall effect 3 [14,15], temperature dependence of magnetoresistance [16], specific heat [17], thermoelectric power [18], and site-selective NMR measurements [19,20]. Specifically, Ref.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy of Dirac cones and Van Hove singularity in an organic Dirac fermion system

et al. 2019

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We propose an experimental method to examine the in-plane anisotropy of electronic structure in layered conductors. In the method, we measure the interlayer magnetoresistance as a function of in-plane magnetic field orientation. We applied it to an organic Dirac fermion system α-(BEDT-TTF) 2 I 3 to experimentally determine the orientation of the anisotropic Dirac cones. It is concluded that the long axis of the elliptic constant-energy contours of the Dirac cone is tilted by approximately −30° from the crystalline a-axis to b-axis under hydrostatic pressures. Additionally, we observed a signature of van Hove singularity (which is a saddle point of the band dispersion) at 30-40 K above or below the Dirac point. The ridgeline of the saddle point is estimated as almost parallel to the crystalline b-axis.

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“…In this case, when the chemical potential is close to E N we can keep only the terms with n = N in the summation in Eqs. (14) and (15) which gives…”

Section: A High Magnetic Fieldsmentioning

confidence: 96%

“…(11) and (12) have matrix elements only for Landau levels with |n| = |m| ± 1, and the expressions for the conductivities in Eqs. (14) and (15) are considerably simplified. The conductivity becomes isotropic…”

Section: B Longitudinal Conductivitymentioning

confidence: 99%

“…9 The presence of relativistic Dirac quasiparticles in these materials gives rise to such interesting physical phenomena as unconventional quantum Hall effect, 2 crossover from the positive to negative interlayer magnetoresistance, 10,11 and giant Nernst-Ettingshausen effect. [12][13][14] Organic conductor α-(BEDT-TTF) 2 I 3 is a layered material which consists of conducting layers of BEDT-TTF molecules separated by insulating layers of I − 3 anions. Under the hydrostatic pressure about 1.5 GPa, it undergoes a transition to the zero-gap state with a typical ratio of the in-plane to the interlayer conductivity ∼ 10 3 which makes this compound a quasi-twodimensional conductor.…”

Section: Introductionmentioning

confidence: 99%

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Longitudinal conductivity of massless fermions with tilted Dirac cone in magnetic field

2015

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We investigate a longitudinal conductivity of a two-dimensional relativistic electron gas with a tilted Dirac cone in magnetic field. It is demonstrated that the conductivity behaves differently in the directions parallel and perpendicular to the tilting of the cone. At high magnetic fields, the conductivity at non-zero Landau levels in the direction perpendicular to the tilting modifies nontrivially, in contrast to the parallel case. At zero temperature, the crossover of the conductivity at the Dirac point from high to low magnetic field is studied numerically. It is found that the tilting produces anisotropy of the conductivity which changes with the magnetic field which is different from the anisotropy coming from the Fermi velocity. We also discuss the conductivity at finite temperatures and finite magnetic fields which can be directly compared with the experiments in α-(BEDT-TTF)2I3 organic conductor. We find that the tilting does not affect so much the magneticfield dependence of the conductivity except for the prefactor. We discuss the interpretation of recent experimental data and make some proposals to detect the effect of the tilting in future experiments.

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Anomalous Thermoelectric Transport and Giant Nernst Effect in Multilayered Massless Dirac Fermion System

Cited by 34 publications

References 26 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

Anisotropy of Dirac cones and Van Hove singularity in an organic Dirac fermion system

Longitudinal conductivity of massless fermions with tilted Dirac cone in magnetic field

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