Anomalous conductivity of two-dimensional Dirac electrons in organic conductor under pressures

Abstract

Dirac electrons in organic conductor α-(BEDT-TTF)2I3 under pressures, which exhibit anomalous conductivity being nearly constant at high temperatures, have been examined using a two-dimensional tight-binding model (TB) model with both the impurity and electron-phonon (e-p) scatterings. A crucial role of scattering by acoustic phonon is shown based on the previous study for a model with simple Dirac cone [Phys. Rev. B 98,161205 (2018)]. In addition to diagonal conductivity σx = σxx and σy = σyy, off-diagonal conductivity σxy exists due to a tilted Dirac cone, where y (x) corresponds to a direction parallel (perpendicular) to a stacking axis of molecules. This σxy results in a rotation of axis of the principal value σ±. Since the conductivity at high temperatures is suppressed by the e-p scattering on the Dirac cone, the increase of temperature results in a broad maximum for σy and a nearly constant σx for a moderate choice of the e-p coupling constant. Further a correlation effect is examined employing a mean-field for the on-site and nearest-neighbor-site interactions. Anisotropic behavior of σν, (ν = x and y) is discussed by comparing with experiments of organic conductors, which present nearly constant resistivity at high temperatures.