Seebeck Coefficient of Two-dimensional Dirac Electrons in Organic Conductor under Pressure

TL;DR

This study investigates the temperature-dependent Seebeck coefficient of Dirac electrons in an organic conductor under pressure, revealing sign changes explained by spectral conductivity and comparing results with experimental data.

Contribution

It provides a theoretical analysis of the Seebeck coefficient's anomalous temperature dependence in a 2D Dirac electron system under pressure, incorporating impurity and electron-phonon scatterings.

Findings

Seebeck coefficient shows sign change with temperature.

Maximum and minimum of S occur at high and low temperatures.

Theoretical results agree with experimental observations.

Abstract

The Seebeck coefficient, which is proportional to a ratio of the thermoelectric conductivity to electrical conductivity has been examined for Dirac electrons in the organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$ [BEDT-TTF denotes a molecule given by bis(ethylenedithio)tetrathiafulvalene] under a uniaxial pressure using a two-dimensional tight-binding model with both impurity and electron--phonon (e--p) scatterings. We calculate an anomalous temperature ($T$) dependence of the Seebeck coefficient $S_{\nu}$ with $\nu = x$ (perpendicular to the molecular stacking axis) and $y$, which shows $S_\nu > 0$ with a maximum at high temperatures and $S_{\nu} < 0$ with a minimum at low temperatures.The microscopic mechanism of such a sign change of $S_\nu$ is clarified in terms of the spectral conductivity. The result is compared with experiments on $\alpha$-(BEDT-TTF)$_2$I$_3$.