"Pudding Mold"-type Band as an Origin of Large Thermopower in tau-type Organic Conductors

TL;DR

This paper investigates the large thermopower in a tau-type organic conductor, attributing it to a unique 'pudding mold'-type band structure through ab initio calculations and Boltzmann transport theory.

Contribution

It demonstrates that the 'pudding mold'-type band structure is responsible for the large Seebeck coefficient in the studied organic conductor.

Findings

Large thermopower is linked to the pudding mold band structure.

Maximum Seebeck coefficient occurs at a specific temperature.

Band structure calculations match experimental thermopower trends.

Abstract

We study the origin of the large thermopower in quasi-two-dimensional a $\tau$-type organic conductor, $\tau-(EDO-S,S-DMEDT-TTF)_2(AuBr_2)_{1+y}$ ($y \le 0.875$), from the view point of a "pudding mold"-type band structure. We calculate the electronic band structure using an \textit{ab initio} band calculation package, and obtain a tight binding model fit to the \textit{ab initio} band structure. Using the model and the Boltzmann's equation approach, we calculate the temperature dependence of the Seebeck coefficient. We conclude that the peculiar band structure is the origin of the large Seebeck coefficient and the appearance of the maximum value at a certain temperature.