Thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator $\beta'$-(BEDT-TTF)$_2$ICl$_2$

TL;DR

This study investigates the thermoelectric properties of a low-dimensional organic insulator, revealing anomalously large thermopower and unusual transport relations linked to its quasi-one-dimensional structure.

Contribution

It provides new insights into thermoelectric behavior of low-dimensional organic materials, highlighting the role of anisotropic molecular orbitals in enhancing thermopower.

Findings

Thermopower shows activation-type temperature dependence with anomalously large values.

Unusual relation between thermopower and resistivity observed in Jonker-plot analysis.

Low dimensionality contributes to enhanced thermoelectric properties.

Abstract

Low-dimensional materials, in which the electronic and transport properties are drastically modified in comparison to those of three-dimensional bulk materials, yield a key class of thermoelectric materials with high conversion efficiency. Among such materials, the organic compounds may serve peculiar properties owing to their unique molecular-based low-dimensional structures with highly anisotropic molecular orbitals. Here we present the thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator $\beta'$-(BEDT-TTF)$_2$ICl$_2$, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. We find that the thermopower exhibits typical activation-type temperature variation expected for insulators but its absolute value is anomalously large compared to the expected value from the activation-type temperature dependence of the electrical resistivity. Successively, the Jonker-plot analysis, in which the thermopower is usually scaled by the logarithm of the resistivity, shows an unusual relation among such transport quantities. We discuss a role of the low dimensionality for the enhanced thermopower along with recent observations of such a large thermopower in several low-dimensional materials.