Colossal Seebeck coefficient of hopping electrons in (TMTSF)$_{2}$PF$_{6}$

TL;DR

This study reveals that in (TMTSF)$_{2}$PF$_{6}$, hopping electrons in the low-temperature VRH regime produce an exceptionally large Seebeck coefficient, confirming a long-standing theoretical prediction about Coulomb interactions.

Contribution

It provides the first experimental evidence that Coulomb-interacting hopping electrons can generate a colossal Seebeck coefficient at near-zero temperatures.

Findings

Seebeck coefficient reaches 400 $k_{B}$/$e$ in the VRH regime

Hopping electrons contribute significantly to thermoelectric response

Results confirm theoretical predictions about Coulomb interactions in hopping conduction

Abstract

We report on a study of Seebeck coefficient and resistivity in the quasi-one-dimensional conductor (TMTSF)$_{2}$PF$_{6}$ extended deep into the Spin-Density-Wave(SDW) state. The metal-insulator transition at $T_{SDW}$ = 12 K leads to a reduction in carrier concentration by seven orders of magnitude. Below 1 K, charge transport displays the behavior known as Variable Range Hopping (VRH). Until now, the Seebeck response of electrons in this regime has been barely explored and even less understood. We find that in this system, residual carriers, hopping from one trap to another, generate a Seebeck coefficient as large as 400 $k_{B}$/$e$. The results provide the first solid evidence for a long-standing prediction according to which hopping electrons in presence of Coulomb interaction can generate a sizeable Seebeck coefficient in the zero-temperature limit.