Large Seebeck effect in the electron-doped FeAs$_2$ driven by quasi one dimensional pudding-mold type band

TL;DR

This study demonstrates a large Seebeck effect in electron-doped FeAs$_2$, attributed to a quasi-one-dimensional pudding-mold band structure, combining experimental measurements with theoretical band structure analysis.

Contribution

It identifies and explains the origin of the large Seebeck coefficient in doped FeAs$_2$ through combined experimental and theoretical approaches, highlighting the role of a pudding-mold type band.

Findings

Seebeck coefficient reaches -200 μV/K at 300 K for 1% doping

Quasi-one-dimensional pudding-mold band identified near the band gap

Theoretical calculations closely match experimental Seebeck values

Abstract

We investigate the thermoelectric propeties of the electron-doped FeAs$_2$ both experimentally and theoretically. Electrons are doped by partially substituting Se for As, which leads to a metallic behavior in the resistivity. A Seebeck coefficient of about $-$200 $\mu$V/K is reached at 300 K for 1% doping, and about $-$120 $\mu$V/K even at 5% doping. The origin of this large Seebeck coefficient despite the metallic conductivity is analyzed from a band structure point of view. The first-principles band calculation reveals the presence of a pudding-mold type band just above the band gap, somewhat similar to Na$_x$CoO$_2$, but with a quasi-one-dimensional nature. We calculate the Seebeck coefficient using a tightbinding model that correctly reproduces this band structure, and this gives results close to the experimental observations. The origin of this peculiar band shape is also discussed.