Universal thermopower of bad metals

TL;DR

This paper demonstrates that the simplified Hubbard model explains the universal thermopower behavior in bad metals across different doping levels, linking it to the chemical potential's temperature dependence and Kelvin formula applicability.

Contribution

It introduces a unified theoretical framework using the Hubbard model to understand the universal thermopower phenomena in bad metals near the Mott-Hubbard transition.

Findings

Universal thermopower behavior explained by Hubbard model

Chemical potential's temperature dependence is key

Kelvin formula accurately describes thermopower

Abstract

"Bad metals" have a large linear resistivity at high-T that is universally seen in oxides close to the Mott-Hubbard insulating phase. They also have an universal thermopower alpha(T): (i) at very low doping (lightly doped) alpha(T) has a pronounced low-T peak that shifts to higher-T with doping; (ii) at moderate doping (underdoped) alpha(T) has a small low-T peak that shifts to lower-T with doping and has a high-T sign change; and (iii) at the highest doping (overdoped) alpha(T) is negative and depends monotonically on T. Here we show that the simplified Hubbard model provides an easy to understand description of this phenomena due to the universal form for the chemical potential versus T for doped Mott insulators and the applicability of the Kelvin formula for the thermopower.