Large Seebeck coefficient driven by "pudding mold" flat band in hole-doped CuRhO$_2$

TL;DR

This study reveals that the large Seebeck coefficient in hole-doped CuRhO$_2$ is due to a flat band edge near the Fermi level, demonstrating the potential of flat band oxides for thermoelectric energy conversion.

Contribution

It provides direct experimental evidence of a pudding mold band structure in CuRhO$_2$ and links this to its high thermoelectric performance, supported by theoretical calculations.

Findings

Identification of pudding mold band structure in CuRhO$_2$

Seebeck coefficient of ~200 μV/K consistent with calculations

Flat band edges in oxides as a route for efficient thermoelectricity

Abstract

We report the measurement, using angle-resolved photoemission spectroscopy, of the metallic electronic structure of the hole-doped thermoelectric oxide CuRh$_{0.9}$Mg$_{0.1}$O$_2$. The material is found to have a ``pudding mold'' type band structure, with a nearly flat band edge located near the Fermi level, which is thought to be the origin of the thermoelectric behavior of this material. The experimental data match the density functional theory of the undoped parent compound, simply corrected by a rigid shift of the bands. Transport calculations based on the observed band structure yield a Seebeck coefficient of $\sim 200 \,\mu$V/K for the undoped parent material, consistent with experimental measurements. Our results show that CuRhO$_2$ is a textbook example of how pure band-structural effects can result in a large thermoelectric figure of merit, demonstrating that flat band edges in oxides are a realistic route for the efficient conversion of thermal energy.