Unusual size effects on thermoelectricity in a strongly correlated oxide

TL;DR

This study reveals that in strongly correlated layered cobaltate thin films, thermopower remains unaffected by size down to 6 nm, contrasting with conventional theories, and highlights unique size-dependent thermoelectric behaviors.

Contribution

The paper demonstrates that strong electron correlations lead to size-independent thermopower in thin films, challenging traditional models and providing new understanding of thermoelectric properties in correlated materials.

Findings

Thermopower is independent of thickness down to 6 nm.

Resistivity increases below approximately 30 nm thickness.

Thermoelectric behavior differs from uncorrelated systems under size effects.

Abstract

We investigated size effects on thermoelectricity in thin films of a strongly correlated layered cobaltate. At room temperature, the thermopower is independent of thickness down to 6 nm. This unusual behavior is inconsistent with the Fuchs-Sondheimer theory, which is used to describe conventional metals and semiconductors, and is attributed to the strong electron correlations in this material. Although the resistivity increases, as expected, below a critical thickness of $\sim$ 30 nm. The temperature dependent thermopower is similar for different thicknesses but resistivity shows systematic changes with thickness. Our experiments highlight the differences in thermoelectric behavior of strongly correlated and uncorrelated systems when subjected to finite size effects. We use the atomic limit Hubbard model at the high temperature limit to explain our observations. These findings provide new insights on decoupling electrical conductivity and thermopower in correlated systems.