Specific-heat evidence for strong electron correlations in the thermoelectric material (Na,Ca)Co_{2}O_{4}

TL;DR

This study measures the specific heat of (Na,Ca)Co_{2}O_{4} to reveal strong electron correlations, explaining its large thermoelectric power through low-dimensionality and frustrated spin structures.

Contribution

It provides direct evidence of strong electron correlations in (Na,Ca)Co_{2}O_{4} via specific heat measurements, linking these correlations to thermoelectric properties.

Findings

b is 48 mJ/molK^2, much larger than simple metals

Indicates strong electron correlations in the material

Correlations likely originate from low-dimensionality and frustrated spins

Abstract

The specific heat of (Na,Ca)Co_{2}O_{4} is measured at low-temperatures to determine the magnitude of the electronic specific-heat coefficient \gamma, in an attempt to gain an insight into the origin of the unusually large thermoelectric power of this compound. It is found that \gamma is as large as 48 mJ/molK^2, which is an order of magnitude larger than \gamma of simple metals. This indicates that (Na,Ca)Co_{2}O_{4} is a strongly-correlated electron system, where the strong correlation probably comes from the low-dimensionality and the frustrated spin structure. We discuss how the large thermopower and its dependence on Ca doping can be understood with the strong electron correlations.