On the Thermoelectric Properties of Layered Cobaltates

A study on the thermoelectric properties of layered cobaltates is presented, based on the dynamic mean field theory for strongly correlated electron systems. Electron correlation results in a crossover from coherent quasi-particle excitation at low temperature to incoherent excitation at high temperatures in cobaltates. With an extremely narrow quasi-particle bandwidth (\textit{h$\omega $}$_{c} \quad \sim $ 50 meV), the thermal destruction of Fermi-liquid occurs at the moderate crossover temperature $T_{M}$ ($\sim $ 200 K), and suggests a new scaling for thermoelectric power $S$ of cobaltates ($S \quad \sim $ \textit{kT}/\textit{h$\omega $}$_{c} \quad \sim \quad T$/$T_{M}$ ) at low temperatures. At high temperatures, the dominating incoherent excitation leads to a weak temperature dependent $S$, and electric resistivity \textit{$\rho $ }approaches the Mott-limit \textit{ha}/$e^{2} \quad \sim $ a few m$\Omega \cdot $cm for cobaltates, where $a$ is a lattice constant.