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 (h ω_c ∼ 50 meV), the thermal destruction of Fermi-liquid occurs at the moderate crossover temperature T_M (∼ 200 K), and suggests a new scaling for thermoelectric power S of cobaltates (S ∼ kT/hω_c ∼ T/T_M) at low temperatures. At high temperatures, the dominating incoherent excitation leads to a weak temperature dependent S, and electric resistivity ρ approaches the Mott-limit hale ² ∼ a few mΩ·cm for cobaltates, where a is a lattice constant.