Large Thermopower Anisotropy In Pdcoo2 Thin Films

Motivated by recent theoretical studies predicting a large thermopower anisotropy in the layered delafossite PdCoO2, we have used pulsed laser deposition to synthesize thin films on (0001)-oriented and offcut Al2O3 substrates. By combining transport measurements on films with different offcut angles, tensor rotation relations, and an iterative fit procedure for the transport parameters, we have determined the resistivity and the thermopower along the main crystallographic axes in the temperature range 300-815 K. The data reveal a small positive Seebeck coefficient along the delafossite planes and a large negative Seebeck coefficient perpendicular to the planes, in excellent agreement with density functional calculations in the presence of moderate Coulomb correlations. The methodology introduced here is generally applicable for measurements of the thermoelectric properties of materials with highly anisotropic electronic structures.