Roles of high-frequency optical phonons in the physical properties of the conductive delafossite PdCoO2

We report physical properties of the conductive oxide PdCoO2 in the layered delafossite structure through measurements of the electrical resistivity, specific heat, magnetic susceptibility, polarized Raman spectra and infrared absorption. We observed two prominent Raman peaks at 520 and 712 cm(-1). The presence of these high frequency optical phonons is essential to explain the temperature dependence of the specific heat and the resistivity. No sign of superconductivity was detected in electrical resistivity and AC susceptibility down to 15 mK.