Investigation of Planckian behavior in a high-conductivity oxide : PdCrO2

Abstract

The layered delafossite metal PdCrO2 is a natural heterostructure ofhighly conductive Pd layers Kondo coupled to localized spins in the adjacent Mott insulating CrO2 layers. At high temperatures T it has a T-linearresistivity which is not seen in the isostructural but non-magnetic PdCoO2.The strength of the Kondo coupling is known, as-grown crystals are extremelyhigh purity and the Fermi surface is both very simple and experimentally known. It is therefore an ideal material platform in which to investigate 'Planckianmetal' physics. We do this by means of controlled introduction of point disorder, measurement of the thermal conductivity and Lorenz ratio and studying the sources of its high temperature entropy. The T-linear resistivity is seen to be due mainly to elastic scattering and to arise from a sum of several scattering mechanisms. Remarkably, this sum leads to a scattering rate within 10% of the Planckian value of kBT/ℏ.