Investigation of Planckian behavior in a high-conductivity oxide: PdCrO$_2$

TL;DR

This study investigates the Planckian behavior in the high-conductivity oxide PdCrO$_2$, revealing that its high-temperature resistivity is mainly due to elastic scattering with a rate close to the fundamental Planckian limit.

Contribution

The paper demonstrates that the high-temperature resistivity in PdCrO$_2$ arises from multiple elastic scattering mechanisms with a rate near the Planckian limit, providing insights into 'Planckian metal' physics.

Findings

Resistivity is dominated by elastic scattering mechanisms.

Scattering rate is within 10% of the Planckian limit.

High purity crystals enable precise investigation of scattering processes.

Abstract

The layered delafossite metal PdCrO$_2$ is a natural heterostructure of highly conductive Pd layers Kondo coupled to localized spins in the adjacent Mott insulating CrO$_2$ layers. At high temperatures $T$ it has a $T$-linear resistivity which is not seen in the isostructural but non-magnetic PdCoO$_2$. The strength of the Kondo coupling is known, as-grown crystals are extremely high purity and the Fermi surface is both very simple and experimentally known. It is therefore an ideal material platform in which to investigate 'Planckian metal' 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 $k_BT/$$\hbar$.