The Origin of Anomalous Low-Temperature Downturns in the Thermal Conductivity of Cuprates

TL;DR

This paper explains the low-temperature downturn in cuprates' thermal conductivity as a result of phonon-electron thermal decoupling, which causes a heat transfer bottleneck and affects heat current measurements.

Contribution

It introduces a model for phonon-electron decoupling explaining the thermal conductivity downturn in cuprates at very low temperatures.

Findings

Good agreement with experimental data in normal and superconducting states.

Temperature and magnetic field dependence of thermal conductivity explained.

Decoupling limits electron contribution to heat transport at low T.

Abstract

We show that the anomalous decrease in the thermal conductivity of cuprates below 300 mK, as has been observed recently in several cuprate materials including Pr$_{2-x}$Ce$_x$CuO$_{7-\delta}$ in the field-induced normal state, is due to the thermal decoupling of phonons and electrons in the sample. Upon lowering the temperature, the phonon-electron heat transfer rate decreases and, as a result, a heat current bottleneck develops between the phonons, which can in some cases be primarily responsible for heating the sample, and the electrons. The contribution that the electrons make to the total low-$T$ heat current is thus limited by the phonon-electron heat transfer rate, and falls rapidly with decreasing temperature, resulting in the apparent low-$T$ downturn of the thermal conductivity. We obtain the temperature and magnetic field dependence of the low-$T$ thermal conductivity in the presence of phonon-electron thermal decoupling and find good agreement with the data in both the normal and superconducting states.