The effect of phonon-electron thermal decoupling on the low-T thermal conductivity data of cuprates

摘要

We describe how the anomalous decrease in the thermal conductivity, which has been observed in several cuprates at sub-Kelvin temperatures, occurs because of the thermal decoupling of phonons and electrons. In typical experimental conditions for these ultra-low-T thermal conductivity measurements, the initial heat current is provided to the electrons in the sample mainly by phonons. The phonon-electron heat transfer rate falls rapidly with decreasing temperature and, below a characteristic temperature scale that we identify to be roughly 200 Mk in typical cuprates, a heat-current bottleneck develops. The electronic heat current thus becomes limited by electron-phonon heat transfer and acquires an anomalous temperature dependence. This results in the apparent low-T downturn of the thermal conductivity. We account for the temperature and magnetic field dependence of the low-T thermal conductivity in both the normal and superconducting states, obtaining quantitative agreement with the data.