High-field Righi-Leduc effect and lattice thermal conductivity of potassium

Abstract

We report measurements of the high-field Righi-Leduc coefficient of polycrystalline specimens of potassium. The measurements were made between 2 and 9 K for magnetic fields up to 9 T on specimens having residual-resistance ratios ranging from 2100 to 7300. We find that the lattice thermal conductivity causes the low-temperature Righi-Leduc coefficient to be field dependent. Using simple theoretical ideas, we are able to determine the magnitude and temperature dependence of the lattice conductivity and demonstrate that it is not large enough to be responsible for the previously observed field dependence in the transverse thermal magnetoconductivity of potassium. After correcting the measured Righi-Leduc coefficient for the lattice contribution, we find it close to the theoretical predictions. When compared to the Hall coefficient, we find a substantial deviation from the Wiedemann-Franz law, in direct contrast to the theoretical predictions. By combining measurements of the thermal gradients in both directions perpendicular to the magnetic field we are able to operationally define an average thermal scattering time ${\tau }_{\mathrm{th}}$. We find our values of ${\tau }_{\mathrm{th}}$ are consistent with theoretical predictions.