Magnetothermal Transport of Oriented Graphite at Low Temperatures

TL;DR

This study investigates how magnetic fields affect the thermal conductivity of highly oriented graphite at very low temperatures, revealing deviations from classical laws and oscillations linked to quantum effects and phonon interactions.

Contribution

It provides new insights into the magnetothermal transport properties of graphite, especially the phonon-mediated oscillations and deviations from Wiedemann-Franz law at low temperatures.

Findings

Deviations from Wiedemann-Franz law near metal-insulator transition

Oscillations in thermal conductivity correlated with Landau quantization

Thermal oscillation amplitude increases with temperature following a T^3 law

Abstract

We have studied the magnetic field dependence of the thermal conductivity $\kappa(T,B)$ of highly oriented pyrolytic graphite samples at temperatures 0.2K$ \le T < 10$K and fields 0T$ \le B \le 9$T. The samples show clear deviations from the Wiedemann-Franz law with a kink behavior at fields $B \sim 0.1 $T near the metal-insulator transition observed in electrical resistivity measurements. We further show that the oscillations in the thermal conductivity at the quantum limit $B > 1 $T, which are correlated with the Landau quantization observed in Hall measurements, increase in amplitude with temperature following a $\sim T^3$ law at $T > 0.2 $K and show a maximum at $T \sim 6 $K, suggesting that they are phonons mediated.