Magnetothermal Transport of Oriented Graphite at Low Temperatures

We have studied the magnetic field dependence of the thermal conductivity $κ(T,B)$ 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.

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