Graphite in the bi-layer regime: in-plane transport

The dependence of in-plane resistivity of HOPG graphite on temperature is studied both experimentally and theoretically over a wide range of temperatures(up to $\sim$900 K). For temperatures larger than the next-to-nearest-plane coupling which gives rise to an overlap of the valence and conduction bands, but still below the nearest-plane coupling, graphite can be viewed as a stack of bilayers. In this regime, the in-plane conductivity $\sigma$ is supposed to scale as $T\tau$, where $\tau$ is the scattering time. For conventional electron-phonon scattering, $\tau\propto 1/T$ and $\sigma$ is supposed to saturate at higher $T$. However, we observe experimentally that $\sigma$ decreases monotonically without any sign of saturation up to the highest temperature measured. We propose two additional scattering mechanisms which lead to a decrease of $\sigma$: intervalley scattering by phonons and multiple intravalley scattering by phonons due to anharmonicity of a layered lattice at high temperatures. A reasonable agreement between theory and experiment is obtained by using this model.