Universal conductivity and the electrodynamics of graphite at high pressures

TL;DR

This study investigates how high pressure affects the in-plane electrodynamics of graphite, revealing an increase in free charge carriers and a surprising robustness of its universal quantum conductance despite structural changes.

Contribution

It combines infrared spectroscopy and ab initio calculations to show pressure-induced enhancements in charge density and the persistence of universal conductance in graphite.

Findings

Drude term increases with pressure due to higher charge densities.

Mid-infrared optical conductivity remains nearly constant up to 7 GPa.

Universal quantum conductance of graphite is robust under high pressure.

Abstract

We address the in-plane pressure-dependent electrodynamics of graphite through synchrotron based infrared spectroscopy and ab initio Density Functional Theory calculations. The Drude term remarkably increases upon pressure application, as a consequence of an enhancement of both electron and hole charge densities. This is due to the growth of the band dispersion along the k_z direction between the K and H points of the Brillouin zone. On the other hand, the mid-infrared optical conductivity between 800 and 5000 cm-1 is almost flat, and very weakly pressure dependent, at least up to 7 GPa. This demonstrates a surprising robustness of the graphene-like universal quantum conductance of graphite, even when the interlayer distance is significantly reduced.