Charge density waves in graphite; towards the magnetic ultra-quantum limit

TL;DR

This study investigates charge density wave states in graphite under high magnetic fields, revealing their collapse and emergence of an insulating phase with unique surface states near the ultra-quantum limit.

Contribution

It provides experimental evidence of density wave collapse and predicts a new insulating phase with surface states in graphite at ultra-high magnetic fields.

Findings

Collapse of electron and hole density wave states at 52.3 T and 54.2 T

Evidence for a commensurate density wave at 47.1 T

Prediction of an insulating phase above 73.5 T with surface states

Abstract

Graphite is a model system for the study of three-dimensional electrons and holes in the magnetic quantum limit, in which the charges are confined to the lowest Landau levels. We report magneto-transport measurements in pulsed magnetic fields up to 60 T, which resolve the collapse of two density wave states in two, electron and hole, Landau levels at 52.3 and 54.2 T respectively. We report evidence for a commensurate density wave at 47.1 T in the electron Landau level. The theoretical modelling of these results predicts that the ultra-quantum limit is entered above 73.5 T. This state is an insulator, and we discuss its correspondence to the "metallic" state reported earlier. We propose that this (interaction-induced) insulating phase supports surface states that carry no charge or spin within the planes, but does however support charge transport out of plane.