Two phase transitions induced by a magnetic field in graphite

TL;DR

This study reveals that a strong magnetic field induces two successive phase transitions in graphite, each creating a bulk energy gap and coexisting with in-plane metallicity, suggesting edge-state transport phenomena.

Contribution

First experimental observation of two distinct magnetic-field-induced phase transitions in graphite with unique electronic properties.

Findings

Two successive phase transitions with finite field windows

Energy gap opens in out-of-plane conductivity in both states

Coexistence of bulk energy gap with in-plane metallicity

Abstract

Different instabilities have been speculated for a three-dimensional electron gas confined to its lowest Landau level. The phase transition induced in graphite by a strong magnetic field, and believed to be a Charge Density Wave (CDW), is the only experimentally established case of such instabilities. Studying the magnetoresistance in graphite for the first time up to 80 T, we find that the magnetic field induces two successive phase transitions, consisting of two distinct ordered states each restricted to a finite field window. In both states, an energy gap opens up in the out-of-plane conductivity and coexists with an unexpected in-plane metallicity for a fully gap bulk system. Such peculiar metallicity may arise as a consequence of edge-state transport expected to develop in presence of a bulk gap.