Competing Fractional Quantum Hall and Electron Solid Phases in Graphene

TL;DR

This paper reports the experimental observation of reentrant integer quantum Hall effect in graphene, revealing a competition between fractional quantum Hall states and electron solid phases, with a tunable phase diagram influenced by spin and valley degrees of freedom.

Contribution

It provides the first detailed phase diagram of electron liquid-solid transition in graphene, highlighting the role of spin and valley degrees of freedom in these competing phases.

Findings

Reentrant integer quantum Hall effect observed in graphene's N=2 Landau level.

Melting temperature of electron solid scales with magnetic field.

Phase diagram constructed showing competition between quantum Hall states and electron solids.

Abstract

We report experimental observation of the reentrant integer quantum Hall effect in graphene, appearing in the N$=$2 Landau level. Similar to high-mobility GaAs/AlGaAs heterostructures, the effect is due to a competition between incompressible fractional quantum Hall states, and electron solid phases. The tunability of graphene allows us to measure the $B$-$T$ phase diagram of the electron-solid phase. The hierarchy of reentrant states suggest spin and valley degrees of freedom play a role in determining the ground state energy. We find that the melting temperature scales with magnetic field, and construct a phase diagram of the electron liquid-solid transition.