Even denominator fractional quantum Hall states at an isospin transition in monolayer graphene

TL;DR

This paper demonstrates the realization of a quantum Hall transition in monolayer graphene, revealing novel even denominator fractional quantum Hall states linked to isospin pairing and symmetry breaking.

Contribution

It introduces an experimental control of sublattice symmetry breaking to observe a transition analogous to Neél-to-valence bond solid in graphene's Landau levels, uncovering new fractional quantum Hall states.

Findings

Observation of isospin transitions in fractional quantum Hall states near charge neutrality.

Emergence of incompressible even denominator fractional quantum Hall states at specific filling factors.

Evidence of pairing between composite fermions on different sublattices.

Abstract

Magnetic fields quench the kinetic energy of two dimensional electrons, confining them to highly degenerate Landau levels. In the absence of disorder, the ground state at partial Landau level filling is determined only by Coulomb interactions, leading to a variety of correlation-driven phenomena. Here, we realize a quantum Hall analog of the Ne\'el-to-valence bond solid transition within the spin- and sublattice- degenerate monolayer graphene zero energy Landau level by experimentally controlling substrate-induced sublattice symmetry breaking. The transition is marked by unusual isospin transitions in odd denominator fractional quantum Hall states for filling factors $\nu$ near charge neutrality, and the unexpected appearance of incompressible even denominator fractional quantum Hall states at $\nu=\pm1/2$ and $\pm1/4$ associated with pairing between composite fermions on different carbon sublattices.