Energy gaps and layer polarization of integer and fractional quantum Hall states in bilayer graphene

TL;DR

This study explores how layer polarization influences the energy gaps of integer and fractional quantum Hall states in bilayer graphene, revealing distinct phases and the importance of electric and magnetic fields in stabilizing these states.

Contribution

It provides new insights into the role of layer polarization in quantum Hall states of bilayer graphene, including the discovery of a previously unobserved interlayer coherent phase.

Findings

Layer polarized state at ν=1 has a larger energy gap stabilized by high electric field.

Interlayer coherent state at ν=1 has a smaller gap stabilized by large magnetic field.

Fractional states like ν=2/3 and features at ν=1/2 are observed only at finite electric and magnetic fields.

Abstract

Owing to the spin, valley, and orbital symmetries, the lowest Landau level (LL) in bilayer graphene exhibits multicomponent quantum Hall ferromagnetism. Using transport spectroscopy, we investigate the energy gaps of integer and fractional quantum Hall states in bilayer graphene with controlled layer polarization. The state at filling factor {\nu}=1 has two distinct phases: a layer polarized state that has a larger energy gap and is stabilized by high electric field, and a hitherto unobserved interlayer coherent state with a smaller gap that is stabilized by large magnetic field. In contrast, the {\nu}=2/3 quantum Hall state and a feature at {\nu}=1/2 are only resolved at finite electric field and large magnetic field. These results underscore the importance of controlling layer polarization in understanding the competing symmetries in the unusual QH system of BLG.