Equilibration of Quantum hall edges in symmetry broken bilayer graphene

TL;DR

This study investigates quantum Hall edge equilibration in bilayer graphene, revealing spin-dependent partial mixing in unipolar regimes and complete mixing in bipolar regimes due to Landau level collapse at sharp pn junctions.

Contribution

It demonstrates how Landau level collapse at sharp pn junctions causes complete edge state mixing in bilayer graphene, advancing understanding of quantum Hall edge behavior.

Findings

Partial equilibration in unipolar regimes based on spin polarization.

Complete edge state mixing in bipolar regimes due to Landau level collapse.

Consistent with existing theory on Landau level behavior at pn junctions.

Abstract

Equilibration of quantum Hall edges is studied in a high quality dual gated bilayer graphene device in both unipolar and bipolar regime when all the degeneracies of the zero energy Landau level are completely lifted. We find that in the unipolar regime when the filling factor under the top gate region is higher than the back gate filling factor, the equilibration is partial based on their spin polarization. However, the complete mixing of the edge states is observed in the bipolar regime irrespective of their spin configurations due to the Landau level collapsing at the sharp pn junction in our thin hBN (~ 15 nm) encapsulated device, in consistent with the existing theory.