Valley-isospin dependence of the quantum Hall effect in a graphene p-n junction

TL;DR

This paper investigates how valley isospin orientation affects the quantum Hall conductance in graphene p-n junctions, revealing a dependence on edge states, disorder, and strain-induced effects in high magnetic fields.

Contribution

It introduces a model linking valley isospin angles to conductance in graphene p-n junctions, highlighting effects of disorder, edge states, and strain.

Findings

Conductance depends on valley isospin angle as (e^2/h)(1-cos Phi).

Disorder does not affect the conductance plateau, but edge states can destabilize it.

Strain shifts the conductance plateau by rotating valley isospin.

Abstract

We calculate the conductance G of a bipolar junction in a graphene nanoribbon, in the high-magnetic field regime where the Hall conductance in the p-doped and n-doped regions is 2e^2/h. In the absence of intervalley scattering, the result G=(e^2/h)(1-cos Phi) depends only on the angle Phi between the valley isospins (= Bloch vectors representing the spinor of the valley polarization) at the two opposite edges. This plateau in the conductance versus Fermi energy is insensitive to electrostatic disorder, while it is destabilized by the dispersionless edge state which may exist at a zigzag boundary. A strain-induced vector potential shifts the conductance plateau up or down by rotating the valley isospin.