Giant valley-isospin conductance oscillations in ballistic graphene

TL;DR

This paper reports the observation of giant valley-isospin conductance oscillations in ballistic graphene p-n junctions at high magnetic fields, revealing edge-configuration effects through conductance variations dependent on junction position.

Contribution

It demonstrates the first experimental signature of isospin-defined conductance oscillations in graphene p-n junctions, supported by quantum transport calculations.

Findings

Large conductance oscillations of about e^2/h observed

Oscillations depend on p-n junction position

Experimental results align with quantum transport models

Abstract

At high magnetic fields the conductance of graphene is governed by the half-integer quantum Hall effect. By local electrostatic gating a \textit{p-n} junction perpendicular to the graphene edges can be formed, along which quantum Hall channels co-propagate. It has been predicted by Tworzid\l{}o and co-workers that if only the lowest Landau level is filled on both sides of the junction, the conductance is determined by the valley (isospin) polarization at the edges and by the width of the flake. This effect remained hidden so far due to scattering between the channels co-propagating along the \textit{p-n} interface (equilibration). Here we investigate \textit{p-n} junctions in encapsulated graphene with a movable \textit{p-n} interface with which we are able to probe the edge-configuration of graphene flakes. We observe large quantum conductance oscillations on the order of \si{e^2/h} which solely depend on the \textit{p-n} junction position providing the first signature of isospin-defined conductance. Our experiments are underlined by quantum transport calculations.