Ballistic-Ohmic quantum Hall plateau transition in a graphene p-n junction

Recent quantum Hall experiments conducted on disordered graphene p-n junction provide evidence that the junction resistance could be described by a simple Ohmic sum of the n and p mediums' resistances. However in the ballistic limit, theory predicts the existence of chirality-dependent quantum Hall plateaus in a p-n junction. We show that two distinctively separate processes are required for this ballistic-Ohmic plateau transition, namely, (i) hole/electron Landau states mixing and (ii) valley isospin dilution of the incident Landau edge state. These conclusions are obtained by a simple scattering theory argument, and confirmed numerically by performing ensembles of quantum magnetotransport calculations on a 0.1 mu m wide disordered graphene p-n junction within the tight-binding model. The former process is achieved by p-n interface roughness, where a p-n interface disorder with a root-mean-square roughness of 10 nm was found to suffice under typical experimental conditions. The latter process is mediated by extrinsic edge roughness for an armchair edge ribbon and by intrinsic localized intervalley scattering centers at the edge of the p-n interface for a zigzag ribbon. In light of these results, we also examine why higher Ohmic-type plateaus are less likely to be observable in experiments.