Scanning tunneling potentiometry of magnetotransport in graphene

In this work, I will show scanning tunneling potentiometry (STP) measurements of quasiparticle flow around electrostatically defined, micron-scale quantum wells in ultraclean graphene over a range of carrier densities and applied magnetic fields approaching the quantum Hall regime. These STP measurements reveal complex interference patterns that appear in the ballistic regime and reflect the underlying shape of the graphene Fermi surface. As magnetic fields are applied, we observe changes in the local potential profile that reflect the quasiclassical motion of the carriers around the quantum well. As the field is increased, our measurements reveal signatures of the carriers becoming semi-localized around the potential. We interpret our results in the context of localized states and finite conductance paths that form in the presence of disorder in quantum Hall systems.