Professor MICHAEL F. CROMMIE
Department of Physics
U.C. Berkeley

Imaging Dirac Fermions in a Two-dimensional Sheet of Carbon

Abstract:

Graphene, a single atomic layer of carbon, has generated much excitement due to its novel electronic, optical, and mechanical properties. Part of this excitement arises from the fact that electrons in graphene behave like massless relativistic particles (Dirac fermions). Novel phenomena have been predicted to arise from the interplay between these Dirac fermions and various graphene imperfections and excitations. Scanning tunneling microscopy is an ideal tool to study such phenomena at the nanometer scale. We have used this technique to explore the local properties of back-gated graphene flake devices, a configuration that allows us to spatially resolve graphene electronic behavior as a function of device charge carrier density. We find that graphene tunnel spectra exhibit pronounced features arising from different manybody excitations, and our measurements reveal unexpected electronic interference patterns caused by electrons scattering off of electronic density inhomogeneities ("charge puddles"). Our ultra-high spatial resolution has allowed us to determine the origin of these charge puddles.