Condensed Matter Seminars

It has been four years since the first successful isolation of graphene, a single atomic sheet of carbon, and enthusiasm for this material is still growing. Part of this excitement arises from the fact that electrons in graphene behave as massless "relativistic" particles (Dirac fermions) with an effective speed of light equal to c/300. Microscopic disorders in graphene, such as ripples in the carbon sheet or static "puddles" of charge, profoundly alter the behavior of these electrons. I will describe our recent experiments aimed at directly probing these perturbations and imaging their influence on Dirac fermions down to the atomic scale. Our measurements, performed using the techniques of scanning tunneling microscopy and spectroscopy, reveal unexpected electronic interference patterns that vary as a function of both electron energy and applied electric field (via a gate electrode). I will show that electron interference in graphene nanodevices arises from scattering off of static puddles of electrons, and that these puddles are caused by charged impurities underneath the graphene sheet.