Friedel Oscillation-Induced Energy Gap Manifested as Transport Asymmetry   at Monolayer-Bilayer Graphene Boundaries
  We show that Friedel charge oscillation near an interface opens a gap at the Fermi energy for electrons with wave vectors perpendicular to the interface. If the Friedel gaps on two sides of the interface are different, a nonequlibrium effect - shifting of these gaps under bias - leads to asymmetric transport upon reversing the bias polarity. The predicted transport asymmetry is revealed by scanning tunneling potentiometry at monolayer-bilayer interfaces in epitaxial graphene on SiC (0001). This intriguing interfacial transport behavior opens a new avenue towards novel quantum functions such as quantum switching. 
Kendal W. Clark, X.-G. Zhang, Gong Gu, Jewook Park, Guowei He, R. M.   Feenstra, and An-Ping Li
cond-mat.mes-hall