Aperiodic conductivity oscillations in quasiballistic graphene heterojunctions.

We observe conductivity oscillations with aperiodic spacing to only one side of the tunneling current in a dual-gated graphene field effect transistor with an n-p-n type potential barrier. The spacing and width of these oscillations were found to be inconsistent with pure Fabry-Perot-type interferences, but are in quantitative agreement with theoretical predictions that attribute them to resonant tunneling through quasibound impurity states. This observation may be understood as another signature of Klein tunneling in graphene heterojunctions and is of importance for future development and modeling of graphene based nanoelectronic devices. [ABSTRACT FROM AUTHOR]