Signatures of Coherent Refraction of Dirac Electrons at Molecular Graphene Interfaces

One of the many interesting features of graphene is the light-like behavior of its electrons near the Dirac points, characterized by a massless dispersion relation. This behavior suggests the possibility of constructing devices, such as Veselago lenses, that can focus electron wavefunctions in a manner analogous to the focusing of light by optical instruments. Molecular graphene, consisting of carbon monoxide molecules arranged on a copper surface so as to confine the electrons to a honeycomb lattice, is an artificial form of graphene that can be controlled on an atomic level, and is thus an ideal candidate for investigating light-like behavior of Dirac fermions. We report experiments that probe the behavior of electrons incident upon a graphene junction through quasiparticle interference measurements of a molecular graphene system in a low-temperature, ultra-high vacuum scanning tunneling microscope. Our results provide evidence of coherent refraction of electrons passing through the junction, akin to light bending at interfaces between mismatched media.