Coherent Refraction Across Atomically-Precise Molecular Graphene Junctions

The construction of functional nanoscopic devices requires an in-depth understanding of electronic transport across interfaces. Electrons in graphene exhibit lightlike behavior due to their massless dispersion relation near the Dirac points; this suggests the ability to construct nanostructures that control electrons analogously to how optical devices such as lenses control light, provided that transport at the interface is understood. Molecular graphene, assembled with atomic manipulation of individual molecules in a low-temperature, ultra-high-vacuum scanning tunneling microscope so as to confine itinerant two-dimensional electrons to a honeycomb lattice, serves as a new tunable form of graphene that features atomically-precise edges and is thus ideal for probing interface transport. We report experiments that use quasiparticle interference measurements to probe the behavior of Dirac electrons incident upon junctions between molecular graphene and a nearly-free two-dimensional electron gas, and between differently-doped regions of molecular graphene. Our results indicate that Dirac electrons are refracted coherently across the junction, analogous to light bending across an interface between two media with mismatched indices of refraction.