Achieving the Theoretical Depairing Current Limit in Superconducting Nanomesh Films

We show the theoretical depairing current limit can be achieved in a robust fashion in highly ordered superconductor nanomesh films having spatial periodicities smaller than both the superconducting coherence length and the magnetic penetration depth. For a niobium nanomesh film with 34 nm spatial periodicity, the experimental critical current density is enhanced by more than 17 times over the continuous film and is in good agreement with the depairing limit over the entire measured temperature range. The nanomesh superconductors are also less susceptible to thermal fluctuations when compared to nanowire superconductors. T_c values similar to the bulk film are achieved, and the nanomeshes are capable of retaining superconductivity to higher fields relative to the bulk. In addition, periodic oscillations in T_c are observed as a function of field, reflecting the highly ordered nanomesh structure

Scanning Tunneling Microscopy Characterization of the Electrical Properties of Wrinkles in Exfoliated Graphene Monolayers

We report on the scanning tunneling microscopy study of a new class of corrugations in exfoliated monolayer graphene sheets, that is, wrinkles ~10 nm in width and ~3 nm in height. We found such corrugations to be ubiquitous in graphene and have distinctly different properties when compared to other regions of graphene. In particular, a “three-for-six” triangular pattern of atoms is exclusively and consistently observed on wrinkles, suggesting the local curvature of the wrinkle provides a sufficient perturbation to break the 6-fold symmetry of the graphene lattice. Through scanning tunneling spectroscopy, we further demonstrate that the wrinkles have lower electrical conductance and are characterized by the presence of midgap states, which is in agreement with recent theoretical predictions. The observed wrinkles are likely important for understanding the electrical properties of graphene