Observation of surface superconductivity and direct vortex imaging of a Pb thin island with a scanning tunneling microscope

Abstract

We report on a scanning tunneling spectroscopy study on vortex imaging and surface superconductivity of a thin type-II superconducting Pb island, which is epitaxially grown on Si substrate and 12 atomic monolayers in thickness. The field dependence of vortex lattice evolution reveals the existence of the surface superconducting layer, which is parallel to the magnetic field in the periphery of the island and disappears above a critical field Hc3 of 3077 G. The Hc3/Hc2 ratio of 1.57 gives a further support for the surface superconductivity.