Impact of Surface Conditions on the Superconductivity of Si(111)-(√7 × √3)-In

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We performed low-temperature scanning tunneling microscopy and spectroscopy on Si(111)-(√7 × √3)-In in magnetic fields. Superconducting vortices were observed by mapping zero-bias conductance in an area consisting of flat terraces separated by atomic steps. While vortices in the terrace regions have an isotropic shape with a normal-state core, those at the atomic steps have anisotropic shapes and the superconductivity is only weakly suppressed in the cores. These properties are understood as a crossover from a normal vortex to a Josephson vortex. We conclude that the atomic steps work as Josephson junctions limiting the density of supercurrents. [DOI: 10.1380/ejssnt.2015.151]