Atomic layer superconductivity

摘要

We present scanning tunneling microscopy (STM) studies of superconductivity of single layer Pb and Pb islands on Si(111). We perform temperature-dependent measurements of the differential conductance from 0.38 to 4K in fields of up to 6T to extract the critical temperature T-C for the onset of superconductivity. We find T-C=1.5K for a single layer Pb on Si(111), and a critical out-of-plane field of 150mT. This deviates from bulk Pb, where T-C=7.2K and H-C=80mT are reported. Our results provide the temperature dependence of the superconducting gap 2 . A description of this dependence in the framework of the Bardeen-Cooper-Schrieffer theory indicates an energy gap of 2 (0)=0.7meV, considerably less than the 2.7meV found for bulk Pb. We observe that the insertion of a single layer Ag between Pb and Si suppresses superconductivity in the Pb film even at the lowest temperature of 0.38K. Pb islands on Ag/Si(111) exhibit superconductivity. Our position-dependent STM studies from a nine-layer tall Pb island into the surrounding non-superconducting Pb wetting layer on Ag/Si(111) reveal an extension of a superconducting gap in spectroscopy up to 20nm away from the Pb island edge at 0.38K. (c) 2014 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.