Atomic layer superconductivity

Abstract

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 4 K in fields of up to 6 T to extract the critical temperature TC for the onset of superconductivity. We find TC = 1.5 K for a single layer Pb on Si(111), and a critical out‐of‐plane field of 150 mT. This deviates from bulk Pb, where TC = 7.2 K and HC = 80 mT are reported. Our results provide the temperature dependence of the superconducting gap 2 Δ. A description of this dependence in the framework of the Bardeen–Cooper–Schrieffer theory indicates an energy gap of 2 Δ0 = 0.7 meV, considerably less than the 2.7 meV 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 0.38 K. 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 20 nm away from the Pb island edge at 0.38 K. © 2014 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.