Size-Dependent Superconductivity of Pb Islands under Magnetic Fields Studied by Low-Temperature Scanning Tunneling Microscopy/Spectroscopy

摘要

Using a low-temperature scanning tunneling microscope, we investigated the superconducting gap of single-crystalline Pb islands, approximately 100 nm in diameter with 11-13 monolayers (3-4 nm) in thickness, under magnetic fields. The superconducting gap was observed under magnetic fields up to 2.2 T, higher than the critical field of bulk Pb. The critical fields of the Pb islands were evaluated from the magnetic field dependence of the zero-bias conductances. We found that the critical field depends on the volume V of the Pb islands as V~(-1/2).