Observation of bound quasiparticle states in thin Au islands by scanning tunneling microscopy

Abstract

Cryogenic scanning tunneling microscopy has been used to measure the structure and the local electronic density of states of thin gold islands in metallic contact with a bulk superconducting ${\mathrm{NbSe}}_2$ crystal. Peaks are observed in the tunneling conductance below the energy gap corresponding to discrete bound quasiparticle states in the gold. The energies and spatial dependence of the bound states imply that the superconducting pair potential falls off abruptly at the Au-${\mathrm{NgSe}}_2$ interface.