Cryogenic scanning tunneling microscopy has been used as a local probe of the superconducting proximity effect across a normal metal–superconductor interface of a short coherence length superconductor. Both the topography and the local electronic density of states were measured on a superconducting NbS${\mathrm{e}}_2$ crystal decorated with nanometer-size Au islands. The presence of a quasiparticle bound state could be inferred even when the probe was located directly on the bare NbS${\mathrm{e}}_2$ surface near an Au island, indicating a severe depression of the pair potential inside the superconductor due to the proximity effect.

• Received 5 June 1995

DOI:https://doi.org/10.1103/PhysRevLett.77.924