OBSERVATION OF BOUND QUASI-PARTICLE STATES IN THIN AU ISLANDS BY SCANNING-TUNNELING-MICROSCOPY

Cryogenic scanning tunneling microscopy has been used to measure the s tructure and the local electronic density of states of thin gold islan ds in metallic contact with a bulk superconducting NbSe2 crystal. Peak s are observed in the tunneling conductance below the energy gap corre sponding to discrete bound quasiparticle states in the gold. The energ ies and spatial dependence of the bound states imply that the supercon ducting pair potential falls off abruptly at the Au-NbSe2 interface.