Tunneling spectroscopy of bound and resonant states in superconducting proximity structures

Scanning tunneling microscopy and spectroscopy are employed in order to map with nanometer resolution the local quasi-particle density of states in su perconducting proximity structures. Our experimental configuration is uniqu e, in that the tunneling current flows in parallel to the interfaces betwee n different materials. We focus here on the measurement of bound and resona nt states, arising from multiple Andreev reflections of quasi-particles pro pagating in a plane perpendicular to the tunneling current. (C) 1999 Elsevi er Science B.V. All rights reserved.