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 superconducting proximity structures. Our experimental configuration is unique, in that the tunneling current flows in parallel to the interfaces between different materials. We focus here on the measurement of bound and resonant states, arising from multiple Andreev reflections of quasi-particles propagating in a plane perpendicular to the tunneling current.