Spatially resolved spectroscopy on superconducting proximity nanostructures - art. no. 165420

We investigated the local density of states (LDOS) of a normal metal (N) in good electrical contact with a superconductor (S) as a function of the dis tance x to the NS interface. The sample consists of a pattern of alternate strips of Au and Nb. We used a low-temperature scanning tunneling microscop e to record simultaneously dI/dV(V,x) curves and the topographic profile z( x). Nearby the NS interface, all the spectra show a dip at the Fermi energy but, depending on the geometry, different behaviors can be distinguished. First, when the characteristic size of the normal metal L is much larger th an the coherence length xi (N) = root(h) over barD(N)/2 Delta, the spectral extension of the dip decreases from Delta at the NS interface to zero at d istances x>>xi (N). Second, when L is comparable to xi (N), the apparent ga p in the LDOS is space independent.