Magnetoconductance fluctuations and re-entrance effect in normal-metal/superconductor nanostructures

The proximity of a superconductor strongly influences the electronic proper ties of a normal metal. We report on measurements of the re-entrant behavio r of the conductance of mesoscopic gold/niobium heterostructures. At very l ow temperature a novel peak shows up in the conductance vs, voltage charact eristics which can be suppressed by small magnetic fields of several mT. Fu rthermore, the proximity effect gives rise to unique electronic interferenc e contributions resulting in an increase of the rms of the conductance fluc tuations by a factor of 2 root 2 in our heterostructures.