Conductance regimes in superconducting junctions of atomic size

Abstract

A scanning tunneling microscope has been used to study the different conductance regimes of superconducting Pb junctions of atomic size. Measurement of the apparent tunneling barrier and imaging of probed areas before and after the spectroscopic measurement give information on the surface condition and the geometry of the junction. The evolution of the differential conductance curves is followed from the tunneling regime to contact as the junction is varied in a continuous and controlled manner. The oberved evolution of the conductance follows quantitatively Octavio-Tinkham-Blander-Klapwijk theory with the addition of a lifetime broadening parameter, which accounts for the observed smearing of the superconducting gap features.