Undergraduate experiment in point-contact spectroscopy with a Nb/Au   junction
  We describe an experiment in superconductivity suitable for an advanced undergraduate laboratory. Point-contact spectroscopy is performed by measuring the differential conductance between an electrochemically etched gold tip and a 100-nm superconducting niobium film with a transition temperature Tc ~= 7 K. By fitting the results to Blonder-Tinkham-Klapwijk theory using a finite lifetime of quasiparticles, we obtain a superconducting gap energy \delta ~= 1.53 meV, a lower bound to the Fermi velocity vF >= 3.1 x 10^-7 cm/s, and a BCS coherence length \zeta ~= 43 nm for niobium. These results are in good agreement with previous measurements. 
L. Janson, M. Klein, H. Lewis, A. Lucas, A. Marantan, K. Luna
physics.ed-ph cond-mat.supr-con