Undergraduate experiment in superconductor 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 thick superconducting niobium film with a transition temperature T-c approximate to 7 K. By fitting the results to Blonder-Tinkham-Klapwijk theory using a finite lifetime of quasiparticles, we obtain a superconducting gap energy Delta approximate to 1.53 meV, a lower bound to the Fermi velocity nu(F) >= 3.1 x 10(7) cm/s, and a BCS coherence length xi approximate to 43 nm for niobium. These results are in good agreement with previous measurements. (C) 2012 American Association of Physics Teachers.