Undergraduate experiment in point-contact spectroscopy with a Nb/Au junction

TL;DR

This paper details an undergraduate experiment using point-contact spectroscopy on a Nb/Au junction to measure superconducting properties, demonstrating practical application of theoretical models and obtaining key superconducting parameters.

Contribution

It presents a practical undergraduate laboratory experiment performing point-contact spectroscopy on niobium, including data analysis with Blonder-Tinkham-Klapwijk theory to extract superconducting parameters.

Findings

Superconducting gap energy .53 meV

Fermi velocity lower bound .31 ^{-7} cm/s

BCS coherence length  43 nm

Abstract

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.