Probing the electron-electron interaction in a diffusive gold wire using a controllable Josephson junction

We have studied the critical current of a diffusive superconductor - normal metal - superconductor (SNS) Josephson junction as a function of the electron energy distribution in the normal region. This was realized in a 4 terminal device, in which a mesoscopic gold wire between two electron reservoirs is coupled in its center to two superconducting electrodes. By varying the length of the wire and applying a voltage over it we are able to control the electron distribution function in the center of the wire, which forms the normal region of the SNS junction. The observed voltage and temperature dependence are in good agreement with the existing theory on diffusive SNS junctions, except for low energies. However, an electron-electron interaction time $\tau_0$ =10 ps was found, which is three orders of magnitude faster than expected from theory.