MEASUREMENT OF THE EVEN-ODD FREE-ENERGY DIFFERENCE OF AN ISOLATED SUPERCONDUCTOR

We have measured the difference between the free energies of an isolated superconducting electrode with odd and even number of electrons using a Coulomb blockade electrometer. The decrease of this energy difference with increasing temperature is in good agreement with theoretical predictions assuming a BCS density of quasiparticle states, except at the lowest temperatures where the results indicate the presence of an extra energy level inside the gap.