Quasiparticle recombination time in superconducting tin and normal electronic density of states at the Fermi surface from tunnel junction experiments

Abstract

We have measured the temperature dependence of the effective quasiparticle recombination time in superconducting tin tunnel junctions by current and laser pulse excitation. The experimental times show satisfactory agreement with calculations based on the ray acoustic lifetime model of Eisenmenger et al. taking into account the film thickness dependence of the phonon reabsorption, 2Delta-phonon volume loss processes and phonon transmission from the junction into the substrate and liquid helium. On the basis of the BCS density of thermally excited quasiparticles and simplified rate equations for quasiparticle recombination, and from the analysis of measurements of decaying excess quasiparticle concentrations we obtain a mean valueN 0=(2.73±0.03) 1022 eV-1 cm-3 for the electronic density of states at the Fermi Surface in thin, evaporated tin films. This value differs less than 5% from that obtained from the experimental electronic heat-capacity coefficient of the bulk material.