Finite quasiparticle lifetime in disordered superconductors

Abstract

We investigate the complex conductivity of a highly disordered MoC superconducting film with $k_{F}l\approx 1$, where $k_F$ is the Fermi wavenumber and $l$ is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature $T_c$. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, $\ddot{I}„$, offers a perfect description of the experimentally observed complex conductivity. We show that $\ddot{I}„$ is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by the scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

8 pages, 10 figures