Strongly disordered TiN and NbTiN s-wave superconductors probed by microwave electrodynamics

TL;DR

This study investigates how strong disorder affects superconductivity in TiN and NbTiN thin films by measuring microwave electrodynamics, revealing deviations from conventional theory linked to changes in quasiparticle states.

Contribution

It provides experimental evidence of disorder-induced modifications in superconducting properties and introduces an effective pair breaker model to explain these effects.

Findings

Electromagnetic response evolves with disorder

Deviations from Mattis-Bardeen theory observed

Changes linked to quasiparticle density of states

Abstract

We probe the effects of strong disorder (2.4 < kFl < 8.6) on superconductivity in thin films of niobium titanium nitride and titanium nitride by measuring the microwave electrodynamics in coplanar waveguide resonators. We find a gradual evolution of the electromagnetic response with disorder, deviating from Mattis-Bardeen theory, for both materials. This result can be understood as due to changes in the quasiparticle density of states, induced by the short elastic scattering length. The observations are consistent with a model using an effective pair breaker, dependent on the level of disorder.