Microwave response and electrical transport studies of disordered s wave superconductor: NbN thin films

Understand

It is now well known that the properties of the disordered s wave superconductors can deviate significantly from the prediction of standard Bardeen-Cooper-Schrieffer (BCS) theory.

• By measuring the temperature dependence of the resonance frequency, $f_0$, of microwave resonators made from disordered NbTiN and TiN thin films, at low temperatures, below half of the superconducting critical temperature, $T_c$, Driessen et al.
• \cite{driessen2012PRL} demonstrated that $f_0$ vanishes faster than predicted from the BCS theory.
• Here, we report on the temperature dependence of $f_0$ of microwave resonators made from disordered NbN thin films at higher temperatures--- typically from 0.4 to 0.8$T_c$.