Orateur
Description
Kinetic inductance $L_\mathrm{kin}$ quantifies the inertia of the superconducting condensate and hence the low-temperature electrodynamics of superconducting microwave circuitry. We directly probe the inductive response in the broadband reactance of superconducting granular aluminum and titanium nitride from MHz to GHz frequencies, $\mathrm{Im}(𝑍) = \omega \cdot L_\mathrm{kin}$, by Corbino reflectometry. Furthermore, we observe up to ten harmonics of an unconventional mode in the same experiment. The dynamics of this mode is governed by the collective response of the superconducting condensate, enabling a second independent determination of the kinetic inductance. We report low-temperature kinetic inductances up to 29 nH/sq for a titanium nitride thin film in the vicinity of the superconductor-insulator transition. The corresponding low-temperature superfluid stiffness is on the order of $T_\mathrm{c}$, consistent with a phase-driven superconducting transition.
At elevated temperatures we observe that the superfluid stiffness deviates from the two-fluid expectation of continuous suppression. This happens in the vicinity of the crossing with the Kosterlitz-Thouless universal line. The superfluid stiffness acquires a strong frequency dependence, which we interpret as a signature of finite frequency effects on thermal phase fluctuations of the superconducting condensate.