Slow non-exponential phase relaxation and enhanced mesoscopic kinetic inductance noise in disordered superconductors

TL;DR

This paper develops a theory explaining slow, non-exponential phase relaxation in disordered superconductors, leading to enhanced mesoscopic noise and implications for kinetic inductance devices.

Contribution

It introduces a quantitative model showing how superconducting coherence length causes slow, non-exponential phase relaxation, increasing mesoscopic noise in disordered superconductors.

Findings

Superconducting coherence length limits quantum interference effects.

Phase relaxation decay is non-exponential in superconductors.

Mesoscopic noise amplitude scales non-linearly with defect strength and number.

Abstract

Mesoscopic low frequency noise in electrical characteristics of disordered conductors is a result of dynamic quantum interference pattern due to motion of defects. This has been firmly established by demonstrating the characteristic partial suppression of the noise amplitude by the dephasing effect of a weak external magnetic field. The spatial correlation of the quantum interference pattern in disordered normal state conductors is invariably limited by the exponential phase relaxation due to inelastic processes. In this paper we develop a quantitative theory of the mesoscopic noise in the s-wave superconducting phase of a strongly disordered superconductor (such that the superconducting coherence length is much longer than the mean free path). We find that the superconducting coherence length limits the quantum interference effects in superconductors. However, in contrast to the normal phase, the decay of the phase relaxation on the scale of the superconducting coherence length is non-exponential. This unusual slow relaxation manifests in the enhanced amplitude of the mesoscopic noise in superconductors and a peculiar non-linear scaling of the amplitude with the strength/number of mobile defects in very thin superconducting films and wires (effectively 2D and 1D with respect to the superconducting coherence length). Mesoscopic noise sets a natural limit on the quality of kinetic inductance elements.