Nonequilibrium noise and current fluctuations at the superconducting phase transition

TL;DR

This paper investigates non-Gaussian current fluctuations near the superconducting phase transition in a mesoscopic NSN circuit, revealing enhanced higher cumulants and potential excess noise surpassing thermal levels.

Contribution

It introduces a detailed analysis of out-of-equilibrium current fluctuations at the superconducting transition, highlighting the role of order parameter fluctuations in mesoscopic circuits.

Findings

Higher cumulants of current fluctuations are parametrically enhanced.

Excess current noise can reach or exceed thermal noise levels.

Fluctuations are mediated by preformed Cooper pairs near the transition.

Abstract

We study non-Gaussian out-of-equilibrium current fluctuations in a mesoscopic NSN circuit at the point of a superconducting phase transition. The setup consists of a voltage-biased thin film nanobridge superconductor (S) connected to two normal-metal (N) leads by tunnel junctions. We find that above a critical temperature fluctuations of the superconducting order parameter associated with the preformed Cooper pairs mediate inelastic electron scattering that promotes strong current fluctuations. Though the conductance is suppressed due to the depletion of the quasiparticle density of states, higher cumulants of current fluctuations are parametrically enhanced. We identify experimentally relevant transport regime where excess current noise may reach or even exceed the level of the thermal noise.