Low-voltage current noise in long quantum SINIS junctions

TL;DR

This paper investigates how low-voltage current noise in long SINIS junctions is affected by non-equilibrium populations of sub-gap states, revealing a significant enhancement of the Fano factor due to Landau-Zener transitions and inelastic relaxation.

Contribution

It introduces a detailed analysis of non-equilibrium noise in SINIS junctions, linking Landau-Zener transitions to noise enhancement and providing a method to characterize non-equilibrium kinetics.

Findings

Fano factor is drastically enhanced in long SINIS junctions.

Non-equilibrium distribution is driven by Landau-Zener transitions and inelastic relaxation.

Combining dc current and noise measurements allows full characterization of non-equilibrium kinetics.

Abstract

The current noise in long SINIS junctions at low temperatures is sensitive to the population of the sub-gap states which is far from equilibrium even at low bias voltages. Nonequilibrium distribution establishes due to an interplay between voltage-driven inter-level Landau-Zener transitions and intra-level inelastic relaxation. We show that the Fano factor is enhanced drastically, being proportional to the number of times which particle can fly along the Andreev trajectory before it escapes from the level due to inelastic scattering. Combining the dc current and noise measurements one can fully characterize the non-equilibrium kinetics in SINIS junctions.