Energy dependence of current noise in double-barrier normal-superconducting structures

TL;DR

This paper provides a theoretical analysis of how current noise energy dependence in a normal-normal-superconductor structure reveals information about interface channel distributions, with explicit formulas for noise based on junction properties.

Contribution

It introduces explicit expressions for current noise in N-N'-S structures considering arbitrary channel transparency distributions, linking noise behavior to interface properties.

Findings

Differential Fano factor depends on junction transparencies and conductance ratio.

Measurement of conductance and noise can probe interface channel distributions.

Explicit formulas valid for arbitrary transparency distributions.

Abstract

We study theoretically the current-noise energy dependence for a N-N'-S structure, where N and S stand for bulk normal metal and superconductor, respectively, and N' for a short diffusive normal metal. Using quasiclassical theory of current fluctuations we obtain explicit expressions for the noise valid for arbitrary distributions of channel transparencies on both junctions. The differential Fano factor turns out to depend on both junction transparencies and the ratio of the two conductances. We conclude that measurement of differential conductance and noise can be used to probe the channel distribution of the interfaces.