Shot Noise and Proximity Effect in Superconductor--Normal-Metal Heterostructures

TL;DR

This paper investigates current noise and correlations in superconductor-normal-metal heterostructures, revealing reentrant shot noise behavior and positive cross-correlations, advancing understanding of mesoscopic transport phenomena.

Contribution

It introduces a comprehensive Keldysh-Green's function approach to analyze shot noise and correlations, highlighting the reentrant behavior and positive cross-correlations in these heterostructures.

Findings

Shot noise exhibits reentrant behavior similar to conductance.

Effective charge is suppressed below 2e at intermediate energies.

Positive cross-correlations are a common feature in multi-terminal structures.

Abstract

Current noise provides useful information on correlations important for transport properties of mesoscopic systems. Of particular interest, both experimentally and theoretically, are heterostructures of normal metals and superconductors. We use an extended Keldysh-Green's function approach to calculate the current correlations fully accounting for the superconducting proximity effect. The shot noise in diffusive wires shows a reentrant behaviour, similar to the reentrance effect of the conductance. At intermediate energies the effective charge (the ratio of the differential noise and differential conductance) is suppressed below the value of the Cooper pair charge 2e due to higher correlations. In superconducting heterostructures with more than two normal leads, we address the question of the sign of correlations between currents in different terminals. We show that positive crosscorrelations are a generic feature in these structures, which should be easily observable experimentally.