Doubled Shot Noise In Disordered Normal-Metal-Superconductor Junctions

TL;DR

This paper derives a formula for shot-noise power in disordered normal-metal-superconductor junctions, revealing an enhancement due to Cooper-pair transport and the influence of scattering channels on noise levels.

Contribution

It introduces a scattering approach formula for shot-noise power in such junctions, accounting for arbitrary normal regions and disorder effects.

Findings

Shot-noise power is doubled compared to the normal state due to Cooper pairs.

Noise remains below Poisson level because of noiseless scattering channels.

Derived formula relates shot-noise to transmission eigenvalues.

Abstract

The low-frequency shot-noise power of a normal-metal-superconductor junction is studied for arbitrary normal region. Through a scattering approach, a formula is derived which expresses the shot-noise power in terms of the transmission eigenvalues of the normal region. The noise power divided by the current is enhanced by a factor two with respect to its normal-state value, due to Cooper-pair transport in the superconductor. For a disordered normal region, it is still smaller than the Poisson noise, as a consequence of noiseless open scattering channels.