Positive and negative Hanbury-Brown and Twiss correlations in normal metal-superconducting devices

TL;DR

This paper investigates Hanbury-Brown and Twiss correlations in a superconductor-normal metal device, revealing conditions under which positive or negative current noise correlations occur, influenced by bias, reflection, and disorder.

Contribution

It demonstrates the existence of positive fermionic correlations in a superconductor-normal metal system and analyzes how reflection and disorder affect these correlations.

Findings

Positive correlations can occur in the Andreev regime.

Bias beyond the gap favors fermionic correlations.

Disorder enhances positive noise correlations.

Abstract

In the light of the recent analogs of the Hanbury--Brown and Twiss experiments in mesoscopic beam splitters, negative current noise correlations are recalled to be the consequence of an exclusion principle. Here, positive (bosonic) correlations are shown to exist in a fermionic system, composed of a superconductor connected to two normal reservoirs. In the Andreev regime, the correlations can either be positive or negative depending on the reflection coefficient of the beam splitter. For biases beyond the gap, the transmission of quasiparticles favors fermionic correlations. The presence of disorder enhances positive noise correlations. Potential experimental applications are discussed.