Positive noise cross-correlations in superconducting hybrids: Roles of interfaces and interactions

TL;DR

This paper investigates shot noise cross-correlations in superconductor-normal metal structures, revealing conditions under which positive correlations occur despite negative conductance, and discusses the influence of interactions in the leads.

Contribution

It provides a comprehensive analysis of noise cross-correlations at various interface transparencies using both scattering and Green's function methods, highlighting the role of interactions.

Findings

Positive noise cross-correlations can occur in highly transparent contacts.

Negative crossed conductance does not necessarily imply negative noise correlations.

Interactions in the leads can induce sign changes in noise cross-correlations.

Abstract

Shot noise cross-correlations in normal metal-superconductor-normal metal structures are discussed at arbitrary interface transparencies using both the scattering approach of Blonder, Tinkham and Klapwik and a microscopic Green's function approach. Surprisingly, negative crossed conductance in such set-ups [R. Melin and D. Feinberg, Phys. Rev. B 70, 174509 (2004)] does not preclude the possibility of positive noise cross-correlations for almost transparent contacts. We conclude with a phenomenological discussion of interactions in the one dimensional leads connected to the superconductor, which induce sign changes in the noise cross-correlations.