Nonequilibrium phenomena in multiple normal-superconducting tunnel heterostructures

TL;DR

This paper explores nonequilibrium effects in a mesoscopic NISINISIN heterostructure, revealing how bias voltage can induce electron cooling or complex energy distributions, affecting superconducting gaps.

Contribution

It introduces a detailed nonequilibrium theoretical analysis of NISINISIN heterostructures, showing how biasing influences electron distributions and superconducting properties.

Findings

Bias voltage drives the central N island far from equilibrium.

Energy distributions can have multiple peaks at multiples of the superconducting chemical potential.

Superconducting gap is suppressed under strong nonequilibrium conditions.

Abstract

Using the nonequilibrium theory of superconductivity with the tunnel Hamiltonian, we consider a mesoscopic NISINISIN heterostructure, i.e., a structure consisting of five intermittent normal-metal (N) and superconducting (S) regions separated by insulating tunnel barriers (I). Applying the bias voltage between the outer normal electrodes one can drive the central N island very far from equilibrium. Depending on the resistance ratio of outer and inner tunnel junctions, one can realize either effective electron cooling in the central N island or create highly nonequilibrium energy distributions of electrons in both S and N islands. These distributions exhibit multiple peaks at a distance of integer multiples of the superconducting chemical potential. In the latter case the superconducting gap in the S islands is strongly suppressed as compared to its equilibrium value.