Inhomogeneous state in non-equilibrium superconductor/normal metal tunnel structures: a LOFF-like phase for non-magnetic systems

TL;DR

This paper investigates non-equilibrium states in superconductor-normal metal tunnel structures, revealing inhomogeneous phases analogous to LOFF states, characterized by nonuniform current and temperature distributions due to instability in the uniform state.

Contribution

It introduces a model for non-equilibrium in NSN structures showing inhomogeneous states similar to LOFF phases in non-magnetic systems, expanding understanding of nonuniform superconducting states.

Findings

I-V characteristics can be S-shaped.

Nonuniform current and temperature distributions arise.

Instability of uniform states leads to inhomogeneous phases.

Abstract

We analyze non-equilibrium states in a tunnel superconductor-normal metal (NSN) structure in the presence of a tunnel current $I$. We use an approximation of an effective temperature $T$ and calculate the current-voltage I-V characteristics. It is shown that the I-V dependence may have an S-shaped form. We determine nonuniform current $I(x)$ and temperature $T(x)$ distributions that arise as a result of instability of the uniform state with negative differential conductance ($dI/dV<0$). We discuss an analogy with equilibrium superconductors with an exchange field in which nonuniform states predicted by Larkin-Ovchinnikov and Fulde-Ferrel are possible.