I-V characteristics of SNS junctions with a multivalley normal region

TL;DR

This paper investigates how long inter-valley and inelastic relaxation times in multivalley conductors dramatically influence the I-V characteristics of SNS junctions, revealing nonmonotonic behavior and significant resistance variations.

Contribution

It generalizes the Larkin-Ovchinnikov equations to multivalley superconductors and provides a kinetic description of multivalley SNS junctions, highlighting unique I-V features.

Findings

I(V) is nonmonotonic with two peaks at specific voltages.

The nonlinear resistance can be much smaller than the normal state resistance.

Long relaxation times dominate the junction's electrical response.

Abstract

In multivalley conductors the inter-valley relaxation time $\tau_v$ and the inelastic relaxation time $\tau_{in}$ may be significantly longer than the intra-valley momentum relaxation time $\tau$. We show that this separation of time scales has dramatic effects on the I-V characteristics of SNS junctions with a multivalley normal region. We generalize the Larkin-Ovchinnikov equations describing superconducting kinetics to the case of multivalley superconductors. We use this generalization to obtain a kinetic description of multivalley SNS junctions. We find that at constant voltage bias $V$, the current $I(V)$ is nonmonotonic; it exhibits two peaks of similar magnitude $I_\text{max,1} \sim I_\text{max,2}$ at $V_1 \sim \hbar(e\tau_{in})^{-1}$ and $V_2\sim \hbar(e\tau_v)^{-1}$, which may greatly exceed the critical current $I_c(T)$. At constant current bias $I$ we find that in a wide interval, $I_c(T) < I \lesssim I_{\text{jump}}$, the nonlinear resistance of the junction is controlled by the long relaxation times and may be several orders of magnitude smaller than the normal state resistance.