Unusual boundary effect on coherency of two-band superconductivity

TL;DR

This paper investigates how boundary effects uniquely influence the coherence lengths in two-band superconductors, revealing unusual temperature-dependent behaviors that impact proximity effects and critical temperature phenomena.

Contribution

It uncovers boundary-driven modifications in two-band superconductivity coherence lengths, including a singularity at a temperature below $T_c$, and explores their effects on proximity phenomena.

Findings

One coherence length diverges at $T_c$

Another shows a singularity at $T_{c+}<T_c$

Boundary effects modify the critical temperature behavior

Abstract

We demonstrate that the healing of two-band superconductivity near the surface of the system is governed by length scales which are drastically different from correlation lengths. Similar to the one-band case, one of the characteristic lengths diverges at critical temperature $T_c$, while another one shows unusual behaviour having singularity at $T_{c+}<T_c$. By moving away from the boundary, these scales approach coherence lengths in the bulk state, where the divergence at $T_{c+}$ is removed by arbitrary weak interband coupling. Such a boundary-driven modification in coherency affects proximity phenomenon. We show that critical temperature of binary NS system can exhibit an inflection near $T_{c+}$ as two-band superconducting layer becomes thinner.