Proximity fingerprint of s+- superconductivity

TL;DR

This paper proposes a simple experimental test using proximity effects in layered superconductors to definitively identify s+- pairing symmetry in iron-based superconductors by observing characteristic features in the density of states.

Contribution

It introduces a novel, straightforward method to detect s+- superconductivity through proximity effect measurements in superconductor heterostructures.

Findings

Presence of a peak in the s-wave density of states indicates aligned s+- gap.

A dip in the s-wave density of states indicates anti-aligned s+- gap.

Observation of these features confirms s+- pairing symmetry.

Abstract

We suggest a straightforward and unambiguous test to identify possible opposite signs of superconducting order parameter in different bands proposed for iron-based superconductors (s+- state). We consider proximity effect in a weakly coupled sandwich composed of a s+- superconductor and thin layer of s-wave superconductor. In such system the s-wave order parameter is coupled differently with different s+- gaps and it typically aligns with one of these gaps. This forces the other s+- gap to be anti-aligned with the s-wave gap. In such situation the aligned band induces a peak in the s-wave density of states (DoS), while the anti-aligned band induces a dip. Observation of such contact-induced negative feature in the s-wave DoS would provide a definite proof for s+- superconductivity.