Robust determination of superconducting gap sign changes via quasiparticle interference

TL;DR

This paper proposes a temperature-dependent analysis of quasiparticle interference data to qualitatively identify gap sign changes in superconductors, providing a model-independent approach for Fe-based materials.

Contribution

It introduces a novel, qualitative method using temperature dependence of QPI data to detect superconducting gap sign changes, applicable to Fe-based superconductors.

Findings

Temperature dependence of QPI can reveal gap sign changes.

Method applied successfully to $s_{ ext{±}}$ and $s_{++}$ states.

Provides a model-independent way to analyze superconducting gap structure.

Abstract

Phase-sensitive measurements of the superconducting gap in Fe-based superconductors have proven more difficult than originally anticipated. While quasiparticle interference (QPI) measurements based on scanning tunneling spectroscopy are often proposed as defnitive tests of gap structure, the analysis typically relies on details of the model employed. Here we point out that the temperature dependence of momentum-integrated QPI data can be used to identify gap sign changes in a qualitative way, and present an illustration for $s_{\pm}$ and $s_{++}$ states in a system with typical Fe-pnictide Fermi surface.