Distinct Modulation Behavior of Superconducting Coherence Peaks Associated with Sign-Reversal Gaps in FeTe$_{0.55}$Se$_{0.45}$

TL;DR

This study uses scanning tunneling microscopy to identify two types of superconducting gap modulations in FeTe$_{0.55}$Se$_{0.45}$, revealing that pair-breaking scattering interference explains the observed phenomena and advances understanding of impurity effects in iron-based superconductors.

Contribution

The paper demonstrates that pair-breaking scattering interference is the primary mechanism for superconducting gap modulations in FeTe$_{0.55}$Se$_{0.45}$, distinguishing it from other theories.

Findings

Identification of in-phase and anti-phase gap modulations.

Correlation of modulations with sign-reversing and sign-preserving scattering.

Evidence supporting PBSI as the dominant mechanism.

Abstract

Using high-resolution scanning tunneling microscopy, we reveal two distinct types of superconducting (SC) gap modulations in bulk superconductor FeTe$_{0.55}$Se$_{0.45}$. By analyzing the phase relation between modulations at positive and negative bias, we identify in-phase (particle-hole asymmetric) and anti-phase (particle-hole symmetric) oscillations, corresponding to sign-reversing and sign-preserving scattering processes, respectively. The observed features are consistent with predictions from pair-breaking scattering interference (PBSI) theory and are distinguishable from other alternative mechanisms such as pair density waves. Our results provide compelling evidence that PBSI is the dominant mechanism behind the SC gap modulations in FeTe$_{0.55}$Se$_{0.45}$, offering new insights into the role of impurity scattering in iron-based superconductors.