Unconventional Anisotropic s-Wave Superconducting Gaps of LiFeAs Iron-Pnictide Superconductor

TL;DR

This study uses high-resolution ARPES to reveal multiple nodeless, anisotropic superconducting gaps in LiFeAs, highlighting complex pairing interactions and momentum-dependent gap structures in this iron-pnictide superconductor.

Contribution

It provides detailed momentum-resolved measurements of superconducting gaps and their anisotropy in LiFeAs, offering new insights into its pairing mechanism.

Findings

Multiple nodeless SC gaps with varying 2D/kBTc ratios

Gap anisotropy up to ~30% with four-fold symmetry

Antiphase anisotropy between hole and electron Fermi surfaces

Abstract

We have performed high-resolution angle-resolved photoemission spectroscopy on Fe-based superconductor LiFeAs (Tc = 18 K). We reveal multiple nodeless superconducting (SC) gaps with 2D/kBTc ratios varying from 2.8 to 6.4, depending on the Fermi surface (FS). We also succeeded in directly observing a gap anisotropy along the FS with magnitude up to ~30 %. The anisotropy is four-fold symmetric with an antiphase between the hole and electron FSs, suggesting complex anisotropic interactions for the SC pairing. The observed momentum dependence of the SC gap offers an excellent opportunity to investigate the underlying pairing mechanism.