Nodes in the Gap Function of LaFePO, the Gap Function of the Fe(Se,Te) Systems, and the STM Signature of the s$_{\pm}$ Pairing

TL;DR

This paper uses functional renormalization group analysis and quasi-particle interference to investigate the pairing symmetry in iron-based superconductors, revealing nodal and fully gapped s$_{ ext{±}}$ states with orbital-dependent gap features.

Contribution

It provides detailed FRG results on LaFePO and Fe(Se,Te) superconductors, identifying their pairing symmetries and orbital characteristics, and connects these to experimental signatures.

Findings

LaFePO exhibits nodal s$_{ ext{±}}$ pairing with nodes on electron Fermi surfaces.

Fe(Se,Te) shows fully gapped s$_{ ext{±}}$ pairing with anisotropic gaps.

Orbital analysis reveals large gaps concentrated in regions with $xy$ orbital character.

Abstract

We reiterate, in more details, our previous proposal of using quasi-particle interference to determine the pairing form factor in iron-based superconductors. We also present our functional renormalization group(FRG) results on LaFePO and Fe(Se,Te) superconductors. In particular we found that the leading pairing channel in LaFePO is nodal s$_{\pm}$, with nodes on electron Fermi surfaces. For Fe(Se,Te) system we found fully gapped s$_{\pm}$ pairing, with substantial gap anisotropy on electron Fermi surfaces, and large gap is concentrated in regions with dominant $xy$ orbital character. We further fit the form factor obtained by FRG to real space orbital basis pairing picture, which shows more clearly the differences between different iron-based superconductors.