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

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.