Nodes in the gap function of LaFePO, the gap function of the Fe(Se,Te) systems, and the STM signature of the s(+/-) pairing

Abstract

We reiterate, in more details, our previous proposal of using quasiparticle 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± with nodes on electron Fermi surfaces. For Fe(Se,Te) system we found fully gapped s± 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.