Detecting sign-changing superconducting gap in LiFeAs using quasiparticle interference

TL;DR

This paper uses a realistic tight-binding model and quasiparticle interference analysis to detect sign changes in the superconducting gap of LiFeAs, confirming previous simple model results and discussing the challenges in identifying complex gap structures.

Contribution

It demonstrates that quasiparticle interference features can reveal gap sign changes in a realistic model of LiFeAs, extending prior simplified models.

Findings

QPI features consistent with $s_{+-}$-wave gap in realistic model

Difficulty in identifying complex gap sign structures due to small pockets

Confirmation of previous simple model results

Abstract

Using a realistic ten-orbital tight-binding model Hamiltonian fitted to the angle-resolved photoemission (ARPES) data on LiFeAs, we analyze the temperature, frequency, and momentum dependencies of quasiparticle interference (QPI) to identify gap sign changes in a qualitative way, following our original proposal [Phys. Rev. B 92, 184513 (2015)]. We show that all features present for the simple two-band model for the sign-changing $s_{+-}$-wave superconducting gap employed previously are still present in the realistic tight-binding approximation and gap values observed experimentally. We discuss various superconducting gap structures proposed for LiFeAs, and identify various features of these superconducting gaps functions in the quasiparticle interference patterns. On the other hand, we show that it will be difficult to identify the more complicated possible sign structures of the hole pocket gaps in LiFeAs, due to the smallness of the pockets and the near proximity of two of the gap energies.