Quasiparticle Interference in Fe-based Superconductors Based on a Five-Orbital Tight-Binding Model

TL;DR

This paper studies quasiparticle interference in Fe-based superconductors using a five-orbital model, showing that QPI signals can be explained by both s++ and s± pairing states and analyzing magnetic field effects.

Contribution

It provides a detailed numerical analysis of QPI in Fe-based superconductors, challenging the applicability of the octet model and explaining experimental observations with both pairing symmetries.

Findings

QPI signals around q2 can be explained by both s++ and s± states.

The extinction rule from cuprates does not apply to Fe-based superconductors.

Magnetic field effects on QPI are consistent with both pairing states.

Abstract

We investigate the quasiparticle interference (QPI) in Fe-based superconductors in both the $s_{++}$-wave and $s_{\pm}$-wave superconducting states on the basis of the five-orbital model. In the octet model for cuprate superconductors with $d_{x^2 - y^2}$-wave state, the QPI signal due to the impurity scattering at ${q} = {k}_i - {k}_j$ ($E = | \Delta ( {k}_i ) |$, $i = 1 \sim 8$) disappears when the gap functions at ${k}_i$ and ${k}_j$ have the same sign. However, we show that this extinction rule does not hold in Fe-based superconductors with fully-gapped $s$-wave state. The reason is that the resonance condition $E = | \Delta ( {k}_i ) |$ is not satisfied under the experimental condition for Fe-based superconductors. We perform the detailed numerical study of the QPI signal using the $T$-matrix approximation, and show that the experimentally observed QPI peak around ${q}_2 = ( \pi, 0 )$ can be explained on the basis of both the $s_{++}$-wave and $s_{\pm}$-wave states. Furthermore, we discuss the magnetic field dependence of the QPI by considering the Zeeman effect, and find that the field-induced suppression of the peak intensity around ${q}_2$ can also be explained in terms of both the $s_{++}$-wave and $s_{\pm}$-wave states.