Quasiparticle interference in Fe-based superconductors based on a five-orbital tight-binding model

Abstract

We investigate the quasiparticle interference (QPI) in Fe-based superconductors in both the ${s}_{++}$-wave and ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave superconducting states on the basis of the five-orbital model. In the octet model for cuprate superconductors with ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave state, the QPI signal due to the impurity scattering at $\mathbit{q}={\mathbit{k}}_{i}\ensuremath{-}{\mathbit{k}}_{j}$ ($E=|\mathrm{\ensuremath{\Delta}}({\mathbit{k}}_{i})|, i=1\ensuremath{-}8$) disappears when the gap functions at ${\mathbit{k}}_{i}$ and ${\mathbit{k}}_{j}$ 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 $E=|\mathrm{\ensuremath{\Delta}}({\mathbit{k}}_{i})|$ 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 ${\mathbit{q}}_{2}=(\ensuremath{\pi},0)$ can be explained on the basis of both the ${s}_{++}$-wave and ${s}_{\ifmmode\pm\else\textpm\fi{}}$-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 ${\mathbit{q}}_{2}$ can also be explained in terms of both the ${s}_{++}$-wave and ${s}_{\ifmmode\pm\else\textpm\fi{}}$-wave states.