Testing the sign-changing superconducting gap in iron-based superconductors with quasiparticle interference and neutron scattering

TL;DR

This paper uses quasiparticle interference and neutron scattering to analyze the superconducting gap structure in iron-based superconductors, providing a method to determine the sign-changing nature of the gaps.

Contribution

It introduces a combined spectroscopic approach to unambiguously identify the phase and sign structure of the superconducting gaps in iron-based superconductors.

Findings

QPI and INS spectra are correlated through scattering vectors and energy scales.

Both spectroscopies reveal the nodeless, isotropic nature of the gaps.

Results support the possibility of sign-changing d-wave pairing in iron-selenide superconductors.

Abstract

We present a phenomenological calculation of the quasiparticle-interference (QPI) pattern and inelastic Neutron scattering (INS) spectra in iron-pnictide and layered iron-selenide compounds by using materials specific band-structure and superconducting (SC) gap properties. As both the QPI and the INS spectra arise due to scattering of the Bogolyubov quasiaprticles, they exibit an one-to-one correspondence of the scattering vectors and the energy scales. We show that these two spectroscopies complement each other in such a way that a comparative study allows one to extract the quantitative and unambiguous information about the underlying pairing structure and the phase of the SC gap. Due to the nodeless and isotropic nature of the SC gaps, both the QPI and INS maps are concentrated at only two energies in pnictide (two SC gaps) and one energy in iron-selenide, while the associated scattering vectors q for scattering of sign-changing and same-sign of the SC gaps change between these spectroscopies. The results presented, particularly for newly iron-selenide compounds, can be used to test the nodeless d-wave pairing in this class of high temperature superconductors.