Theoretical approach to resonant inelastic x-ray scattering in iron-based superconductors at the energy scale of the superconducting gap.

Pasquale Marra,Steffen Sykora,Jeroen Van Den Brink

doi:10.1038/srep25386

Abstract

We develop a phenomenological theory to predict the characteristic features of the momentum-dependent scattering amplitude in resonant inelastic x-ray scattering (RIXS) at the energy scale of the superconducting gap in iron-based super-conductors. Taking into account all relevant orbital states as well as their specific content along the Fermi surface we evaluate the charge and spin dynamical structure factors for the compounds LaOFeAs and LiFeAs, based on tight-binding models which are fully consistent with recent angle-resolved photoemission spectroscopy (ARPES) data. We find a characteristic intensity redistribution between charge and spin dynamical structure factors which discriminates between sign-reversing and sign-preserving quasiparticle excitations. Consequently, our results show that RIXS spectra can distinguish between s± and s++ wave gap functions in the singlet pairing case. In addition, we find that an analogous intensity redistribution at small momenta can reveal the presence of a chiral p-wave triplet pairing.

Highlights

The experimental side, inelastic neutron scattering (INS) experiments[35] seem consistent with the presence of spin-singlet pairing with s-wave symmetry, whereas scanning tunneling microscopy (STM) experiments of the quasiparticle interference[36] indicate a p-wave spin-triplet state or a singlet pairing mechanism with a more complex order parameter (s + id wave)
We have shown that RIXS is sensitive to phase and orbital symmetry of SC order parameter, and can be used as an additional experimental method to probe the nature of the SC pairing[42]
In order to present in the most clear way how to distinguish between the different pairing scenarios in LiFeAs, we show in Fig. 5 the RIXS spectra as a function of the energy loss for the charge and spin dynamical structure factor (DSF) of quasiparticle excitations at QAF and at (π/2), again for different choices of the SC order parameter symmetry

Summary

Introduction

The experimental side, INS experiments[35] seem consistent with the presence of spin-singlet pairing with s-wave symmetry, whereas STM experiments of the quasiparticle interference[36] indicate a p-wave spin-triplet state or a singlet pairing mechanism with a more complex order parameter (s + id wave). We study in this paper the charge and spin DSF for iron-based superconductors using accepted band structure models, and comparing different pairing mechanisms and order parameter symmetries.

Results

Conclusion