Two-band model of Raman scattering on iron pnictide superconductors

TL;DR

This paper models Raman scattering in iron-pnictide superconductors using a two-band approach, predicting symmetry-dependent intensities and excitation peaks, and compares different pairing symmetries with experimental data.

Contribution

It introduces a two-band model to analyze Raman scattering in iron pnictides, predicting symmetry effects and identifying compatible pairing symmetries with experimental observations.

Findings

$B_{1g}$ intensity weaker than $B_{2g}$ in normal state

Interband excitation peaks at specific frequencies in non-resonant regime

Extended $s$- and $d_{xy}$-wave pairings fit experimental $B_{2g}$ data

Abstract

Based on a two-band model, we study the electronic Raman scattering intensity in both normal and superconducting states of iron-pnictide superconductors. For the normal state, due to the match or mismatch of the symmetries between band hybridization and Raman vertex, it is predicted that overall $B_{1g}$ Raman intensity should be much weaker than that of the $B_{2g}$ channel. Moreover, in the non-resonant regime, there should exhibit a interband excitation peak at frequency $\omega\simeq 7.3 t_1 (6.8t_1)$ in the $B_{1g}$ ($B_{2g}$) channel. For the superconducting state, it is shown that $\beta$-band contributes most to the $B_{2g}$ Raman intensity as a result of multiple effects of Raman vertex, gap symmetry, and Fermi surface topology. Both extended $s$- and $d_{xy}$-wave pairings in the unfolded BZ can give a good description to the reported $B_{2g}$ Raman data [Muschler {\em et al.}, Phys. Rev. B. {\bf 80}, 180510 (2009).], while $d_{x^2-y^2}$-wave pairing in the unfolded BZ seems to be ruled out.