Theory of Raman response of a superconductor with extended s-wave symmetry: Application to the iron pnictides

We argue that Raman study of Fe-pnictides is a way to unambiguously distinguish between various superconducting gaps proposed for these materials. We show that A(1g) Raman intensity develops a true resonance peak below 2 Delta if the pairing gap has A(1g) symmetry in the folded Brillouin zone (Delta(k=0)=Delta, Delta(pi, pi)=-Delta). No such peak develops for a pure s-wave gap, a d-wave gap, and an extended s-wave gap with Delta(k) =Delta cosk(x)/2cosk(y)/2. We show that the peak remains quite strong for the values of interpocket impurity scattering used to fit NMR data.