Theory of Raman response in a superconductor with extended s-wave symmetry: Application to Fe-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 has a true resonance peak below $2\mathrm{\Delta }$ for extended s-wave superconducting gap, $\Delta($\mathbf{k}$) = \Delta (\cos k_x

• \cos k_y)/2$ in the folded Brillouin zone. No such peak emerges for a pure s-wave gap, a d-wave gap, and another extended s-wave gap with $\mathrm{\Delta }(\mathbf{k})=\mathrm{\Delta }\cos \frac{k_x}{2}\cos \frac{k_y}{2}$ proposed by several groups.