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

Abstract

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 $2\Delta$ 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 $\Delta (\mathbf{k})=\Delta \cos \frac{k_x}{2}\cos \frac{k_y}{2}$ proposed by several groups.

5 pages, 3 figures, discussion on the vertex corrections is extended

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