Spin resonance peak in Fe-based superconductors with unequal gaps

Abstract

We study the spin resonance in the superconducting state of iron-based materials within multiband models with two unequal gaps, ΔL and ΔS, on different Fermi-surface pockets. We show that, due to the indirect nature of the gap entering the spin susceptibility at the nesting wave vector Q, the total gap Δ̃ in the bare susceptibility is determined by the sum of gaps on two different Fermi-surface sheets connected by Q. For the Fermi-surface geometry characteristic of most iron pnictides and chalcogenides, the indirect gap is either Δ̃=ΔL+ΔS or Δ̃=2ΔL. In the s++ state, spin excitations below Δ̃ are absent unless additional scattering mechanisms are assumed. The spin resonance appears in the s± superconducting state at frequency ωR≤Δ̃. Comparison with available inelastic neutron-scattering data confirms that what is seen is the true spin resonance and not a peak inherent to the s++ state.

Source-reported materials — not catalogue approval

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