Self-energy driven resonance-like inelastic neutron spectrum in $s_{++}$-wave state in Fe-based superconductors

Abstract

To elucidate the pairing states in Fe-based superconductors, we perform careful calculation of the dynamical spin susceptibility ${\chi }^S(q,\omega )$ at very low temperatures ($T\sim 1$ meV). The feedback effect on both the self-energy and ${\chi }^S(q,\omega )$ from the superconducting gap are self-consistently analyzed based on the fluctuation-exchange (FLEX) approximation. In the $s_{+-}$-wave state, which has sign-reversal in the gap function, ${\chi }^S(q,\omega )$ at the nesting momentum $q=Q$ shows a resonance peak even when the system is away from the magnetic quantum-critical-point (QCP). In the $s_{++}$-wave state that has no sign-reversal, ${\chi }^S(q,\omega )$ shows a large hump structure when the system is close to the magnetic QCP. This result confirms the validity of self-energy driven resonance-like peak in $s_{++}$-wave state proposed in our previous semi-microscopic study: The enhancement in ${\chi }^S(q,\omega )$ due to self-energy effect exceeds the suppression due to coherence factor effect near magnetic QCP. We stress that the hump structure in the $s_{++}$-wave state given by the FLEX method smoothly changes to resonance-like sharp peak structure as the system approaches magnetic QCP, which was not reported in our previous studies. The obtained $\omega$- and $T$-dependences of ${\chi }^S(q,\omega )$ in the $s_{++}$-wave state resemble to the resonance-like feature in inelastic neutron scattering spectra recently observed in Na(Fe,Co)As and FeSe

11 pages, 14 figures, Apprndix B has been added

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Cited by in corpus (4)

• Neutron spin resonance in a quasi-two-dimensional iron-based superconductor
• Unconventional density waves and superconductivities in Fe-based superconductors and other strongly correlated electron systems
• Efficient fluctuation exchange approach to low-temperature spin fluctuations and superconductivity: from the Hubbard model to Na${}_x$CoO${}_2\cdot y$H${}_2$O
• Possible pairing symmetry in the FeSe-based superconductors determined by quasiparticle interference