Low-energy spin excitations in Li(0.8)Fe(0.2)ODFeSe superconductor studied with inelastic neutron scattering

Abstract

We report an inelastic neutron scattering study of single crystals of (Li${}_{0.8}$Fe${}_{0.2}$)ODFeSe. Temperature-dependent low-energy spin excitations are observed near $\mathbf{Q}=$ (0.5, 0.27, 0.5) and equivalent wave vectors symmetrically surrounding $\mathbf{Q}=$ (0.5, 0.5, 0.5) in the 1-Fe Brillouin zone, consistent with a Fermi-surface-nesting description. The excitations are broadly distributed in energy, ranging from 16 to 35 meV. Upon cooling below the superconducting critical temperature ($T_{\mathrm{c}}$), magnetic response below twice the superconducting gap $2{\Delta }_{\mathrm{SC}}$ exhibits an abrupt enhancement, consistent with the notion of spin resonance, whereas the response at higher energies increases more gradually with only a weak anomaly at $T_{\mathrm{c}}$. Our results suggest that (Li${}_{0.8}$Fe${}_{0.2}$)ODFeSe might be on the verge of a crossover between different Cooper-pairing channels with distinct symmetries.

5 pages, 4 figures

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