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

TL;DR

This study uses inelastic neutron scattering to investigate low-energy spin excitations in the superconductor (Li0.8Fe0.2)ODFeSe, revealing temperature-dependent magnetic responses and potential crossover between pairing symmetries.

Contribution

First detailed inelastic neutron scattering analysis of (Li0.8Fe0.2)ODFeSe revealing spin excitations and their relation to superconductivity and pairing symmetry.

Findings

Spin excitations are observed near specific wave vectors consistent with Fermi surface nesting.

Magnetic response below 2Δ_SC shows an abrupt enhancement below T_c, indicating a spin resonance.

High-energy response increases gradually with weak anomaly at T_c.

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.