Inelastic neutron scattering study on the resonance mode in an optimally doped superconductor LaFeAsO$_{0.92}$F$_{0.08}$

TL;DR

This study uses inelastic neutron scattering to investigate the magnetic resonance mode in an optimally doped iron-based superconductor, revealing a magnetic origin of the resonance and its relation to superconducting properties.

Contribution

First observation of a magnetic resonance mode in LaFeAsO$_{0.92}$F$_{0.08}$, linking resonance energy to $T_c$ and supporting magnetic pairing mechanisms.

Findings

Resonance mode appears below $T_c$ at $E_{res}\sim13$ meV.

Resonance energy scales with $T_c$, consistent with other iron-based superconductors.

Resonance is of magnetic origin, not phononic.

Abstract

An optimally doped iron-based superconductor LaFeAsO$_{0.92}$F$_{0.08}$ with $T_c = 29$ K has been studied by inelastic powder neutron scattering. The magnetic excitation at $Q=1.15$ \AA$^{-1}$ is enhanced below $T_c$, leading to a peak at $E_{res}\sim13$ meV as the resonance mode, in addition to the formation of a gap at low energy below the crossover energy $\Delta_{c}\sim10 meV$. The peak energy at $Q=1.15$ \AA$^{-1}$ corresponds to $5.2 k_B T_c$ in good agreement with the other values of resonance mode observed in the various iron-based superconductors, even in the high-$T_c$ cuprates. Although the phonon density of states has a peak at the same energy as the resonance mode in the present superconductor, the $Q$-dependence is consistent with the resonance being of predominately magnetic origin.