Neutron Scattering Studies of spin excitations in hole-doped Ba0.67K0.33Fe2As2 superconductor

TL;DR

This study uses inelastic neutron scattering to explore spin excitations in Ba0.67K0.33Fe2As2, revealing complex superconducting gap structures and detailed magnetic behavior in both normal and superconducting states.

Contribution

It provides new insights into the momentum-space anisotropy and correlation lengths of spin excitations, challenging previous understanding of the superconducting gap structure.

Findings

Normal state spin excitations form elongated ellipses along QAFM.

Below Tc, spin excitations become isotropic and more correlated.

Resonance maintains momentum anisotropy across the transition.

Abstract

We report inelastic neutron scattering experiments on single crystals of superconducting Ba0.67K0.33Fe2As2 (Tc = 38 K). In addition to confirming the resonance previously found in powder samples, we find that spin excitations in the normal state form longitudinally elongated ellipses along the QAFM direction in momentum space, consistent with density functional theory predictions. On cooling below Tc, while the resonance preserves its momentum anisotropy as expected, spin excitations at energies below the resonance become essentially isotropic in the in-plane momentum space and dramatically increase their correlation length. These results suggest that the superconducting gap structures in Ba0.67Ka0.33Fe2As2 are more complicated than those suggested from angle resolved photoemission experiments.