Spin-wave excitations and superconducting resonant mode in Cs(x)Fe(2-y)Se2

TL;DR

This study uses neutron scattering to investigate spin excitations and a magnetic resonance in Cs0.8Fe1.9Se2, revealing features common to Fe-based superconductors and indicating spatial separation of magnetic and superconducting phases.

Contribution

It provides the first detailed neutron scattering analysis of Cs0.8Fe1.9Se2, identifying a superconducting magnetic resonance similar to other Fe-based superconductors.

Findings

Detection of a magnetic resonance at 11 meV below Tc

Presence of spin-wave excitations unaffected by superconductivity

Resonance is a common feature in Fe-based superconductors

Abstract

We report neutron inelastic scattering measurements on the normal and superconducting states of single-crystalline Cs0.8Fe1.9Se2. Consistent with previous measurements on Rb(x)Fe(2-y)Se2, we observe two distinct spin excitation signals: (i) spin-wave excitations characteristic of the block antiferromagnetic order found in insulating A(x)Fe(2-y)Se2 compounds, and (ii) a resonance-like magnetic peak localized in energy at 11 meV and at an in-plane wave vector of (0.25, 0.5). The resonance peak increases below Tc = 27 K, and has a similar absolute intensity to the resonance peaks observed in other Fe-based superconductors. The existence of a magnetic resonance in the spectrum of Rb(x)Fe(2-y)Se2 and now of Cs(x)Fe(2-y)Se2 suggests that this is a common feature of superconductivity in this family. The low energy spin-wave excitations in Cs0.8Fe1.9Se2 show no measurable response to superconductivity, consistent with the notion of spatially separate magnetic and superconducting phases.