Magnetic excitations of Fe_{1+y}Se_xTe_{1-x} in magnetic and superconductive phases

TL;DR

This study compares magnetic excitations in superconducting and non-superconducting FeSeTe crystals, revealing a spin resonance in the superconductor and incommensurate magnetic excitations in the non-superconductor, with magnetic correlations persisting above transition temperatures.

Contribution

It provides the first direct comparison of magnetic excitations in superconducting and non-superconducting FeSeTe, highlighting differences related to superconductivity.

Findings

Spin resonance at 7 meV in superconducting FeSeTe

Incommensurate magnetic excitations in non-superconducting FeSeTe

Magnetic correlations are quasi-two-dimensional and persist above transition temperatures

Abstract

We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe1.01Se0.50Te0.50 and non-superconducting Fe1.10Se0.25Te0.75. We confirm the existence of a spin resonance in the superconducting phase of Fe1.01Se0.50Te0.50, at an energy of 7 meV and a wavevector of (1/2,1/2,0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2,1/2,0)\pm(0.18,-0.18,0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low-energy magnetic excitation is also observed in Fe1.10Se0.25Te0.75 close to the commensurate antiferromagnetic ordering wavevector (1/2-\delta,0,1/2) where \delta \approx 0.03. The magnetic correlations in both samples are found to be quasi-two dimensional in character and persist well above the magnetic (Fe1.10Se0.25Te0.75) and superconducting (Fe1.01Se0.50Te0.50) transition temperatures.