Temperature-dependent transformation of the magnetic excitation spectrum on approaching superconductivity in Fe1-x (Ni/Cu)x Te0.5 Se0.5

TL;DR

This study reveals temperature-dependent changes in magnetic excitation spectra in Fe-based superconductors, showing spectral reconstruction up to three times the critical temperature, indicating strong magnetic interactions near superconductivity.

Contribution

It uncovers a novel temperature-dependent transformation of magnetic excitations in Fe1-x (Ni/Cu)x Te0.5 Se0.5, extending understanding of magnetic behavior near superconductivity.

Findings

Magnetic dispersion changes from incommensurate to U-shaped at low temperatures.

Spectral reconstruction occurs up to approximately 3 times Tc.

Strong magnetic interactions are involved in the approach to superconductivity.

Abstract

Spin excitations are one of the top candidates for mediating electron pairing in unconventional superconductors. Their coupling to superconductivity is evident in a large number of systems, by the observation of an abrupt redistribution of magnetic spectral weight at the superconducting transition temperature, Tc, for energies comparable to the superconducting gap. Here we report inelastic neutron scattering measurements on Fe-based superconductors, Fe1-x (Ni/Cu)x Te0.5 Se0.5, that emphasize an additional signature. The overall shape of the low energy magnetic dispersion changes from two incommensurate vertical columns at T >> Tc to a distinctly different U-shaped dispersion at low temperature. Importantly, this spectral reconstruction is apparent for temperature up to ~3Tc. If the magnetic excitations are involved in the pairing mechanism, their surprising modification on the approach to Tc demonstrates that strong interactions are involved.