Evidence for local moment magnetism in superconducting FeTe0.35Se0.65

TL;DR

This study provides evidence of local moment magnetism in FeTe0.35Se0.65, showing persistent magnetic moments across a wide temperature range, challenging purely itinerant electron models of magnetism in this superconductor.

Contribution

The paper demonstrates the presence of substantial local magnetic moments in FeTe0.35Se0.65, indicating local moment behavior coexists with superconductivity, which is a novel insight into its magnetic properties.

Findings

Substantial magnetic moment (~0.26 μB/Fe) persists from below T_c to 300 K.

Magnetic spectral weight remains largely unchanged with temperature.

States far from the Fermi energy contribute to local spin polarization.

Abstract

The nature of the magnetic correlations in Fe-based superconductors remains a matter of controversy. To address this issue, we use inelastic neutron scattering to characterize the strength and temperature dependence of low-energy spin fluctuations in FeTe$_{0.35}$Se$_{0.65}$ ($T_c \sim 14$ K). Integrating magnetic spectral weight for energies up to 12 meV, we find a substantial moment ($\agt 0.26 \mu_B/$Fe) that shows little change with temperature, from below T$_c$ to 300 K. Such behavior cannot be explained by the response of conduction electrons alone; states much farther from the Fermi energy must have an instantaneous local spin polarization. It raises interesting questions regarding the formation of the spin gap and resonance peak in the superconducting state.