Spin Gap and Resonance at the Nesting Wavevector in Superconducting FeSe0.4Te0.6

TL;DR

This study uses neutron scattering to investigate magnetic excitations in FeSe0.4Te0.6, revealing a spin resonance linked to s+/- superconductivity and Fermi surface nesting, providing insights into the magnetic properties of this superconductor.

Contribution

It demonstrates the presence of a spin resonance in FeSe0.4Te0.6 associated with s+/- pairing and Fermi surface nesting, advancing understanding of magnetic excitations in iron-based superconductors.

Findings

Low energy spin fluctuations at wave vector (0.5,0.5,L)

Development of a spin resonance at 6.5 meV in the superconducting state

Resonance consistent with a bound state related to s+/- superconductivity

Abstract

Neutron scattering is used to probe magnetic excitations in FeSe_{0.4}Te_{0.6} (T_c=14 K). Low energy spin fluctuations are found with a characteristic wave vector $(0.5,0.5,L)$ that corresponds to Fermi surface nesting and differs from Q_m=(\delta,0,0.5) for magnetic ordering in Fe_{1+y}Te. A spin resonance with \hbar\Omega_0=6.5 meV \approx 5.3 k_BT_c and \hbar\Gamma=1.25 meV develops in the superconducting state from a normal state continuum. We show that the resonance is consistent with a bound state associated with s+/- superconductivity and imperfect quasi-2D Fermi surface nesting.