Doping dependence of the spin excitations in Fe-based superconductors Fe1+yTe1-xSex

TL;DR

This study investigates how doping levels in Fe-based superconductors affect low-energy spin excitations, revealing a correlation between spin resonance proximity to (1/2 1/2 0) and superconducting strength.

Contribution

It provides systematic inelastic neutron scattering data showing the evolution of spin excitations with doping and their relation to superconductivity in Fe1+yTe1-xSex.

Findings

Spin excitations evolve towards (1/2 1/2 0) with doping.

Superconducting samples show a strong spin resonance near (1/2 1/2 0).

Resonance is closer to (1/2 1/2 0) than the underlying excitations.

Abstract

The Fe1+yTe1-xSex series of materials is one of the prototype families of Fe-based superconductors. To provide further insight into these materials we present systematic inelastic neutron scattering measurements of the low energy spin excitations for x=0.27, 0.36, 0.40, 0.49. These measurements show an evolution of incommensurate spin excitations towards the (1/2 1/2 0) wave vector with doping. Concentrations (x=0.40 and 0.49) which exhibit the most robust superconducting properties have spin excitations closest to (1/2 1/2 0) and also exhibit a strong spin resonance in the spin excitation spectrum below Tc. The resonance signal appears to be closer to (1/2 1/2 0) than the underlying spin excitations. We discuss the possible relationship between superconductivity and spin excitations at the (1/2 1/2 0) wave vector and the role that interstitial Fe may play.