Unusual Relationship between Magnetism and Superconductivity in FeTe$_{0.5}$Se$_{0.5}$

TL;DR

This study investigates magnetic excitations in FeTe$_{0.5}$Se$_{0.5}$ using neutron scattering, revealing unusual behaviors of resonance and incommensurate fluctuations that challenge common assumptions about their role in superconductivity.

Contribution

The paper provides new insights into the distinct behaviors of magnetic excitations in FeTe$_{0.5}$Se$_{0.5}$, highlighting their different responses to doping and questioning their universal role in pairing mechanisms.

Findings

Resonance at (0.5, 0.5, 0) remains fixed with doping.

Incommensurate fluctuations shift position as doping varies.

Magnetic excitations do not necessarily follow a common behavior in pairing.

Abstract

We use neutron scattering, to study magnetic excitations in crystals near the ideal superconducting composition of FeTe$_{0.5}$Se$_{0.5}$. Two types of excitations are found, a resonance at (0.5, 0.5, 0) and incommensurate fluctuations on either side of this position. We show that the two sets of magnetic excitations behave differently with doping, with the resonance being fixed in position while the incommensurate excitations move as the doping is changed. These unusual results show that a common behavior of the low energy magnetic excitations is not necessary for pairing in these materials.