# Spin excitations and the Fermi surface of superconducting FeS

## TL;DR

This study investigates the magnetic and electronic properties of superconducting FeS, revealing it as a less correlated tetragonal paramagnet without nematic order, and clarifying the relationship between spin excitations and superconductivity.

## Contribution

The paper provides the first comprehensive measurements showing FeS lacks nematic order and has reduced quasiparticle mass compared to FeSe, clarifying its magnetic excitations and their relation to superconductivity.

## Key findings

- FeS is a tetragonal paramagnet without nematic order.
- FeS exhibits only stripe-type spin excitations up to 100 meV.
- No direct coupling between spin excitations and superconductivity in FeS.

## Abstract

High-temperature superconductivity occurs near antiferromagnetic instabilities and nematic state. Debate remains on the origin of nematic order in FeSe and its relation with superconductivity. Here, we use transport, neutron scatter- ing and Fermi surface measurements to demonstrate that hydro-thermo grown superconducting FeS, an isostructure of FeSe, is a tetragonal paramagnet without nematic order and with a quasiparticle mass significantly reduced from that of FeSe. Only stripe-type spin excitation is observed up to 100 meV. No direct coupling between spin excitation and superconductivity in FeS is found, suggesting that FeS is less correlated and the nematic order in FeSe is due to competing checkerboard and stripe spin fluctuations.