Frustrated spin order and stripe fluctuations in FeSe

TL;DR

This study combines Raman scattering experiments and theoretical simulations to reveal persistent frustrated stripe spin order and fluctuations in FeSe, a simple iron-based superconductor, shedding light on its unconventional magnetic properties.

Contribution

It provides the first combined experimental and theoretical evidence for nearly frustrated stripe magnetic order in FeSe.

Findings

Persistent low energy spin excitation peak near 500cm$^{-1}$

Softening of spin excitations around 100 K

Evidence for nearly frustrated stripe order in FeSe

Abstract

The charge and spin dynamics of the structurally simplest iron-based superconductor, FeSe, may hold the key to understanding the physics of high temperature superconductors in general. Unlike the iron pnictides, FeSe lacks long range magnetic order in spite of a similar structural transition around 90\,K. Here, we report results of Raman scattering experiments as a function of temperature and polarization and simulations based on exact diagonalization of a frustrated spin model. Both experiment and theory find a persistent low energy peak close to 500cm$^{-1}$ in $B_{1g}$ symmetry, which softens slightly around 100\,K, that we assign to spin excitations. By comparing with results from neutron scattering, this study provides evidence for nearly frustrated stripe order in FeSe.