Frustrated magnetic interactions in FeSe

TL;DR

This paper investigates the magnetic interactions in FeSe, revealing highly frustrated exchange couplings that explain its tunable superconductivity and nematicity through neutron scattering measurements and theoretical modeling.

Contribution

It provides the first detailed characterization of the frustrated magnetic exchange interactions in FeSe using neutron scattering and Gaussian approximation modeling.

Findings

FeSe exhibits highly frustrated nearest- and next-nearest-neighbor exchange interactions.

The magnetic structure factor can be modeled with weak further neighbor interactions.

Results explain the tunable superconductivity and nematicity in FeSe.

Abstract

The structurally simplest high-temperature superconductor FeSe exhibits an intriguing superconducting nematic paramagnetic phase with unusual spin excitation spectra that are different from typical spin waves; thus, determining its effective magnetic exchange interactions is challenging. Here we report neutron scattering measurements of spin fluctuations of FeSe in the tetragonal paramagnetic phase. We show that the equal-time magnetic structure factor, $\mathcal{S}(\textbf{Q})$, can be effectively modeled using the self-consistent Gaussian approximation calculation with highly frustrated nearest-neighbor ($J_{1}$) and next-nearest-neighbor ($J_{2}$) exchange couplings, and very weak further neighbor exchange interaction. Our results elucidate the frustrated magnetism in FeSe, which provides a natural explanation for the highly tunable superconductivity and nematicity in FeSe and related materials.