Magnetic ground state of FeSe

TL;DR

This study reveals that FeSe exhibits both stripe and Néel spin fluctuations and acts as a nematic quantum-disordered paramagnet, providing insights into its magnetic ground state and its relation to high-temperature superconductivity.

Contribution

The paper demonstrates that FeSe hosts both stripe and Nél spin fluctuations and behaves as a nematic quantum-disordered paramagnet, a novel magnetic state among iron-based superconductors.

Findings

FeSe shows both stripe and Nél spin fluctuations at 110 K.

Spectral weight shifts from Nél to stripe fluctuations in the nematic phase.

FeSe's magnetic moment is ~60% larger than in BaFe2As2.

Abstract

Elucidating the nature of the magnetism of a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds of the cuprate and iron-pnictide superconductors exhibit N\'eel and stripe magnetic order, respectively. However, FeSe, the structurally simplest iron-based superconductor, shows nematic order (Ts = 90 K), but not magnetic order in the parent phase, and its magnetic ground state is intensely debated. Here, we report inelastic neutron-scattering experiments that reveal both stripe and N\'eel spin fluctuations over a wide energy range at 110 K. On entering the nematic phase, a substantial amount of spectral weight is transferred from the N\'eel to the stripe spin fluctuations. Moreover, the total fluctuating magnetic moment of FeSe is ~ 60% larger than that in the iron pnictide BaFe2As2. Our results suggest that FeSe is a novel S = 1 nematic quantum-disordered paramagnet interpolating between the N\'eel and stripe magnetic instabilities.