Proximate ferromagnetic state in the Kitaev model material \u03b1-RuCl3

H Suzuki,M Minola,H Gretarsson,B Keimer,B J Kim,Lichen Wang ,Jiří Chaloupka ,Heonoh Kim ,Kentaro Ueda ,Daniel Weber ,Huimei Liu ,Maria Daghofer ,Hasan Yavaş ,Joel Bertinshaw ,Giniyat Khaliullin ,Katrin Fürsich ,Hideo Takahashi ,Bettina V Lotsch ,Zichen Yang ,Sourav Laha

doi:10.1038/s41467-021-24722-4

Abstract

α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. We have quantified the spin Hamiltonian of α-RuCl3 by a resonant inelastic x-ray scattering study at the Ru L3 absorption edge. In the paramagnetic state, the quasi-elastic intensity of magnetic excitations has a broad maximum around the zone center without any local maxima at the zigzag magnetic Bragg wavevectors. This finding implies that the zigzag order is fragile and readily destabilized by competing ferromagnetic correlations. The classical ground state of the experimentally determined Hamiltonian is actually ferromagnetic. The zigzag state is stabilized by quantum fluctuations, leaving ferromagnetism – along with the Kitaev spin liquid – as energetically proximate metastable states. The three closely competing states and their collective excitations hold the key to the theoretical understanding of the unusual properties of α-RuCl3 in magnetic fields.

Highlights

Α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model
The elementary excitations in the presence of a magnetic field are represented by emergent non-abelian anyons, which could serve as a key element in topological quantum computation
The bond-directional magnetic interactions of the Kitaev model can be realized in strongly correlated transition metal compounds, where spin–orbit entangled pseudospins eS 1⁄4 1=2 are arranged on a honeycomb lattice of edgeshared octahedra[4,5]

Summary

Introduction

Α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. Comparison with exact-diagonalization calculations of the RIXS intensity yields the hierarchy of interaction parameters between the pseudospins and reveals their individual roles: (1) the ferromagnetic (FM) Kitaev coupling K = −5.0 meV is dominant, (2) the FM Heisenberg interaction J = −3.0 meV enhances the FM correlations and renders the zigzag order fragile, (3) the off-diagonal interaction Γ = 2.5 meV stabilizes the zigzag order at low temperatures and explains the magnetic moment direction.

Results

Conclusion