Ferromagnetic Kitaev interaction and the origin of large magnetic anisotropy in α-RuCl3

• Published in: Nature physics 2020-08, Vol.16 (8), p.837-840
• Main Authors: Sears, Jennifer A., Chern, Li Ern, Kim, Subin, Bereciartua, Pablo J., Francoual, Sonia, Kim, Yong Baek, Kim, Young-June
• Format: Article
• Language: English
• Subjects: 639/766/119/997; 639/766/119/999; Anisotropy; Antiferromagnetism; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Elastic scattering; Ferromagnetism; Letter; Magnetic anisotropy; Magnetic permeability; Magnetic properties; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Ruthenium trichloride; Spin liquid; Theoretical; X-ray scattering
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-020-0874-0

α-RuCl 3 is drawing much attention as a promising candidate for the Kitaev quantum spin liquid 1 – 8 . However, despite intensive research efforts, controversy remains about the form of the basic interactions governing the physics of this material. Even the sign of the Kitaev interaction (the bond-dependent anisotropic interaction responsible for Kitaev physics) is still under debate, with conflicting results from theoretical and experimental studies 5 , 6 , 9 – 15 . The significance of the symmetric off-diagonal exchange interaction (referred to as the Γ term) is another contentious question 16 – 18 . Here, we present resonant elastic X-ray scattering data that provide unambiguous experimental constraints to the two leading terms in the magnetic interaction Hamiltonian. We show that the Kitaev interaction ( K ) is ferromagnetic, and that the Γ term is antiferromagnetic and comparable in size to the Kitaev interaction. Our findings also provide a natural explanation for the large anisotropy of the magnetic susceptibility in α-RuCl 3 as arising from the large Γ term. We therefore provide a crucial foundation for understanding the interactions underpinning the exotic magnetic behaviours observed in α-RuCl 3 . α-RuCl 3 is a promising candidate for realizing the Kitaev quantum spin liquid, but the physics governing its magnetic behaviour remain elusive. Resonant elastic X-ray scattering data now set unambiguous constraints on the leading terms in the Hamiltonian.