The Saga of $\alpha$-RuCl${}_3$: Parameters, Models, and Phase Diagrams

Abstract

RuCl${}_3$ was likely the first ever deliberately synthesized ruthenium compound, following the discovery of the ${}_{44}$Ru element in 1844. For a long time it was known as an oxidation catalyst, with its physical properties being discrepant and confusing, until a decade ago when its allotropic form $\alpha$-RuCl${}_3$ rose to exceptional prominence. This "re-discovery" of $\alpha$-RuCl${}_3$ has not only reshaped the hunt for a material manifestation of the Kitaev spin liquid, but it has opened the floodgates of theoretical and experimental research in the many unusual phases and excitations that the anisotropic-exchange magnets as a class of compounds have to offer. Given its importance for the field of Kitaev materials, it is astonishing that the low-energy spin model that describes this compound and its possible proximity to the much-desired spin-liquid state is still a subject of significant debate ten years later. In the present study, we argue that the existing key phenomenological observations put strong natural constraints on the effective microscopic spin model of $\alpha$-RuCl${}_3$, and specifically on its spin-orbit-induced anisotropic-exchange parameters that are responsible for the non-trivial physical properties of this material. These constraints allow one to focus on the relevant region of the multi-dimensional phase diagram of the $\alpha$-RuCl${}_3$ model, suggest an intuitive description of it via a different parametrization of the exchange matrix, offer a unifying view on the earlier assessments of its parameters, and bring closer together several approaches to the derivation of anisotropic-exchange models. We explore extended phase diagrams relevant to the $\alpha$-RuCl${}_3$ parameter space using quasi-classical, Luttinger-Tisza, exact diagonalization, and density-matrix renormalization group methods, demonstrating a remarkably c... (arxiv cutoff; for the rest, see the paper)

39 pages, 28 Figures. Text of immense pedagogical power. Published under different title. Winner of the PRB beauty award (Editor's Suggestion)

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Cited by in corpus (8)

• Ferrimagnetism from quantum fluctuations in Kitaev materials
• Topological Majorana flat bands in the Kitaev model on a Bishamon-kikko lattice
• Magnetostriction in the $J$-$K$-$\Gamma$ model: Application of the numerical linked cluster expansion
• Magnetic excitations in the Kitaev material Na${}_2$IrO${}_3$ studied by neutron scattering
• An integrated theoretical and numerical approach to understand modern experiments on quantum magnetism
• Spin sensitive transport in RuCl_3/Pt heterostructures: revealing a field-transverse spin anisotropy in a spin liquid candidate
• Dynamical Response of the Kitaev Spin Liquid under Third-Nearest-Neighbor Heisenberg Interaction
• Thermal and quantum fluctuations in extended Kitaev-Yao-Lee spin-orbital model