Magnon-spinon dichotomy in the Kitaev hyperhoneycomb $\beta$-Li${}_2$IrO${}_3$

Abstract

The family of edge-sharing tri-coordinated iridates and ruthenates has emerged in recent years as a major platform for Kitaev spin liquid physics, where spins fractionalize into emergent magnetic fluxes and Majorana fermions with Dirac-like dispersions. While such exotic states are usually pre-empted by long-range magnetic order at low temperatures, signatures of Majorana fermions with long coherent times have been predicted to manifest at intermediate and higher energy scales, similar to the observation of spinons in quasi-1D spin chains. Here we present a Resonant Inelastic X-ray Scattering study of the magnetic excitations of the hyperhoneycomb iridate $\beta$-Li${}_2$IrO${}_3$ under a magnetic field with a record-high-resolution spectrometer. At low-temperatures, dispersing spin waves can be resolved around the predicted intertwined incommensurate spiral and field-induced zigzag orders, whose excitation energy reaches a maximum of 16meV. A 2T magnetic field softens the dispersion around $\mathbf{Q}=0$. The behavior of the spin waves under magnetic field is consistent with our semiclassical calculations for the ground state and the dynamical spin structure factor, which further predicts that the ensued intertwined uniform states remain robust up to very high fields (100 T). Most saliently, the low-energy magnon-like mode is superimposed by a broad continuum of excitations, centered around 35meV and extending up to 100meV. This high-energy continuum survives up to at least 300K -- well above the ordering temperature of 38K -- and gives evidence for pairs of long-lived Majorana fermions of the proximate Kitaev spin liquid.

8 pages, 4 figures

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Cited by in corpus (14)

• Beyond Kitaev physics in strong spin-orbit coupled magnets
• Kitaev magnetism through the prism of lithium iridate
• Nearly itinerant electronic groundstate in the intercalated honeycomb iridate Ag${}_3$LiIr${}_2$O${}_6$
• Temperature evolution of the phonon dynamics in the Kitaev spin liquid
• Thermal Hall Effect in the Kitaev-Heisenberg System with Spin-Phonon Coupling
• Nonlinear response of the Kitaev honeycomb lattice model in a weak magnetic field
• Magnetic Excitations and Interactions in the Kitaev Hyperhoneycomb Iridate $\beta$-Li${}_2$IrO${}_3$
• RIXS interferometry and the role of disorder in the quantum magnet Ba${}_3$Ti${}_{3-x}$Ir${}_x$O${}_9$
• Phonon Dynamics in the Generalized Kitaev Spin Liquid
• Ground-State Phase Diagram of the Kitaev-Heisenberg Model on a Three-dimensional Hyperhoneycomb Lattice
• Signatures of non-Loudon-Fleury Raman scattering in the Kitaev magnet $\beta$-Li${}_2$IrO${}_3$
• Spin-orbital-lattice entanglement in the ideal j=1/2 compound K${}_2$IrCl${}_6$
• Sound attenuation in the hyperhoneycomb Kitaev spin liquid
• Signatures of fractionalization in the optical phonons of hyperhoneycomb Kitaev magnet $\beta$-Li${}_2$IrO${}_3$