Observation of a 1/3 Magnetisation Plateau Phase as Evidence for the Kitaev Interaction in a Honeycomb-Lattice Antiferromagnet

Abstract

Fractional magnetisation plateaus, in which the magnetisation is pinned at a fraction of its saturated value within a range of external magnetic field, are spectacular macroscopic manifestations of the collective quantum behaviours. One prominent example of the plateau phase is found in spin-1/2 triangular-lattice antiferromagnets featuring strong geometrical frustration, and is often interpreted as quantum-fluctuation-stabilised state in magnetic field via the "order-by-disorder" mechanism. Here, we observe an unprecedented 1/3 magnetisation plateau between 5.2 and 7.4 T at 2 K in a spin-1 antiferromagnet Na${}_3$Ni${}_2$BiO${}_6$ with a honeycomb lattice, where conventionally no geometrical frustration is anticipated. By carrying out elastic neutron scattering measurements, we propose the spin structure of the plateau phase to be an unusual partial spin-flop ferrimagnetic order, transitioning from the zigzag antiferromagnetic order in zero field. Our theoretical calculations show that the plateau phase is stabilised by the bond-anisotropic Kitaev interaction. These results provide a new paradigm for the exploration of rich quantum phases in frustrated magnets and exotic Kitaev physics in high-spin systems.

Submitted version, 10 pages, 5 figures. Final version has been published in Nature Physics

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• Emergent quantum Majorana metal from a chiral spin liquid
• Chiral spin state and nematic ferromagnet in the spin-1 Kitaev-$\Gamma$ model
• Successive topological phase transitions in two distinct spin-flop phases on the honeycomb lattice
• Interplay of Kitaev Interaction and Off-diagonal Exchanges: Exotic Phases and Quantum Phase Diagrams
• Magnetic properties of van der Waals layered single crystals DyOBr and SmOCl
• Low-energy spin dynamics in a Kitaev material Na3Ni2BiO6 investigated by NMR
• Recent progress in quantum spin liquids, fractional magnetization plateaus, and unconventional superconductivity in kagome lattices
• Magnetization process of a quasi-two-dimensional quantum magnet: Two-step symmetry restoration and dimensional reduction
• Disorder-induced spin excitation continuum and spin-glass ground state in the inverse spinel CuGa${}_2$O${}_4$
• Ligand-SOC enhanced $4f^5$ Kitaev antiferromagnet: Application to ${\mathrm{SmI}}_3$
• Stabilization of zigzag order in NiPS${}_3$ via positive biquadratic interaction
• Sizable Ligand-Mediated Bond-Dependent Interactions in a Spin-1 Triangular Antiferromagnet NiI${}_2$