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arXiv · 2607.14893

Sizable Ligand-Mediated Bond-Dependent Interactions in a Spin-1 Triangular Antiferromagnet NiI$_2$

Hao Xu·Weiqin Zhu·Shufan Cheng·Yanyan Shangguan·Song Bao·Junbo Liao·Bo Zhang·Zihang Song·Shuai Dong·Maofeng Wu·Stanislav E. Nikitin·Travis J. Williams·Changsong Xu·Jinsheng Wen
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Abstract

The bond-dependent anisotropic Kitaev interactions are the key for the Kitaev model, which has attracted intense interest for its potential to host quantum-spin-liquid states and fractional excitations. However, experimental realizations of such interactions remain scarce. Here, we investigate the magnetic excitations of NiI$_2$, a van der Waals magnet with spin $S=1$. By combining inelastic neutron scattering, magnetization measurements, magnetic structure analysis, first-principles calculations, and linear-spin-wave simulations, we identify a minimal model that features substantial Kitaev and off-diagonal $\Gamma$ interactions, which together stabilize the canted magnetic ground state and open a gap in the spin-wave spectrum. Notably, these interactions arise from strong spin-orbit coupling on the ligand ions, despite the quenched orbital moment of the magnetic Ni$^{2+}$ ions. Our results provide compelling experimental evidence for the ligand-driven Kitaev mechanism. This demonstrates a concrete pathway to generating strong bond-dependent anisotropy in systems where the magnetic ions themselves have weak spin-orbit coupling, thereby substantially broadening the range of potential Kitaev materials.

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Hao Xu, Weiqin Zhu, Shufan Cheng, Yanyan Shangguan, Song Bao, Junbo Liao, Bo Zhang, Zihang Song, Shuai Dong, Maofeng Wu, Stanislav E. Nikitin, Travis J. Williams, Changsong Xu, Jinsheng Wen. 2026-07-16. Sizable Ligand-Mediated Bond-Dependent Interactions in a Spin-1 Triangular Antiferromagnet NiI$_2$. https://doi.org/10.1103/7rr7-8cxr

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