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arXiv · 2403.14754

Transforming from Kitaev to Disguised Ising Chain: Application to CoNb$_2$O$_6$

Derek Churchill·Hae-Young Kee
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Abstract

For many years, CoNb$_2$O$_6$ has served as an exemplar of the one-dimensional Ising model. However, recent experimental and theoretical analyses challenge its applicability to this material. Prior to that, a tailored spin model for 3d$^7$ systems such as Co$^{2+}$, known as the $JK\Gamma$ model, has emerged, featuring Heisenberg $(J)$, Kitaev $(K)$, and Gamma $(\Gamma)$ interactions. While these interactions are permitted by the symmetry of the system, their role in CoNb$_2$O$_6$ remains enigmatic. We present a microscopic theory based on spin-orbit entangled J$_{\textrm{eff}}$ = 1/2 states, aimed at elucidating the roles of Kitaev and Gamma interactions in shaping Ising anisotropy. Leveraging strong coupling theory, we identify a dominant ferromagnetic Kitaev interaction. Furthermore, by comparing dynamical structure factors obtained via exact diagonalization with those from inelastic neutron scattering experiments, we find an antiferromagnetic $\Gamma$ interaction, which dictates the Ising axis and explains the mechanism behind moment pinning. Our theory suggests that CoNb$_2$O$_6$ represents a rare one-dimensional Kitaev chain with significant ferromagnetic Kitaev and antiferromagnetic Gamma interactions.

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Derek Churchill, Hae-Young Kee. 2024-03-21. Transforming from Kitaev to Disguised Ising Chain: Application to CoNb$_2$O$_6$. https://doi.org/10.1103/physrevlett.133.056703

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