Li Xuanyi, Xu Changsong, Liu Boyu, Li Xueyang, Bellaiche L, Xiang Hongjun
Key Laboratory of Computational Physical Sciences (Ministry of Education), Institute of Computational Physical Sciences, State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, China.
Shanghai Qi Zhi Institute, Shanghai 200030, China.
Phys Rev Lett. 2023 Jul 21;131(3):036701. doi: 10.1103/PhysRevLett.131.036701.
A realistic first-principle-based spin Hamiltonian is constructed for the type-II multiferroic NiI_{2}, using a symmetry-adapted cluster expansion method. Besides single ion anisotropy and isotropic Heisenberg terms, this model further includes the Kitaev interaction and a biquadratic term, and can well reproduce striking features of the experimental helical ground state, that are, e.g., a proper screw state, canting of rotation plane, propagation direction, and period. Using this model to build a phase diagram, it is demonstrated that, (i) the in-plane propagation direction of ⟨11[over ¯]0⟩ is determined by the Kitaev interaction, instead of the long-believed exchange frustrations and (ii) the canting of rotation plane is also dominantly determined by Kitaev interaction, rather than interlayer couplings. Furthermore, additional Monte Carlo simulations reveal three equivalent domains and different topological defects. Since the ferroelectricity is induced by spins in type-II multiferroics, our work also implies that Kitaev interaction is closely related to the multiferroicity of NiI_{2}.
利用对称适配团簇展开方法，为II型多铁性材料NiI₂构建了一个基于第一性原理的现实自旋哈密顿量。除了单离子各向异性和各向同性海森堡项外，该模型还进一步包括了基泰耶夫相互作用和双二次项，并且能够很好地再现实验螺旋基态的显著特征，例如合适的螺旋态、旋转平面的倾斜、传播方向和周期。使用该模型构建相图表明，（i）〈11[上划线]0〉的面内传播方向由基泰耶夫相互作用决定，而不是长期以来认为的交换失稳；（ii）旋转平面的倾斜也主要由基泰耶夫相互作用决定，而不是层间耦合。此外，额外的蒙特卡罗模拟揭示了三个等效畴和不同的拓扑缺陷。由于II型多铁性材料中的铁电性是由自旋诱导的，我们的工作还意味着基泰耶夫相互作用与NiI₂的多铁性密切相关。
