Exact diagonalization and cluster mean-field study of triangular-lattice XXZ antiferromagnets near saturation
Exact diagonalization and cluster mean-field study of triangular-lattice XXZ antiferromagnets near saturation
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DOI：
10.1103/physrevb.96.014431
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发表时间：
2017-04
影响因子：
3.7
通讯作者：
D. Yamamoto;H. Ueda;I. Danshita;G. Marmorini;T. Momoi;T. Shimokawa
中科院分区：
文献类型：
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作者：
D. Yamamoto;H. Ueda;I. Danshita;G. Marmorini;T. Momoi;T. Shimokawa
具有XXZ各向异性的三角晶格反铁磁体的磁饱和附近的量子磁相引起了人们的新的兴趣，因为有人提出，除了已知的0-共面（也称为$V$）和伞形相之外，在一定的各向异性参数$J/J_z$范围内，还可以通过量子效应稳定一个非平凡的共面相，称为$\pi$-共面或$\Psi$相。最近，Sellmann $et$al$。[Phys. Rev. B {\bf 91}，081104（R）（2015）]声称在希尔伯特空间中只有三个下自旋（三个磁振子）的扇区中，从精确对角化分析中，对于$S=1/2$，不存在$\pi$-共面相位。我们首先重新考虑并改进了这一分析，考虑到几个低的本征值和相关的本征态作为一个函数的$J/J_z$，并通过合理地增加系统的大小（高达1296自旋）。仔细的识别分析表明，最低本征态是一个手征反对称的有限大小的伞态的组合$J/J_z\gtrsim 2.218$，而它对应于一个共面相位$J/J_z\lesssim 2.218$。然而，我们证明，0-共面和$\pi$-共面相位之间的区别在后一个区域是根本不可能的，从保序有限尺寸计算与固定的磁振子数。因此，我们也进行了集群平均场加标度分析小自旋$S\leq 3/2$。结果表明，除了经典极限（$S\rightarrow \infty$）外，对于任意的$S$，都存在$\pi$-共面相位，并且在最量子化的情况下，$S=1/2$，$J/J_z$中的存在范围最大.
Quantum magnetic phases near the magnetic saturation of triangular-lattice antiferromagnets with XXZ anisotropy have been attracting renewed interest since it has been suggested that a nontrivial coplanar phase, called the $\pi$-coplanar or $\Psi$ phase, could be stabilized by quantum effects in a certain range of anisotropy parameter $J/J_z$ besides the well-known 0-coplanar (known also as $V$) and umbrella phases. Recently, Sellmann $et$ $al$. [Phys. Rev. B {\bf 91}, 081104(R) (2015)] claimed that the $\pi$-coplanar phase is absent for $S=1/2$ from an exact-diagonalization analysis in the sector of the Hilbert space with only three down-spins (three magnons). We first reconsider and improve this analysis by taking into account several low-lying eigenvalues and the associated eigenstates as a function of $J/J_z$ and by sensibly increasing the system sizes (up to 1296 spins). A careful identification analysis shows that the lowest eigenstate is a chirally antisymmetric combination of finite-size umbrella states for $J/J_z\gtrsim 2.218$ while it corresponds to a coplanar phase for $J/J_z\lesssim 2.218$. However, we demonstrate that the distinction between 0-coplanar and $\pi$-coplanar phases in the latter region is fundamentally impossible from the symmetry-preserving finite-size calculations with fixed magnon number.} Therefore, we also perform a cluster mean-field plus scaling analysis for small spins $S\leq 3/2$. The obtained results, together with the previous large-$S$ analysis, indicate that the $\pi$-coplanar phase exists for any $S$ except for the classical limit ($S\rightarrow \infty$) and the existence range in $J/J_z$ is largest in the most quantum case of $S=1/2$.