强各向异性三角XXZ模型的磁激发：一种投影自旋乘积态方法
Magnetic excitations of the strongly-anisotropic triangular XXZ model: a projected spin-product state approach
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中文总结 AI 辅助
本文提出一种投影自旋乘积态近似方法，用于研究强各向异性三角XXZ模型的磁激发，该方法在描述KCSO材料的激发谱时优于线性自旋波理论，但赝Goldstone间隙和低场色散仍有偏差。
中文摘要 AI 辅助
最近的实验激发了人们对具有强Ising类各向异性的自旋-1/2三角XXZ模型的基态性质和激发谱的兴趣。在本工作中，我们引入并分析了一种该模型的“投影”相干态近似，该近似通过将自旋乘积态投影到三角Ising反铁磁体的低能构型上而构建。在此近似下，我们讨论了基态有序结构以及纵向场下的磁化曲线。随后，我们通过线性化由含时变分原理导出的运动方程来讨论激发谱。这导致了在强约束希尔伯特空间内对类自旋波激发的自然描述。在零场下，变分近似导致准简并态的非常平坦的景观，这导致激发谱中出现低能赝Goldstone模。我们将我们的结果与钴氧化物K$_{2}$Co(SeO$_{3}$)$_{2}$（KCSO）的实验测量进行比较。与线性自旋波理论相比，我们的近似带来了显著的改进。然而，在低场下，赝Goldstone间隙的值以及M点附近的色散仍存在偏差。
英文摘要
Recent experiments have sparked interest on the ground-state properties and on the excitation spectrum of the spin-$1/2$ triangular XXZ model with strong Ising-like anisotropy. In this work, we introduce and analyze a ``projected'' coherent-state approximation to the model, constructed by projecting spin-product states onto the low-energy configurations of the triangular Ising antiferromagnet. Within this approximation, we discuss the structure of the ground-state ordering and the magnetization curve under a longitudinal field. We then discuss the excitation spectrum by linearizing equations of motion deriving from a time-dependent variational principle. This leads to a natural description of spin-wave-like excitations within the strongly constrained Hilbert space. At zero field, the variational approximation leads to a very flat landscape of quasi-degenerate states, which results in a low-energy pseudo-Goldstone mode in the excitation spectrum. We compare our results to experimental measurements on the cobaltite K$_{2}$Co(SeO$_{3}$)$_{2}$ (KCSO). Our approximation leads to a dramatic improvement as compared to linear spin-wave theory. However, there remain deviations in the value of the pseudo-Goldstone gap and in the dispersion near $M$ points at low field.
发表机构
- Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院物理研究所）
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