发表机构
Tohoku University（东北大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出 Schwinger 玻色子微扰框架研究自旋-$S$ Kitaev-Heisenberg 模型，利用 Klein 对偶性分解哈密顿量，确定相边界并计算自旋动力学，发现高自旋时自旋液体区域迅速缩小，且动力学谱保留双自旋子连续谱。
AI 中文摘要
我们为自旋-$S$ Kitaev-Heisenberg 模型发展了一套 Schwinger 玻色子微扰框架。纯 Kitaev 模型的自旋液体鞍点被用作未微扰态，并围绕该鞍点评估磁不稳定性和动力学自旋关联。我们利用 Kitaev-Heisenberg 模型固有的 Klein 对偶性，将哈密顿量精确分解为两部分。我们进行随机相位近似，取对偶变换下不变的部分作为未微扰项，并将其余在对偶变换下改变符号的部分视为微扰。我们确定了将量子自旋液体区域与相邻磁有序相分开的相边界，针对 $S=1/2$、$1$、$3/2$ 和 $2$。自旋液体区域随着 $S$ 的增加而迅速缩小，并在 $S=2$ 时变得非常狭窄。我们还计算了自旋-$S$ Kitaev-Heisenberg 模型的自旋动力学，重点关注 $S=1$，并发现修饰后的动力学自旋结构因子在有限能量下保留了宽的双自旋子连续谱，而低能谱权重在相邻磁相的序波矢处软化。因此，我们的框架能够实现磁不稳定性附近自旋动力学的热力学极限计算。
英文摘要
We develop a Schwinger boson perturbative framework for the spin-$S$ Kitaev-Heisenberg model. The spin-liquid saddle point of the pure Kitaev model is used as the unperturbed state, and magnetic instabilities and dynamical spin correlations are evaluated around this saddle point. We decompose the Hamiltonian exactly into two parts by exploiting the Klein duality intrinsic to the Kitaev-Heisenberg model. We perform the random-phase approximation by taking the part invariant under the duality transformation as the unperturbed term and treating the remaining term, which changes sign under it, as the perturbation. We determine the phase boundaries separating the quantum spin-liquid regimes from the adjacent magnetically ordered phases for $S=1/2$, $1$, $3/2$, and $2$. The spin-liquid regions shrink rapidly with increasing $S$ and become very narrow at $S=2$. We also compute the spin dynamics of the spin-$S$ Kitaev-Heisenberg model, focusing on $S=1$, and find that the dressed dynamical spin structure factor retains a broad two-spinon continuum at finite energies, while the low-energy spectral weight softens at the ordering wave vectors of the adjacent magnetic phases. Our framework thus enables thermodynamic-limit calculations of spin dynamics near magnetic instabilities.
Comments16 pages, 6 figures
