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arXiv 2005.07745cond-mat.str-el
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二维量子海森堡反铁磁体共面和共线磁序纠缠和Rényi熵的自旋波研究

Spin-wave study of entanglement and Rényi entropy for coplanar and collinear magnetic orders in two-dimensional quantum Heisenberg antiferromagnets

Dag-Vidar Bauer, J. O. Fjærestad

摘要:

本文利用改进的线性自旋波理论(MLSWT)研究了具有共面螺旋磁序的正方形和三角形格子$L\times L$量子海森堡反铁磁体中长度为$L$的线子系统的基态纠缠,其中$q=π$(共线序,$N_G=2$)除外,序矢量为$\mathbf{Q}=(q,q)$和$N_G=3$ Goldstone模.将早期的$q=π$的MLSWT结果推广到具有$s\geq 3$子晶格的公度螺旋序($q=2πr/s$与$r$和$s$互质),我们发现解析大$L$的通用和$n$独立的子领导项$(N_G/2)\ln L$雷尼熵$S_n$,与$λ_0$和$λ_{\pm q}$的$L^{1/2}$标度,与$λ_0\neq λ_{\pm q}$螺旋顺序;这里,$\{λ_{k_y}\}$是纠缠哈密顿量的$L$模式占用数。$S_n$中的术语$(3/2)\ln L$与$s=3$螺旋序($q=2π/3$)的非线性sigma模型(NLSM)研究一致。这些和其他属性的$S_n$和$λ_{k_y}$探索数值各向异性最近邻三角晶格模型,$q$在螺旋相位变化。

英文摘要:

We use modified linear spin-wave theory (MLSWT) to study ground-state entanglement for a length-$L$ line subsystem in $L\times L$ square- and triangular-lattice quantum Heisenberg antiferromagnets with coplanar spiral magnetic order with ordering vector $\mathbf{Q}=(q,q)$ and $N_G=3$ Goldstone modes, except if $q=π$ (collinear order, $N_G=2$). Generalizing earlier MLSWT results for $q=π$ to commensurate spiral order with $s\geq 3$ sublattices ($q=2πr/s$ with $r$ and $s$ coprime), we find analytically for large $L$ a universal and $n$-independent subleading term $(N_G/2)\ln L$ in the Rényi entropy $S_n$, associated with $L^{1/2}$ scaling of $λ_0$ and $λ_{\pm q}$, with $λ_0\neq λ_{\pm q}$ for spiral order; here $\{λ_{k_y}\}$ are the $L$ mode occupation numbers of the entanglement Hamiltonian. The term $(3/2)\ln L$ in $S_n$ agrees with a nonlinear sigma model (NLSM) study of $s=3$ spiral order ($q=2π/3$). These and other properties of $S_n$ and $λ_{k_y}$ are explored numerically for an anisotropic nearest-neighbor triangular-lattice model for which $q$ varies in the spiral phase.

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