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arXiv 1702.05950cond-mat.str-elcond-mat.stat-mech
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具有无限投影纠缠对态的量子临界相

Quantum critical phase with infinite projected entangled paired states

Didier Poilblanc, Matthieu Mambrini

摘要:

Mambrini等人最近提出了一种基于唯一的格点张量的SU(2)不变投影纠缠对态(PEPS)的分类方法。\cite{Mambrini2016}。目前还不清楚这种SU(2)不变的PEPS是否可以i)表现出长程磁序(如Néel相),或者ii)描述一个真正的量子临界点(QCP)或量子临界相(QCPh),将两个有序相分开。在这里,我们确定了一个特定的SU(2)不变PEPS的分类,它提供了良好的变分能量的$J_1-J_2$挫折海森堡模型,特别是在$J_2=0.5$,对应的QCP或QCPh的近似位置分离的Néel相位从二聚相位。PEPS由属于$\frac{1}{2}^{\otimes N} \oplus 0$ SU(2)表示的虚拟状态构建,即具有虚拟\hbox{spin-$\frac{1}{2}$}的$N$“颜色”。在热力学极限下,基于角转移矩阵重正化算法和共轭梯度优化方法,采用完全更新的无限PEPS方法,我们证明了i)磁序的不存在和ii)发散的关联长度(即,随着环境维度的增加,没有显示饱和的迹象)。我们认为,这样的PEPS给出了定性描述的QCP或QCPh的$J_1-J_2$模型。

英文摘要:

A classification of SU(2)-invariant Projected Entangled Paired States (PEPS) on the square lattice, based on a unique site tensor, has been recently introduced by Mambrini et al.~\cite{Mambrini2016}. It is not clear whether such SU(2)-invariant PEPS can either i) exhibit long-range magnetic order (like in the Néel phase) or ii) describe a genuine quantum critical point (QCP) or quantum critical phase (QCPh) separating two ordered phases. Here, we identify a specific family of SU(2)-invariant PEPS of the classification which provides excellent variational energies for the $J_1-J_2$ frustrated Heisenberg model, especially at $J_2=0.5$, corresponding to the approximate location of the QCP or QCPh separating the Néel phase from a dimerized phase. The PEPS are build from virtual states belonging to the $\frac{1}{2}^{\otimes N} \oplus 0$ SU(2)-representation, i.e. with $N$ "colors" of virtual \hbox{spin-$\frac{1}{2}$}. Using a full update infinite-PEPS approach directly in the thermodynamic limit, based on the Corner Transfer Matrix renormalization algorithm supplemented by a Conjugate Gradient optimization scheme, we provide evidence of i) the absence of magnetic order and of ii) diverging correlation lengths (i.e. showing no sign of saturation with increasing environment dimension) in both the singlet and triplet channels, when the number of colors $N\ge 3$. We argue that such a PEPS gives a qualitative description of the QCP or QCPh of the $J_1-J_2$ model.

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