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arXiv 1009.0691cond-mat.str-el
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二维中一阶Néel到价键固体跃迁的例子

Example of a first-order Néel to Valence-Bond-Solid transition in two-dimensions

Arnab Sen, Anders W. Sandvik

摘要:

本文考虑正方晶格上具有最近邻相互作用$J$和多自旋相互作用$Q_3$的$S=1/2$海森堡模型. $Q_3$项由三个键单重投影组成,选择它有利于形成价键固体(VBS),其中价键(单重对)形成交错模式。该模型表现出从Néel态到VBS的量子相变作为$Q_3/J$的函数。我们使用量子蒙特卡罗(随机级数展开)模拟研究模型。在这种情况下,Néel-VBS转变在本质上是强烈的一阶,与之前研究的类似模型相比,连续转变为柱状VBS状态。定性上不同的跃迁说明了在后一种情况下出现的U(1)对称性的重要作用,这在本模型中是不可能的,因为交错的VBS模式(不允许旋转局部VBS序参量所需的局部波动)。

英文摘要:

We consider the $S=1/2$ Heisenberg model with nearest-neighbor interaction $J$ and an additional multi-spin interaction $Q_3$ on the square lattice. The $Q_3$ term consists of three bond-singlet projectors and is chosen to favor the formation of a valence-bond solid (VBS) where the valence bonds (singlet pairs) form a staggered pattern. The model exhibits a quantum phase transition from the Néel state to the VBS as a function of $Q_3/J$. We study the model using quantum Monte Carlo (stochastic series expansion) simulations. The Néel-VBS transition in this case is strongly first-order in nature, in contrast to similar previously studied models with continuous transitions into columnar VBS states. The qualitatively different transitions illustrate the important role of an emerging U(1) symmetry in the latter case, which is not possible in the present model due to the staggered VBS pattern (which does not allow local fluctuations necessary to rotate the local VBS order parameter).

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