Random-Singlet Phase in Disordered Two-Dimensional Quantum Magnets
Random-Singlet Phase in Disordered Two-Dimensional Quantum Magnets
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无序二维量子磁体中的随机单线相
DOI：
10.1103/physrevx.8.041040
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发表时间：
2018
影响因子：
12.5
通讯作者：
vik
中科院分区：
文献类型：
--
作者：
Lu Liu;Hui Shao;Yu-Cheng Lin;Wenan Guo;Anders W. S;vik
本文研究了二维正方格子S=1/2量子自旋系统中的无序效应，即具有6自旋相互作用Q补充海森堡交换J的J-Q模型.在没有无序的情况下，系统主机反铁磁（AFM）和柱状价键固体（VBS）基态。VBS破坏了Z_4对称性，并且在任意弱无序的情况下，它形成畴。使用QMC模拟，我们证明了两种这样的无序VBS状态。在稀释时，被移除的位置在相对的子晶格中留下局部自旋。这些自旋形成AFM有序。对于随机相互作用，我们发现一个不同的状态，没有秩序，但代数衰减的平均相关性。我们确定本地化的自旋在不同的VBS模式之间的域壁的连接。这些自旋子形成具有相同数目的自旋子和反自旋子的相关群。在这样的一组中，有一个强烈的倾向，单态形成，因为自旋-自旋相互作用介导的域壁。因此，没有长程AFM有序形式。我们建议，这种状态是一个2D模拟的著名的1D随机单态（RS）的状态，虽然在2D的动态指数$z$是有限的。通过对T相关磁化率的研究，我们发现在AFM-RS相界z=2，在RS相中z=2，在无几何阻挫系统中发现的RS态应该与最近提出的阻挫系统的RS态对应同一个不动点，并且在没有蒙特卡罗符号问题的情况下研究它的能力为进一步详细表征其静态和动态特性提供了机会。我们还讨论了准二维正方晶格随机交换量子磁体Sr 2 CuTe 1-x W xO 6中RS相的实验证据。
We study effects of disorder (randomness) in a 2D square-lattice $S=1/2$ quantum spin system, the $J$-$Q$ model with a 6-spin interaction $Q$ supplementing the Heisenberg exchange $J$. In the absence of disorder the system hosts antiferromagnetic (AFM) and columnar valence-bond-solid (VBS) ground states. The VBS breaks $Z_4$ symmetry, and in the presence of arbitrarily weak disorder it forms domains. Using QMC simulations, we demonstrate two kinds of such disordered VBS states. Upon dilution, a removed site leaves a localized spin in the opposite sublattice. These spins form AFM order. For random interactions, we find a different state, with no order but algebraically decaying mean correlations. We identify localized spinons at the nexus of domain walls between different VBS patterns. These spinons form correlated groups with the same number of spinons and antispinons. Within such a group, there is a strong tendency to singlet formation, because of spinon-spinon interactions mediated by the domain walls. Thus, no long-range AFM order forms. We propose that this state is a 2D analog of the well-known 1D random singlet (RS) state, though the dynamic exponent $z$ in 2D is finite. By studying the T-dependent magnetic susceptibility, we find that $z$ varies, from $z=2$ at the AFM--RS phase boundary and larger in the RS phase The RS state discovered here in a system without geometric frustration should correspond to the same fixed point as the RS state recently proposed for frustrated systems, and the ability to study it without Monte Carlo sign problems opens up opportunities for further detailed characterization of its static and dynamic properties. We also discuss experimental evidence of the RS phase in the quasi-two-dimensional square-lattice random-exchange quantum magnets Sr$_2$CuTe$_{1-x}$W$_x$O$_6$.