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arXiv 1708.03232cond-mat.str-el
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正方晶格自旋为1/2的海森堡反铁磁体中自旋子的近退禁闭激发

Nearly deconfined spinon excitations in the square-lattice spin-1/2 Heisenberg antiferromagnet

Hui Shao, Yan Qi Qin, Sylvain Capponi, Stefano Chesi, Zi Yang Meng, Anders W. Sandvik

摘要:

本文研究了自旋- $1/2$正方晶格海森堡反铁磁体和$J$ - $Q$模型(含4自旋相互作用$Q$和海森堡交换$J$)的动态自旋结构因子.用改进的方法对QMC模拟计算的时空关联函数进行随机解析延拓,可以处理自旋波(磁振子)和高能连续谱的尖锐贡献($δ$ -函数)。Heisenberg模型的结果与Cu(DCOO)$_2$ $\cdot$ 4D $_2$ O的中子散射实验一致,其中在$q=(π,0)$处的宽谱重连续谱被解释为退禁闭自旋。我们在$(π,0)$的结果显示了类似的磁振子重量的减少和一个大的连续谱,而在$q=(π/2,π/2)$的连续谱要小得多(也可以从实验中看到)。打开$Q$,我们观察到$(π,0)$磁振子的重量迅速减少到零,在解除量子相变到一个自发的二聚状态。我们重新解释了在$(π,0)$实验中的退禁闭自旋子的图像为近退禁闭自旋子-退禁闭量子临界性的先驱。为了进一步阐明海森堡模型中一个脆弱的$(π,0)$ -磁振子以及它在$J$ - $Q$模型中的耗尽,我们引入了一个有效的模型,在这个模型中,一个磁振子可以分裂成两个自旋子,这两个自旋子不分离,而是在磁振子空间内外波动(类似于激子-极化激元问题中光子和粒子-空穴对之间的共振)。该模型再现了海森堡模型的$(π,0)$和$(π/2,π/2)$特征。它也可以解释随着$Q$的增加,$(π,0)$磁振子的快速损失,以及即使在去精细临界点,在$q=(π/2,π/2)$仍有一个大的磁振子极。

英文摘要:

We study the dynamic spin structure factor of the spin-$1/2$ square-lattice Heisenberg antiferromagnet and of the $J$-$Q$ model (with 4-spin interactions $Q$ and Heisenberg exchange $J$). Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with QMC simulations, we can treat the sharp ($δ$-function) contribution from spinwaves (magnons) and a continuum at higher energy. The results for the Heisenberg model agree with neutron scattering experiments on Cu(DCOO)$_2$$\cdot$4D$_2$O, where a broad spectral-weight continuum at $q=(π,0)$ was interpreted as deconfined spinons. Our results at $(π,0)$ show a similar reduction of the magnon weight and a large continuum, while the continuum is much smaller at $q=(π/2,π/2)$ (as also seen experimentally). Turning on $Q$, we observe a rapid reduction of the $(π,0)$ magnon weight to zero, well before the deconfined quantum phase transition into a spontaneously dimerized state. We re-interpret the picture of deconfined spinons at $(π,0)$ in the experiments as nearly deconfined spinons---a precursor to deconfined quantum criticality. To further elucidate the picture of a fragile $(π,0)$-magnon in the Heisenberg model and its depletion in the $J$-$Q$ model, we introduce an effective model in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy with the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model reproduces the $(π,0)$ and $(π/2,π/2)$ features of the Heisenberg model. It can also account for the rapid loss of the $(π,0)$ magnon with increasing $Q$ and a remarkable persistence of a large magnon pole at $q=(π/2,π/2)$ even at the deconfined critical point.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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