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首页> 外文期刊>Physical Review X >Nearly Deconfined Spinon Excitations in the Square-Lattice Spin- 1 / 2 Heisenberg Antiferromagnet
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Nearly Deconfined Spinon Excitations in the Square-Lattice Spin- 1 / 2 Heisenberg Antiferromagnet

机译：在方形格子旋转 - 1/2 Heisenberg反杀菌中几乎欺骗了菠菜激发

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We study the spin-excitation spectrum (dynamic structure factor) of the spin- 1 / 2 square-lattice Heisenberg antiferromagnet and an extended model (the J ? Q model) including four-spin interactions Q in addition to the Heisenberg exchange J . Using an improved method for stochastic analytic continuation of imaginary-time correlation functions computed with quantum Monte?Carlo simulations, we can treat the sharp ( δ -function) contribution to the structure factor expected from spin-wave (magnon) excitations, in addition to resolving a continuum above the magnon energy. Spectra for the Heisenberg model are in excellent agreement with recent neutron-scattering experiments on Cu ( DCOO ) 2 · 4 D 2 O , where a broad spectral-weight continuum at wave vector q = ( π , 0 ) was interpreted as deconfined spinons, i.e., fractional excitations carrying half of the spin of a magnon. 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). We further investigate the reasons for the small magnon weight at ( π , 0 ) and the nature of the corresponding excitation by studying the evolution of the spectral functions in the J ? Q model. Upon turning on the Q interaction, we observe a rapid reduction of the magnon weight to zero, well before the system undergoes a deconfined quantum phase transition into a nonmagnetic spontaneously dimerized state. Based on these results, we reinterpret 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 pole in the Heisenberg model and its depletion in the J ? Q model, we introduce an effective model of the excitations in which a magnon can split into two spinons that do not separate but fluctuate in and out of the magnon space (in analogy to the resonance between a photon and a particle-hole pair in the exciton-polariton problem). The model can reproduce the reduction of magnon weight and lowered excitation energy at ( π , 0 ) in the Heisenberg model, as well as the energy maximum and smaller continuum at ( π / 2 , π / 2 ) . It can also account for the rapid loss of the ( π , 0 ) magnon with increasing Q and the remarkable persistence of a large magnon pole at q = ( π / 2 , π / 2 ) even at the deconfined critical point. The fragility of the magnons close to ( π , 0 ) in the Heisenberg model suggests that various interactions that likely are important in many materials—e.g., longer-range pair exchange, ring exchange, and spin-phonon interactions—may also destroy these magnons and lead to even stronger spinon signatures than in Cu ( DCOO ) 2 · 4 D 2 O .
机译：除了Heisenberg Exchange J之外，我们研究了Spin-1/2平方英格Heisenberg反霉菌和扩展模型（J-Q模型）的扩展模型（J-Q模型）的旋转激励谱（动态结构因子）。利用随机分析的改进方法使用量子蒙特·莫斯特（Moneum Monte）模拟的假想时间相关功能，我们可以将夏普（Δfunction）对预期的结构因子进行贡献，除了解决高于Magnon能量的连续体。 Heisenberg模型的光谱与Cu（DCOO）2·4d 2 O的最近中子散射实验非常一致，其中波载体Q =（π,0）的宽光谱重量连续核被解释为脱诺纺硅，即，携带一半的旋转肿块的分数激动。我们的结果在（π,0）上显示了类似的肉质重量和大连续体的减少，而连续体在Q =（π/ 2，π/ 2）下更小（如实验）。我们进一步研究了在（π，0）的小氧元重量的原因，并通过研究J的谱函数的演变来研究相应的激励的性质？ q模型。在接通Q相互作用时，我们观察氧元重至零的快速降低，良好地在系统经历解核量子相转变为非磁性自发二聚体状态之前。基于这些结果，我们在实验中重新诠释了在（π，0）中的Deconfined Spinons的图片，作为几乎欺骗的旋转纺丝 - 一种去核化量子临界性的前体。为了进一步阐明Heisenberg模型中脆弱（π，0）-magnon杆的图像及其在J中的耗尽？ Q模型，我们介绍了一个有效的激励模型，其中隆隆可以分成一个不分开但在氧元空间中（类似于光子和粒子孔对中的共振而流出的两个旋转旋转激子 - Polariton问题）。该模型可以在Heisenberg模型中再现Magnon重量和降低的激发能量，并且在（π/ 2，π/ 2）中的能量最大值和更小的连续轴。它还可以考虑（π，0）氧化的快速损失，即使在Q =（π/ 2，π/ 2）中也是Q =（π/ 2，π/ 2）的显着持久性，即使在折垃圾临界点也是如此。 Heisenberg模型中靠近（π，0）的齿轮箱的脆弱性表明，许多材料中可能是重要的各种相互作用 - 例如，更长的对交换，环形交换和旋转声子相互作用 - 也可能摧毁这些千块子并且导致旋转型甚至比在Cu（DCOO）2·4 d 2 O中更强。

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