Novel quantum state in a high-spin chain created by the spontaneous symmetry breaking

在这个项目中，我们探索了有限场基态的各种高自旋（主要是，S=1）链，采用数值和分析方法。主要结果如下：1.一维S=1单轴各向异性能铁磁-反铁磁键交替链我们用密度矩阵重整化群方法研究了该系统的有限场基态，并且阐明了在基态磁化曲线中出现两种1/2平台（饱和磁化强度一半处的磁化平台）。此外，利用基于有限尺寸系统精确对角化方法的能级谱方法，我们确定了相互作用参数平面上的1/2磁化平台相图和磁场-相互作用参数平面上的磁化相图. 2.各向异性一维S=1反 ...更多信息 铁磁链我们用密度矩阵重整化群方法研究了具有Ising型各向异性交换作用和单轴单离子各向异性能的一维反铁磁链的有限场基态。得到的结果是：i）在基态磁化曲线中出现了对应于一级相变的磁化跳变异常，ii）在有限场基态中发生了对应于二级相变的无公度-无公度相变。3.具有键交替最近邻和均匀次最近邻相互作用的一维S=1链首先，本文计算了铁磁态自旋波激发的色散关系，并由此严格确定了相互作用参数平面上铁磁相和单重态之间的相边界线。然后，我们用密度矩阵重整化群方法计算了非磁性单重态相稳定的参数区域内的基态磁化曲线，发现磁化曲线上出现了1/2平台。最后，我们用能级谱方法确定了相互作用参数平面上的1/2平台相图。少

In this project, we have explored the finite-field ground states of a variety of high-spin (mainly, S=1) chains, employing numerical and analytical methods. The main results which we have obtained are summarized as follows.1.One-Dimensional S=1 Ferromagnetic-Antiferromagnetic Bond-Alternating Chain with Uniaxial Single-IonAnisotropy EnergiesWe have examined the finite-field ground state of the present system by means of the density-matrix renormalization-group method, and clarified that two kinds of 1/2-plateaux (the magnetization plateau at the half of the saturation magnetization) appear in the ground-state magnetization curve. Furthermore, employing the level spectroscopy method based on the exact diagonalization method for finite-size systems, we have determined the 1/2-magnetization plateau phase diagram on the plane of the interaction parameters and also the magnetization phase diagram on the magnetic field versus interaction parameter plane.2.Anisotropic One-Dimensional S=1 Anti … More ferromagnetic ChainWe have studied, by means of the density-matrix renormalization-group method, the finite-field ground state of the one-dimensional antiferromagnetic chain with Ising-type anisotropic exchange interactions and uniaxial single-ion anisotropy energies. The obtained results are : i)The magnetization jump anomaly corresponding to the first-order phase transition appears in the ground-state magnetization curve, and ii)the commensurate-incommensurate phase transition corresponding to the second-order one takes place in the finite-field ground state.3.One-Dimensional S=1 Chain with Bond-Alternating Nearest-Neighbor and Uniform Next-Nearest-Neighbor InteractionsFirst, we have calculated the dispersion relation of the spin-wave excitation from the ferromagnetic state, from the result of which we have rigorously determined the phase boundary line between the ferromagnetic and nonmagnetic singlet phases on the plane of the interaction parameters. Then, we have calculated, using the density-matrix renormalization-group method, the ground-state magnetization curve in the parameter region where the non-magnetic singlet phase is stable, and found that the 1/2-plateau appears in the magnetization curve. Finally, we have determined the 1/2-plateau phase diagram on the plane of the interaction parameters by applying the level spectroscopy method. Less