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arXiv 1406.3686cond-mat.str-el
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一维非线性链的解析和数值研究

Analytical and numerical studies of the one-dimensional sawtooth chain

Jian-Jun Jiang, Yong-Jun Liu, Fei Tang, Cui-Hong Yang, Yu-Bo Sheng

摘要:

利用解析耦合集团方法、数值精确对角化方法和数值密度矩阵重整化群方法,研究了一维非线性链的性质.基于Neel态的耦合团簇方法计算结果表明,当a<ac 1时,基态处于准Neel-长程序态。基态的平移对称性发生变化,基态从准Neel-长程序态演化到临界点ac 1处的二聚态。二聚化态在中间参数区是稳定的,在另一个临界点ac 2处消失。精确对角化的结果表明,分别用自旋刚度、保真度、磁化率和自旋能隙可以精确地确定临界点ac 1和ac 2。比较了基于倾斜态的耦合团簇方法和基于螺旋态的耦合团簇方法的计算结果,发现当a> ac 2时,链的基态为准倾斜态.耦合团簇方法和密度矩阵重整化群方法的结果都揭示了在ac 2处发生的量子相变类型属于一级相变。

英文摘要:

By using the analytical coupled cluster method, the numerical exact diagonalization method, and the numerical density matrix renormalization group method, we investigated the properties of the one-dimensional sawtooth chain. The results of the coupled cluster method based on Neel state demonstrate that the ground state is in the quasi-Neel-long-range order state when a<ac1. The translational symmetry of the ground state varies and the ground state evolves from the quasi-Neel-long-range order state to the dimerized state at the critical point ac1. The dimerized state is stable in the intermediate parameter regime and vanishes at another critical point ac2. The results drawn from the exact diagonalization show that the precise critical point ac1 and ac2 can be determined by using the spin stiffness fidelity susceptibility and spin gap separately. We compared the results obtained by using the coupled cluster method based on canted state with those obtained based on spiral state, and found that the ground state of the sawtooth chain is in the quasi-canted state if a>ac2. The results of the coupled cluster method and the density matrix renormalization group method both disclose that the type of the quantum phase transition occurring at ac2 belongs to the first-order transition.

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