含阻挫的不对称铁磁梯子自旋模型的量子相图

Quantum phase diagram of a frustrated asymmetric ferromagnetic spin ladder

采用严格对角化和密度矩阵重整化群方法研究阻挫和对称性对铁磁梯子基态的影响,得到体系在不对称强度参数-阻挫强度参数空间的基态相图.结果表明:在不对称性较强的体系中,随着阻挫强度的增大,系统基态从铁磁相转变为总自旋S≠0的倾斜相、再到总自旋S=0的反铁磁相;随着不对称强度参数αa的增大,倾斜相存在的阻挫强度参数区间越来越窄;当αa>0.08时,则不经历倾斜相,直接从铁磁相一阶相变为总自旋S=0的反铁磁相.

By using exact diagonalization method and density matrix renormalization group method, this paper studies the ground states of the two-leg spin-l/2 asymmetric ferromagnetic ladder model, of which the nearest-neighbor interaction is ferromagnetic （FM） and the diagonal next-nearest- neighbor interaction is antiferromagnetic （AF）. The author gives the phase diagrams of frustration versus the asymmetric strength. When the ladder is strongly asymmetric, there is a finite interme- diate frustration region occupied by the canted state phase between FM and AF phases. The phase boundaries are dependent on the asymmetric strength. On the other hand, when the asymmetric strength is not strong enough, the ground state demonstrates a first order phase transition from fer- romagnetism to antiferromagnetism as frustration increasing.