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Phase diagrams of period-4 spin chains consisting of three kinds of spins

Ken'ichi Takano
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Abstract

We study a period-4 antiferromagnetic mixed quantum spin chain consisting of three kinds of spins. When the ground state is singlet, the spin magnitudes in a unit cell are arrayed as (s-t, s, s+t, s) with integer or half-odd integer s and t (0 <= t < s). The spin Hamiltonian is mapped onto a nonlinear sigma model (NLSM) in a previously developed method. The resultant NLSM includes only two independent parameters originating from four exchange constants for fixed s and t. The topological angle in the NLSM determines the gapless phase boundaries between disordered phases in the parameter space. The phase diagrams for various s and t shows rich structures. We systematically explain the phases in the singlet-cluster-solid picture.

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Ken'ichi Takano. 2000-10-19. Phase diagrams of period-4 spin chains consisting of three kinds of spins. https://arxiv.org/abs/cond-mat/0010273

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