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Phase Diagram of the 1/2-1/2-1-1 Spin Chain by the Nonlinear Sigma Model

Ken'ichi Takano
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Abstract

We examine a periodic mixed spin chain with spin magnitudes 1/2 and 1 which are arrayed as 1/2-1/2-1-1. The three independent parameters are ratios of the four exchange couplings. We determine phase boundaries in the parameter space by using the gapless condition which was previously derived by mapping a general inhomogeneous spin chain to the nonlinear sigma model. We find two gapless boundaries separating three disordered phases. The features of the phases are explained in terms of singlet clusters.

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Ken'ichi Takano. 1999-09-30. Phase Diagram of the 1/2-1/2-1-1 Spin Chain by the Nonlinear Sigma Model. https://doi.org/10.1016/s0921-4526(99)02801-x

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