Phase Transitions of S = 3/2 and S = 2 XXZ Spin Chains with Bond Alternation

Based on the universality. concept, we study the S = 3/2 and S = 2 bond-alternating spin chains numerically. In previous papers, the phase diagram of the S = 1 XXZ spin chain with bond alternation was shown to reflect the hidden Z₂ × Z₂ symmetry. For the higher S Heisenberg spin chain, the successive dimerization transition occurs, and for anisotropic spin chains the phase structure will be more colorful than the S = 1 case. Using recently developed techniques, we show directly that the phase structure of the anisotropic spin chains relates to the Z₂ × Z₂ symmetry.