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

Abstract

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 spinchains 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.