Critical exponent η inS=1 antiferromagnetic Heisenberg chains with alternating interaction

Low-temperature properties of S=1 antiferromagnetic Heisenberg chains with alternating interaction, scrH=${\mathit{Jtsum}}_{\mathit{i}}$[1-(-1${)}^{\mathit{i}}$δ]${\mathrm{S}}_{\mathit{i}}$⋅${\mathrm{S}}_{\mathit{i}+1\mathrm{}}$, are studied by a quantum Monte Carlo method. Spatial distributions of the spin correlation function 〈${\mathit{S}}_1^{\mathit{z}}$ ${\mathit{S}}_{\mathit{i}}^{\mathit{z}}$〉 and the local magnetic moment 〈${\mathit{S}}_{\mathit{i}}^{\mathit{z}}$〉 are visualized as a function of δ. The continuous phase transition at δ=0.25, which was indicated by several authors, is confirmed by the δ dependence of the low-lying level structure, the divergence of the correlation length, and also the collapse of the edge states. The critical exponent η, governing the power-law decay of the spin correlation function, is estimated to be 0.99±0.05. The present result raises a possibility that the variety of quantum spin chains including not only the half-odd-integer-S ones but also the integer-S ones may be described in terms of the generic critical theory.