CRITICAL EXPONENT ETA IN S=1 ANTIFERROMAGNETIC HEISENBERG-CHAINS WITH ALTERNATING INTERACTION

Low-temperature properties of S= 1 antiferromagnetic Heisenberg chains with alternating interaction, H=J Sigma(i)[1-(-1)(i) delta]S-i . S-i+1, are studied by a quantum Monte Carlo method. Spatial distributions of the spin correlation function [(S1Siz)-S-z] and the local magnetic moment [S-i(z)] are visualized as a function of delta. The continuous phase transition at delta=0.25, which was indicated by several authors, is confirmed by the S dependence of the low-lying level structure, the divergence of the correlation length, and also the collapse of the edge states. The critical exponent eta, 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-g ones may be described in terms of the generic critical theory.