STRING CORRELATION OF QUANTUM ANTIFERROMAGNETIC SPIN CHAINS WITH S = 1 AND 2

Antiferromagnetic Heisenberg spin chains for S = 1 and S = 2 are treated numerically. We investigate a generalized theta-string correlation function O(theta)(j) = [S1z exp (itheta SIGMA(k = 1)j-1 S(k)z)S(j)z] which is a generalization of the string correlation function of den Nijs-Rommelse. When the value of theta lies in an appropriate region, the phase of O(theta)(j) is fixed and O(theta)(j) behaves smoothly as a function of j. This means alternative sign changes of the usual spin-spin correlation O(theta = 0)(j) are well canceled in O(theta)(j) for such values of theta. The cancellation is best at theta = pi and pi/2 for the S = 1 and 2 cases, respectively. The generalized string which appears in the theta-string correlation function plays a role similar to that of a fictitious gauge potential in the definition of the hidden order parameter of the fractional quantized Hall state by Girvin and MacDonald.