STRING CORRELATION-FUNCTIONS IN THE ANISOTROPIC SPIN-1 HEISENBERG CHAIN

We study the string correlation functions proposed by den Nijs and Rommelse for the S = 1 XXZ Hamiltonian by an exact diagonalization method. Using a finite size analysis, we estimate values of the string order parameters in the thermodynamic limit. Using the extrapolated values of the string order parameter we investigate the phase boundary between the two expected phases of the model, namely, the massive Haldane phase and the x-y-like massless phase. In the massless phase the exponent of the string correlation functions on the periodic system seems to be given by dimensions, which normally occur in the operator content of the chain when antiperiodic boundary condition is imposed.