STRING CORRELATIONS OF THE ANTIFERROMAGNETIC SPIN-1 CHAIN - EXCITED-STATES AND MAGNETIC-FIELD EFFECTS

We calculate energies and wave functions of S = 1 antiferromagnetic Heisenberg chains with single-ion anisotropy in a symmetry-breaking external magnetic field. From results for the string correlation function for low-lying excited states we identify these states as solitons with respect to the hidden string order. For finite anisotropic chains we investigate the transition to the fully magnetized state at high magnetic fields and conclude that Bose condensation in an external magnetic field occurs also for the anisotropic chain.