TEMPERATURE-DEPENDENCE OF SPIN CORRELATION LENGTH OF HALF-FILLED ONE-DIMENSIONAL HUBBARD-MODEL

We have calculated the spin correlation length of the half-filled one-dimensional Hubbard model down to the temperature of T = 0.01 x (transfer integral) by the Bethe-Ansatz method for the quantum transfer matrix. Its temperature dependence shows the crossover from (2 log pi-T)-1 at high temperatures to aT-1 with the log corrections at low temperatures, the low-T behavior being consistent with the prediction by the conformal field theory. When the Coulomb repulsion U is small, we have found at low temperatures another crossover in the proportional constant a from the value for the free electron system to that for the antiferromagnetic Heisenberg model. This crossover is due to the disappearance of charge fluctuation. A similar crossover has been observed for the linear coefficient of specific heat, C/T.