MAGNETIC SHORT-RANGE ORDER VERSUS LONG-RANGE ORDER IN THE HUBBARD-MODEL

A theory of magnetic short-range order in the paraphase of the one-band Hubbard model is presented on the basis of the four-field slave-boson approach. In the functional-integral scheme the bosonized action, expressed in terms of fluctuating local magnetizations and internal magnetic fields, is transformed to an effective Ising model treated in the Bethe-cluster approximation. The theory is evaluated in the saddle-point approximation including short-range-order effects in a fully self-consistent way. Comparing our results with previous approaches, the ground-state phase diagram shows the suppression of antiferromagnetic and incommensurate spiral long-range-ordered phases in the favor of a paraphase with short-range order in a wide doping region. Using realistic values of the on-site Coulomb repulsion for La2-xSrxCuO4, U/t similar or equal to 8, the critical doping concentration for the destruction of antiferromagnetism is obtained as 3-4%, in agreement with experiments.