ON ANTIFERROMAGNETIC INSTABILITY IN THE HUBBARD MODEL

Abstract

A functional integral method applied to the Hubbard model has been used to construct the magnetic phase diagram (temperature versus doping) for large U/t. The antiferromagnetic order parameter has been represented in terms of fermion operators which correspond to neutral, spin one-half quasi-particles i.e. spinons. Static approximation has been applied. Numerical calculations have been performed for the two-dimensional square lattice. A stable antiferromagnetic phase for the half-filled band has been found below the critical temperature TN=J where J=4t2/U is the superexchange interaction. It has been shown that antiferromagnetism is destroyed by doping with about 15% of holes for t/J=10. The results are discussed in the light of recent experiments for high Tc oxides.