2-DIMENSIONAL HUBBARD-MODEL - METAL-INSULATOR-TRANSITION STUDIED BY MONTE-CARLO CALCULATION

The Hubbard model on a square lattice in the ground state is investigated. Various aspects of Mott transition at half-filling are clarified from the quantum Monte Carlo study. Critical exponents of the transition for charge and spin correlations are estimated. For the doping concentration delta, the charge susceptibility is proportional to delta-1 indicating the divergence of charge mass for delta-->0, while the spin susceptibility is always finite and not singular near delta=0. Several theoretical consequences of the above results are discussed. Incommensurate peak amplitude of spin correlation scales as (delta-delta(c))-1 with delta(c)<0.01 in disagreement with RPA results in (delta-delta(c)). The antiferromagnetic order at the half-filling also shows strong correlation character and is not sensitive to the shape of the fermi surface, while the incommensurate peak observed away from the half-filling is sensitively suppressed by the loss of partial nesting consistently with the weak coupling picture. Comparisons with experimental indications of high-T(c) oxides are made.