MAGNETIC-SUSCEPTIBILITY OF THE 2-DIMENSIONAL HUBBARD-MODEL - COMMENT

The observed magnetic spin susceptibility of high-temperature superconductors such as La2-xSrxCuO4 increases when x increases from zero, i.e., as one dopes away from half-filling. Recent Monte Carlo simulations of A. Moreo [Phys. Rev. B 48, 3380 (1993)] suggest that this behavior can be reproduced by the two-dimensional Hubbard model only at large coupling, namely, U/t of order 10. Using longer runs, our Monte Carlo simulations show that the same behavior as for U/t = 10 is obtained even in the intermediate coupling regime (U/t = 4), as long as the temperature is low enough (T = t/6) that strong antiferromagnetic correlations are building up at half-filling. These results are consistent with the fact that in two dimensions, the generalized random phase approximation should fail in the pa-rameter range where it predicts a magnetic phase transition.