PUB - Publikationen an der Universität Bielefeld

The conserving and self-consistent fluctuation-exchange approximation is used to calculate the quasi-particle self-energy and the dynamic spin susceptibility for the two-dimensional Hubbard model at band-fillings n somewhat below half-filling (n = 1). The spectral density of the spin susceptibility exhibits incommensurate peaks similar to those observed by neutron scattering in La2-xSrxCuO4. No spin-density-wave instability is found down to the lowest temperatures T (greater than or similar to 40 K) and up to the largest n (less than or similar to 0.85) and couplings U/t (less than or similar to 5) treated in this paper. For the same parameter space we calculate the eigenvalues of the superconducting eigen-solutions with d-wave and extended s-waves symmetry. These eigenvalues increase as T is decreased and n is increased, however, they are always far below unity which means that one is far from a superconducting transition. The calculated normal-state quantities are in qualitative agreement with the measured quantities of the cuprates, for example, the electrical resistivity is nearly a linear function of T like that of YBa2Cu3O7.