MOMENTUM DEPENDENCE OF THE SPIN AND CHARGE EXCITATIONS IN THE 2-DIMENSIONAL HUBBARD-MODEL

The low energy spin and charge excitations in the 2D Hubbard model nea r half filling are analyzed. The RPA spectra derived from inhomoheneou s mean field textures are analyzed. Spin excitations show a commensura te peak at half filling, incommensurate peaks near half filling, and a broad background typical of a dilute Fermi liquid away from half fill ing. Charge excitations, near half filling, are localized near (0,0), and they occupy a small portion of the Brillouin Zone, in a way consis tent with the existence of a small density of carriers, and a small Fe rmi surface. At higher hole densities, they fill the entire BZ, and ca n be understood in terms of a conventional Fermi liquid picture. The r esults are consistent with the observed features of the high-T-c super conductors.