CONSERVING APPROXIMATION FOR THE 3-BAND HUBBARD-MODEL - FLAT QUASI-PARTICLE DISPERSION

It is shown that the low-energy single-particle spectrum of the three- band Hubbard model at finite hole dopings agrees remarkably well with quantum Monte Carlo and experimental data within the framework of a co nserving approximation including self-consistently the interaction wit h charge, spin, and particle-particle fluctuations. The dispersion of the quasiparticle peak is hat around the (pi,0), (0,pi) points as obse rved in recent angle-resolved photoemission measurements. The signific ant reduction of the dispersion near the Fermi level is due to spin fl uctuations, rather than being induced by band effects.