Conserving approximation for the three-band Hubbard model: Flat quasiparticle 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 conserving approximation including self-consistently the interaction with charge, spin, and particle-particle fluctuations. The dispersion of the quasiparticle peak is flat around the ({π},0), (0,{π}) points as observed in recent angle-resolved photoemission measurements. The significant reduction of the dispersion near the Fermi level is due to spin fluctuations, rather than being induced by band effects. {} 1996 The American Physical Society.