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 hat around the (pi,0), (0,pi) 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.