Narrow antiadiabatic peak in optimally doped and underdoped high-Tc superconductors

We study the effect of antiferromagnetic (AF) correlations in the three-band Emery model, with respect to the experimental situation in weakly underdoped and optimally doped BSCCO. In the vicinity of the vH singularity of the conduction band there appears a central peak in the middle of a pseudogap, due to an antiadiabatic quasiparticle, which is insensitive to the energy scale of the mechanism responsible for the pseudogap. We find a quantum low-temperature regime, in which the pseudogap profile is created by zero-point motion of the magnons. Detailed analysis of the spectral functions along the (π,0)-(π,π) line shows significant agreement with experiment. We conclude that optimally doped BSCCO has a well-developed pseudogap of the order of 1000 K. This is only masked by the antiadiabatic quasiparticle, which provides the experimentally observed small binding energy scale.