Anomalous S-like dispersion of in-gap single-particle excitations in the pseudogap state of cuprate superconductors

The single-particle excitations which control the opening of the pseudogap in the cuprate superconductors at some temperature T are considered to derive their specific local spectral features from resonant pairing, whereby charge carriers get momentarily trapped on dynamically deformable molecular Cu-O-Cu clusters. We show how such local excitations evolve into overdamped modes with a characteristic "S"-like dispersion around the Fermi energy, as one passes below T. This feature should be detectable in a "momentum distribution curve" angle-resolved photoemission spectroscopy analysis and help to elucidate the kind of pairing in the cuprates. Our study is based on a generic boson-fermion model for resonant pairing and is an extension of our previous dynamical mean-field theory study [A. Romano and J. Ranninger, Phys. Rev. B 62, 4066 2000] of the spectral properties of the pseudogap state.