Electronic spectra and their relation to the (pi,pi) collective mode in high-T-c superconductors

The photoemission line shape near (pi, 0) in Bi2Sr2CaCu2O8+delta below T-c is characterized by a sharp peak, followed at higher energy by a dip and hu mp. We study the evolution of this line shape as a function of momentum, te mperature, and doping. We find the hump scales with the peak and persists a bove T-c in the pseudogap state. We present strong evidence that the peak-d ip-hump structure arises from the interaction of electrons with a collectiv e mode of wave vector (pi, pi). The inferred mode energy and its doping dep endence agree well with a magnetic resonance observed by neutron scattering .