Electronic excitations in Bi₂Sr₂ CaCu₂O₈: Fermi surface, dispersion, and absence of bilayer splitting

From a detailed study, including polarization dependence, of the normal state angle-resolved photoemission spectra for Bi₂Sr₂CaCu₂O₈, we find only one CuO₂ band related feature. All other spectral features can be ascribed either to umklapps from the superlattice or to “shadow bands.” Even though the dispersion of the peaks looks like band theory, the line shape is anomalously broad and no evidence is found for bilayer splitting. We argue that the “dip feature” in the spectrum below T_c arises not from bilayer splitting, but rather from many-body effects.