Excitation energy map of high-energy dispersion anomalies in cuprates
The anomalous high-energy dispersion of the conductance band in the high-T-c superconductor Bi(Pb)(2)Sr2CaCu2O8+delta (Pb-Bi2212) has been extensively mapped by angle-resolved photoemission spectroscopy as a function of excitation energy in the range from 34 to 116 eV. Two distinctive types of dispersion behavior are observed around 0.6 eV binding energy, which alternate as a function of photon energy. The continuous transitions observed between the two kinds of behavior near 50, 70, and 90 eV photon energies allow one to exclude the possibility that they originate from the interplay between the bonding and antibonding bands. The effects of three-dimensionality can also be excluded as a possible origin of the excitation energy dependence, as the large period of the alterations is inconsistent with the lattice constant in this material. We therefore confirm that the strong photon energy dependence of the high-energy dispersion in cuprates originates mainly from the photoemission matrix element that suppresses the photocurrent in the center of the Brillouin zone.