ANGLE-RESOLVED PHOTOEMISSION EXPERIMENTS ON BI2SR2CACU2O8+DELTA(001) - EFFECTS OF THE INCOMMENSURATE LATTICE MODULATION

Core-level X-ray photoelectron-diffraction patterns have been measured from cleaved Bi2Sr2CaCu2O8+delta (001) surfaces for all elements present in this compound. The incommensurate modulation along b ([010]) leads to a strong inequivalence of a- and b-directions for Bi, Sr and Cu photoelectrons, while Ca and O emission show less effect. Ultraviolet-photoemission experiments recording the emission intensity at the Fermi energy over a large solid angle are also presented, providing a direct mapping of the Fermi surface. A c(2 x 2) superstructure is observed on the Fermi surface suggesting antiferromagnetic correlations within the Cu-O planes. The effects of the lattice modulation are clearly observable at the Fermi energy, and they are enhanced for binding energies higher than a few tens of meV.