Valence-band and resonance-photoemission study ofLa2CuO4+xsingle crystals

Abstract

Angle-resolved resonance-photoemission measurements at 15{endash}30 and 100{endash}130 eV photon energy ranges were performed from different principal planes of La{sub 2}CuO{sub 4+x} single crystals. Resonance photoemission near the La-4d threshold shows the presence of states in the valence band associated with La within the energy region 2{endash}5.5 eV. At low photon energies near the La-5p threshold (16.5 eV) with the normal emission aligned in the (001) direction (c{perpendicular} surface), valence-band spectra display nonmonotonic photon energy dependence of a 6-eV binding-energy feature, i.e., beyond the main La density of states in the valence band. Along with the absence of such behavior for normal emission from the other principal planes (100) and (010) (c{parallel} surface geometry), this fact implies that surface termination effects need to be taken into account to explain these results. The binding energy of the resonant feature and the resonance photon energy are slightly different for photon polarization vector parallel and perpendicular to the Cu-O planes of the crystal. Measurements were also done on another La-based compound, La{sub 0.7}Sr{sub 0.3}MnO{sub 3}, having similar La-O plane but much smaller c-axis parameter. This manganese oxide demonstrates the same nonmonotonic dependence of the 6-eV binding-energy feature, but in a wider photon energy region.more » On the basis of this comparison, it is tentatively suggested that the intensity modulation is governed not only by the core-level threshold, but may carry information of bulk Brillouin zones as well. {copyright} {ital 1997} {ital The American Physical Society}« less