VALENCE-BAND AND RESONANCE-PHOTOEMISSION STUDY OF LA2CUO4-CRYSTALS(X SINGLE)

Angle-resolved resonance-photoemission measurements at 15-30 and 100-1 30 eV photon energy ranges were performed from different principal pla nes of La2CuO4+x single crystals. Resonance photoemission near the La- 4d threshold shows the presence of states in the valence band associat ed with La within the energy region 2-5.5 eV. At low photon energies n ear the La-Sp threshold (16.5 eV) with the normal emission aligned in the (001) direction (c perpendicular to surface), valence-band spectra display nonmonotonic photon energy dependence of a 6-eV binding-energ y feature, i.e., beyond the main La density of states in the valence b and. Along with the absence of such behavior for normal emission from the other principal planes (100) and (010) (c parallel to surface geom etry), this fact implies that surface termination effects need to be t aken into account to explain these results. The binding energy of the resonant feature and the resonance photon energy are slightly differen t for photon polarization vector parallel and perpendicular to the Cu- O planes of the crystal. Measurements were also done on another La-bas ed compound, La0.7Sr0.3MnO3, having similar La-O plane but much smalle r c-axis parameter. This manganese oxide demonstrates the same nonmono tonic dependence of the 6-eV binding-energy feature, but in a wider ph oton energy region. On the basis of this comparison, it is tentatively suggested that the intensity modulation is governed not only by the c ore-level threshold, but may carry information of bulk Brillouin zones as well.