Polarization-dependent photoemission studies of the electronic structure of La2CuO4+x single crystals

Recently we have reported the first resonance photoemission results on cleaved single crystal superconductor La2CuO4+x using excitation energies below 20 eV at a temperature of about 30 K [1]. Spectral enhancement of the valence region of 6 eV binding energy (BE) at photon energies around 17 eV were found to be consistent with autoionization resonance excitations. We now present new polarization-dependent angle-resolved UPS results on the resonances. Two distinct features of different symmetry character are resolved and they resonate with similar intensity. The atomic origin of the resonances is discussed and our findings impose some important questions which band structure calculations for high temperature superconductors will have to address. (orig.)