Out-of-plane orbital characters of intrinsic and doped holes in La2-xSrxCuO4

Bulk-sensitive, polarization-dependent oxygen K- and copper L-edge absorption spectra of single-domain La2-xSrxCuO4 with CuO2 planes tilted off the sample surface were measured. A novel experimental configuration was utilized to achieve complete polarization geometry and eliminate optical path variations. Contrary to previous measurements, our data show for both intrinsic and doped holes a significant amount of O2pz character, likely associated with apical O, but a very weak Cu3d3z2-r2 character. The quantitative results impose strong contraints on superconductivity models invoking out-of-plane orbitals, and suggest that the apical O 2pz orbital may play an important role in high-Tc phenomena