OUT-OF-PLANE ORBITAL CHARACTERS OF INTRINSIC AND DOPED HOLES IN LA2-XSRXCUO4

Bulk-sensitive, polarization-dependent O K- and Cu 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 0 2p(z) character, likely associated with apical O, but a very weak Cu 3d3z2-r2 character. These results impose strong constraints on superconductivity models invoking out-of-plane orbitals, and suggest that the apical O 2p(z) orbital may play an important role in high-T(c) phenomena.