We discuss the application of the multiple scattering theory to obtain first-principles predictions of angle-resolved photoemission intensities (ARPES) in the high-Tc superconductors. In this connection, we have generalized and implemented the ‘one-step’ photoemission approach to treat systems with an arbitrary number of atoms in the layer unit cell. We illustrate the methodology with results for the r-S symmetry direction for the (001)-surface of orthorhombic YBa2Cu3O7. Our computations give insight into the effects of surface termination, and of polarization of incident light on photoemission intensities.

We discuss positron annihilation (2D-ACAR) measurements in the c-projection on an untwinned metallic single crystal of YBa2Cu3O7-x as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a ‘background corrected’ experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displaysin particular clear signatures of the electron ridge Fermi surface.