EMISSION OF CORRELATED ELECTRON PAIRS FOLLOWING SINGLE-PHOTON ABSORPTION BY SOLIDS AND SURFACES

The simultaneous emission of two electrons from condensed matter follo wing the absorption of a linearly polarized photon is studied in the f irst order-perturbation theory for the radiation field, and within the dipole approximation. The double emission from localized and delocali zed electronic states is considered. It is shown that spectra of the e mitted pairs obey propensity rules expressed by the scalar product of the center-of-mass vector momentum of the pair and the photon's polari zation vector. Furthermore, it is shown that diffraction of the pair f rom the lattice occurs when the pair's center-of-mass wave vector chan ges by a lattice reciprocal vector during the photoemission. For semi- infinite solids with delocalized valence electrons, an initial state i s constructed from single-particle orbitals. Following the absorption of the photon the valence-band electron pair propagates into the vacuu m within the screened electron-electron Coulomb potential. Numerical r esults for a clean Cu crystal are analyzed for photon polarization par allel and perpendicular to the surface. [S0163-1829(98)09439-9].