Many-body theory of the electronic structures in ultrathin transition-metal films: bcc Co(001)

An exact solution of a two-site crystal model with periodic boundary conditions, a two-layer {001} film with body-centered-cubic (bcc) crystalline structure, is presented for cobalt. The object is to study the many-body electronic structures of highly correlated metallic ultrathin epitaxial films. Surface effects and the confinement of the particle motion in an essentially two-dimensional layer are found to have an important influence on the electronic structures. A realistic local-density-approximation one-electron spectrum and an intrasite electron-electron interaction of full generality are used. The crystal field and the single-particle electronic structure in the bcc cobalt film are discussed. The many-body energy spectrum, the ground-state magnetization, the average magnetization and total electronic energy as a function of temperature, and the photoemission and inverse photoemission spectra are calculated. Some interesting many-body-effect-induced features are found and discussed. Physical conclusions about the many-body states in ultrathin bcc cobalt films are drawn.