Electronic band structure of Cu3Au: An angle-resolved photoemission study along the [111]-direction

High-resolution normal photoemission (ARPE) spectra have been recorded for Cu₃Au(111) with the use of polarized synchrotron and rare-gas resonance radiation in the photon energy range from 9 to 27 eV. It is for the first time that dispersions of the gold-like bands have been found experimentally. Using a fully relativistic layer-KKR photoemission formalism, occupied and unoccupied bands as well as one-step-model photoemission spectra have been calculated. The comparison of calculated spectra with experimental ones and the observation of direct-transition resonances upon photon energy near the Brillouin zone-center reveal a shift of the unoccupied ground-state bands by about +2.5 eV (self-energy shift). The direct-transition structures in the experimental spectra have been exploited to determine the dispersions of the occupied bands along the [111] direction (A line in k space). In order to determine the wave vector of the experimental direct transitions we used as final state that calculated unoccupied band along [111], which also exists in pure copper and gold up to about 20 eV above the Fermi energy (“unfolded” band structure), shifted by + 2.5 eV. The experimental occupied bands with Cu character are in very good agreement with theory after shifting the latter by about 0.3 eV to lower energy, whereas somewhat bigger discrepancies exist for the gold-like bands.