Partial spectral weights of disordered Cu-Au alloys

We present valence-band photoemission spectra of polycrystalline CuxAu1-x (x=0.10, 0.25, 0.50, 0.75, 0.90) disordered binary alloys taken with variable incident-photon energies using synchrotron radiation. Taking advantage of the Cooper minimum phenomenon of the Au 5d band and taking proper account of the photoionization matrix element, we obtain experimental partial spectral weights for the alloys determined from the measured ratio of Au 5d and Cu 3d photoionization cross sections. We find that the Au partial density of states in dilute Au alloys is very strongly hybridized with the Cu host band and its bandwidth is not much reduced, contrary to the conclusion of some earlier work which claimed that the Au states have a greatly narrowed bandwidth due to the band repulsion between different d bands. Our finding is consistent with recent theoretical results. The lattice relaxation effect on the electronic structures of Cu-Au alloys is also investigated using ultraviolet photoemission spectroscopy. Compared with the bandwidths of ordered alloys which do not suffer lattice relaxation, those of disordered alloys are reduced by a small amount, which can be interpreted as the result of both the total volume change and the lattice relaxation effects, whose magnitudes are comparable.