Special features in photoemission from the s-p bands of copper

Angle-resolved photoemission (ARPES) studies of the (100) face of clean copper using He I radiation reveal two distinct peaks with binding energies between 0 and 2 eV. These peaks have the opposite dispersion with emission angle and have very different widths, one peak in particular being unusually sharp. We show that both of these peaks are associated with the upper part of the s-p band and that their behaviour can be qualitatively explained by an examination of the bulk band structure for finite values of k_∥ away from the Δ-symmetry direction. We also show that rather good quantitative agreement with the experimental spectra can be obtained by performing realistic photocurrent calculations which include a proper treatment of the surface electronic structure, matrix elements and lifetime effects. Finally, the significance of a sharp peak arising from the s-p band for ARPES studies of random alloys and chemisorption systems is briefly discussed.