Complex band structure and surface state penetration of Cu (111).

High resolution angle-resolved photoemission studies of a potassium- doped Cu(111) surface have allowed extraction of the zone-center sp surface state evanescent decay length as a function of energy location in the L(2), - L(1), projected band gap. This yields the complex band structure over a limited energy range. The results are in quantitative accord with recent first-principles calculations, and in qualitative accord with expectations based on nearly-free-electron and effective mass theory. The quantitative disagreement with these is discussed.