Anomalous Surface-State Penetration near a Band Edge

High-resolution angle-resolved photoemission studies of a potassium-doped Cu (111) surface have allowed extraction of the zone-center $\mathrm{sp}$ surface-state evanescent decay length as a function of energy location in the $L_{2^{\prime }}-L_1$ projected band gap. The results are well matched by recent first-principles calculations, but are in quantitative discord with expectations based on complex band structures extrapolated from bulk band calculations. Possible sources of this disagreement, including interference from final-state effects and surface-induced perturbations on bulk bands, are discussed.