Surface electronic structure of calcium, strontium, and barium

The density of surface states in Ca, Sr, and Ba is determined by x-ray-induced photoemission. Surface-related peaks at 0.6 and 1.6 eV (Ca), 0.5 and 1.4 eV (Sr), and 0.35 and 1.0 eV (Ba) below the Fermi level $E_F$ are identified. The bandwidth in Ca and Ba narrows by ∼20% at the surface. Self-consistent pseudopotential calculations for a seven-layer slab of Ca (111) and Ca (001) give the surface density of states in good agreement with experiment. The high-lying surface peak at ($E_F-0.6\mathrm{}$) eV can be identified with a band of surface states which exists both at the (111) and the (001) surface. It has a dangling-bond-like character. The peak at ($E_F-1.6\mathrm{}$) eV can be identified with a band of surface states which is found at the (001) surface. Its charge density is localized in cavity regions near the surface formed by the first and second atomic layer. Both surface bands are found in energy gaps of the projected bulk band structure.