INTRINSIC LAMBDA-1-SYMMETRY SURFACE-STATE ON CO(0001)

An intrinsic surface state on Co(0001) has been found using angle-resolved photoemission with synchrotron radiation which has an energy of Ei=-0.3 eV at » (zone center) relative to the Fermi energy EF. Its symmetry has been determined to be of 1 character using measurements with s- and p-polarized radiation. Its momentum dispersion (E vs k,) and h 1/2-dependent photoionization cross section have also been determined. At the zone center », the surface state lies in an absolute energy gap just above the uppermost 3, d-like (Ei=-0.35 eV) bulk state, well above the uppermost sp-like 1 state (Ei=-1.15 eV), and below occupied 3 d-like bulk states near (energies between Ei=-0.05 eV and 0). As previously reported for Ni, this surface state is extremely sensitive to absorbates and significantly affects field emission, spin-polarized photoemission, chemisorption, etc. for Co(0001). © 1979 The American Physical Society.