EXCHANGE SPLITTING OF SP-LIKE SURFACE-STATES ON NI(001)

Spin-resolved inverse photoemission is employed to investigate crystal-induced and image-potential surface states on Ni(001). The observed value of the spin splitting for the crystal-induced state at XBAR is 180 +/- 60 meV and there is experimental evidence of a nonvanishing exchange splitting of the image-potential state at GAMMABAR. These data are consistently described within the framework of a multiple-reflection model for surface states if the upper band-gap boundaries are assumed to be exchange split by 200 meV at GAMMABAR and 230 meV at XBAR. For GAMMABAR, this splitting was confirmed experimentally by spin-resolved target-current spectroscopy.