Layer-dependent band dispersion and correlations using tunable soft X-ray ARPES

Soft X-ray Angle-Resolved Photoemission Spectroscopy is applied to study in-plane band dispersions of nickel as a function of probing depth. Photon energies between hnu = 190 and 780 eV were used to effectively probe up to similar to 3-7 layers (similar to 5-12 Angstrom). The results show layer-dependent band dispersion of the Delta(21) minority spin band which crosses the Fermi level in 3 or more layers, in contrast to the known top 1-2 layers dispersion obtained using ultra-violet rays. The layer dependence corresponds to an increased value of exchange splitting and suggests reduced-correlation effects in the bulk compared to the surface.