Quasiparticle interference scattering of spin-polarized Shockley-like surface state electrons: Ni(111)

We report on a detailed quasiparticle interference (QPI) scattering study of the Ni(111) surface by low-temperature scanning tunneling spectroscopy (LT-STS). While conventional constant-separation STS shows two broad features, which are interpreted as the ${\ensuremath{\Lambda}}_{3}$ bulk band and $sp$-like Shockley-type surface state ($sp$-SS), energy-dependent Fourier-transformed QPI maps reveal the band dispersion of the underlying surface electronic features. We find two electronlike branches in the $sp$-SS dispersion, which are interpreted as the exchange-split minority and majority spin part. The exchange splitting is determined to $\ensuremath{\Delta}{E}_{\mathrm{ex}}=100\ifmmode\pm\else\textpm\fi{}8$ meV. In addition, a holelike $d$-derived surface resonance is found. Band onsets and effective electron masses are determined by fitting the band dispersion with a parabola at small $k$ values. Hybridization effects with bulk electronic states are observed towards larger $k$ values. Prominent quantum confinement phenomena of the $sp$-SS are observed in STS data obtained within vacancy islands. The results can be interpreted within a one-dimensional quantum-well model.