Photoemission above the Fermi Level: The Top of the MinoritydBand in Nickel

Abstract

The magnetic phase transition in nickel metal has been studied with high resolution photoemission spectroscopy. A monochromatized high intensity He $I\alpha$ photon source provides access to the dispersion of thermally populated states up to ${5k}_{B}T$ above the Fermi level. On Ni(111) the coalescence of the partially occupied minority $d$ band and the occupied majority $d$ band is observed in raising the temperature above the Curie point. Close to a fast dispersing $\mathrm{sp}$ band anomalously high intensity from the minority $d$ band is found. This is a clue that $\mathrm{sp}-d$ fluctuations at the Fermi level are a driving force in the magnetic phase transition.