Enhanced spin polarization of conduction electrons in Ni explained by comparison with Cu

Abstract

The spin-split Fermi-level crossings of the conduction band in Ni are mapped out by high-resolution photoemission and compared to the equivalent crossing in Cu. The area of the quasiparticle peak decreases rapidly below ${E}_{F}$ in Ni, but not in Cu. Majority spins have larger spectral weight at ${E}_{F}$ than minority spins, thereby enhancing the spin polarization beyond that expected from the density-of-states. A large part of the effect can be traced to a rapid variation of the matrix element with k at the point where the $s,p$ band begins to hybridize with the ${d}_{z}^{2}$ state. However, it is quite possible that the intensity drop in Ni is reinforced by a transfer of spectral weight from single-particle to many-electron excitations. The results suggest that the matrix element should be considered for explaining the enhanced spin polarization observed for Ni in spin-polarized tunneling.