Spin-polarized photoelectrons excited by circularly polarized radiation from a nonmagnetic solid.

Abstract

We report a spin analysis of core-level photoelectrons excited by circularly polarized x rays from a nonmagnetic solid. In a combined experimental and theoretical study, we show that the spin-orbit-split W 4 f 7/2 and 4 f 5/2 photoemission lines from W~110! exhibit high spin polarizations of opposite sign that vary with energy and emission direction. These results suggest the study of the magnetic structure of nonmagnetic/ferromagnetic interfaces formed on high-atomic-number substrates by spin-polarized photoelectron diffraction. Photoelectrons from unpolarized atoms can be highly spin polarized when ejected by circularly polarized ~CP! light, due to the Fano effect: 1~a! although the dipole operator does not act upon the electron spin explicitly, the photon angular momentum is partially transferred to the photoelectron spin by the spin-orbit ~SO! interaction. Shortly after its prediction in 1969, this effect was observed in the valence levels of alkali-metal 1~b! and rare-gas atoms 2 in gaseous and solid-state phases, and today it is well known as the basic mechanism behind the GaAs source for spin-polarized electrons. 3 In particular, photoelectrons excited by CP light from p, d, and f shells can acquire substantial spin polarization over a wide photon energy range. 4 Up to now, the spin analysis of photoelectrons from unpolarized targets has mostly served fundamental interests of ~i! understanding photoemission ~PE! dynamics through quantum mechanically ‘‘complete’’ experiments 5,6 and ~ii! characterizing the symmetry of valence bands in nonmagnetic solids. 7