Matrix-element induced spin polarization of photoelectrons from bulk bands

TL;DR

This paper demonstrates the extension of soft X-ray photoelectron spectroscopy to include spin resolution, revealing matrix-element induced spin polarization effects in bulk tungsten, marking a significant advancement in bulk photoemission studies.

Contribution

It introduces a method to measure spin polarization in bulk materials using circularly polarized X-rays, highlighting the detection of interference effects at X-ray energies for the first time.

Findings

Detection of optical spin-orientation effects at X-ray energies

Observation of interference of final-state partial waves in spin polarization

Extension of spin-resolved photoemission techniques to bulk materials

Abstract

Angular- or $k$-resolved photoelectron spectroscopy in the soft X-ray range gives access to the bulk electronic structure of materials. Here this technique is extended to the spin degree of freedom. A non-magnetic material (tungsten) was chosen, in order to exclude any initial-state spin polarization from exchange-split bands. By measurement of two spin-polarizations for different light helicity, one can distinguish between contributions of optical spin-orientation by circularly-polarized X-rays (Fano componen) and a second component originating from interference of final-state partial waves. Both phenomena have so far only been observed at low photon energies. Their detection in the X-ray range is a milestone on the way to the "complete experiment" in bulk photoemission.