Experimental verification of a spin effect in photoemission: Polarized electrons due to phase-shift differences in the normal emission from Pt(100) by unpolarized radiation

A theoretical prediction of Tamura and Feder has been experimentally verified: Photoelectrons from the fourfold-symmetric surface of a centrosymmetric crystal, Pt(100), can be polarized even if the incident radiation is unpolarized and the electrons are emitted normal to the surface. For 21.2- and 16.9-eV photon energies, a spin-polarization component ${\mathit{P}}_{\mathit{y}}$ perpendicular to the reaction plane is found. The degree of polarization is up to 15% and does not change when the crystal is rotated about its surface normal. This supports strongly the prediction that the effect is due to phase-shift differences.