Spin Polarization in Cu Core-Level Photoemission with Linearly Polarized Soft X Rays

We report on the first observation of electron spin polarization in photoemission from inner shells of a nonmagnetic solid with linearly polarized radiation. The effect is observed in normal emission from the $2p$ and $3p$ core levels of Cu(001) excited with $p$-polarized soft-x-ray radiation at oblique incidence. We interpret the effect in terms of spin-orbit interaction and interference of continuum partial waves. The results are relevant for the understanding of magnetic dichroism and spin polarization in core-level photoemission from ferromagnets.