Unveiling the Hidden Spin-Polarized Bi(110) Surface States by Spin-Resolved Photoemission

This is the authors' abstract. We don't add key points for this paper.

The full three-dimensional spin texture of the Bi(110) surface states has been investigated by means of spin- and angle-resolved photoemission spectroscopy. The observed complex in-plane spin texture is in basic agreement with the prior reports and first-principles calculations, and the previously unreported out-of-plane spin polarization (PZ) is observed to be substantial. More significantly, the PZ texture exhibits an unexpected breaking of spin degeneracy at the Brillouin zone boundary, in contradiction to standard symmetry-based expectations. Our first-principles calculations reveal that the anticipated vanishing of PZ arises from the quantum interference between two surface wave functions propagating with opposite out-of-plane spin polarizations. These findings strongly suggest that the photoemission process selectively probes one of them, exposing the hidden PZ polarization of the surface wave function; i.e., the apparent spin vanishing is not due to an absence of polarization, but rather results from interference at the wave function level.