Observation of spin-momentum-layer locking in centrosymmetric BiOI

TL;DR

This study reveals hidden spin polarization and spin-layer locking in the centrosymmetric layered material BiOI, challenging traditional views and providing insights for future spintronic device design.

Contribution

It demonstrates the existence of spin-layer locking in a centrosymmetric crystal and elucidates the microscopic mechanism behind spin, momentum, and layer interactions.

Findings

Spin polarization is highly polarized along the Brillouin zone boundary.

Spin polarization vanishes around the zone center due to nonsymmorphic structure.

Hidden spin polarization can exist in centrosymmetric materials.

Abstract

Spin polarization effects in nonmagnetic materials are generally believed as an outcome of spin-orbit coupling provided that the global inversion symmetry is lacking, also known as 'spin-momentum locking'. The recently discovered hidden spin polarization indicates that specific atomic site asymmetry could also induce measurable spin polarization, leading to a paradigm shift to centrosymmetric crystals for potential spintronic applications. Here, combining spin- and angle-resolved photoemission spectroscopy and theoretical calculations, we report distinct spin-layer locking phenomena surrounding different high-symmetry momenta in a centrosymmetric, layered material BiOI. The measured spin is highly polarized along the Brillouin zone boundary, while is almost vanishing around the zone center due to its nonsymmorphic crystal structure. Our work not only demonstrates the existence of hidden spin polarization, but also uncovers the microscopic mechanism of the way spin, momentum and layer locking to each other, shedding lights on the design metrics for future spintronic devices.