Direct observation of local Rashba spin polarization and spin-layer locking in centrosymmetric monolayer PtSe$_2$

TL;DR

This study demonstrates that centrosymmetric monolayer PtSe₂ exhibits local Rashba spin polarization and spin-layer locking, challenging the traditional view that spin polarization requires global inversion asymmetry, with implications for spintronics.

Contribution

It provides experimental evidence of local Rashba effect and spin-layer locking in a centrosymmetric material, supported by first-principles calculations and analytical modeling.

Findings

Centrosymmetric PtSe₂ shows helical spin texture due to local Rashba effect.

Opposite spin polarizations are degenerate but spatially separated in layers.

Results suggest potential for electrically tunable spintronic applications.

Abstract

The generally accepted view that spin polarization is induced by the asymmetry of the global crystal space group has limited the search for spintronics [1] materials to non-centrosymmetric materials. Recently it has been suggested that spin polarization originates fundamentally from local atomic site asymmetries [2], and therefore centrosymmetric materials may exhibit previously overlooked spin polarizations. Here by using spin- and angle-resolved photoemission spectroscopy (spin-ARPES), we report helical spin texture induced by local Rashba effect (R-2) in centrosymmetric monolayer PtSe$_2$ film. First-principles calculations and effective analytical model support the spin-layer locking picture: in contrast to the spin splitting in conventional Rashba effect (R-1), the opposite spin polarizations induced by R-2 are degenerate in energy while spatially separated in the top and bottom Se layers. These results not only enrich our understanding of spin polarization physics, but also may find applications in electrically tunable spintronics.