Direct observation of spin-layer locking by local Rashba effect in monolayer semiconducting PtSe2 film

Wei Yao,Huaqing Huang,Mingzhe Yan,Wenhui Duan,Ke Deng,Yeliang Wang,Eryin Wang,Linfei Li,Koji Miyamoto,Chaoxing Liu,Shuyun Zhou,Kenan Zhang,Taichi Okuda,Hongjun Gao

doi:10.1038/ncomms14216

Abstract

The generally accepted view that spin polarization in non-magnetic solids is induced by the asymmetry of the global crystal space group has limited the search for spintronics materials mainly to non-centrosymmetric materials. In recent times it has been suggested that spin polarization originates fundamentally from local atomic site asymmetries and therefore centrosymmetric materials may exhibit previously overlooked spin polarizations. Here, by using spin- and angle-resolved photoemission spectroscopy, we report the observation of helical spin texture in monolayer, centrosymmetric and semiconducting PtSe2 film without the characteristic spin splitting in conventional Rashba effect (R-1). First-principles calculations and effective analytical model analysis suggest local dipole induced Rashba effect (R-2) with spin-layer locking: opposite spins are degenerate in energy, while spatially separated in the top and bottom Se layers. These results not only enrich our understanding of the spin polarization physics but also may find applications in electrically tunable spintronics.

Highlights

The generally accepted view that spin polarization in non-magnetic solids is induced by the asymmetry of the global crystal space group has limited the search for spintronics materials mainly to non-centrosymmetric materials
The new insight that spin polarization in non-magnetic materials originates from relativistic spin–orbit coupling (SOC) by the local asymmetry[1,2,3,4] rather than the global asymmetry has led to two forms of hidden spin polarization in centrosymmetric materials, local Rashba R-2 and local Dresselhaus D-2 effect, which are distinguished from the conventional Rashba R-15–12 and Dresselhaus D-113 effects previously discovered in non-centrosymmetric bulk materials or interfaces
Different from the R-1 effect, the R-2 effect is induced by local dipole fields and can exist in centrosymmetric materials

Summary

Introduction

The generally accepted view that spin polarization in non-magnetic solids is induced by the asymmetry of the global crystal space group has limited the search for spintronics materials mainly to non-centrosymmetric materials. By combining spin- and angle-resolved photoemission spectroscopic (spin-ARPES) measurements with three-dimensional spin analysis and theoretical calculations, we report the hidden helical spin texture and spin-layer locking induced by R-2 effect in a monolayer semiconducting PtSe2 film.

Results

Conclusion