Direct observation of spin-polarised bulk bands in an inversion-symmetric semiconductor

TL;DR

This study provides direct experimental evidence of significant spin polarisation in bulk states of an inversion-symmetric semiconductor, revealing local inversion asymmetry effects that enable spin manipulation in such materials.

Contribution

It demonstrates the existence of strong spin polarisation in centrosymmetric WSe₂ due to local structural asymmetries, confirming the 'hidden' spin polarisation theory in inversion-symmetric materials.

Findings

Observed spin polarisation up to ~0.5 eV in bulk WSe₂

Identified local inversion asymmetry as the cause of spin splitting

Revealed complex spin textures modulated in real and momentum space

Abstract

Methods to generate spin-polarised electronic states in non-magnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices. This is generally accepted to require breaking global structural inversion symmetry. In contrast, here we present direct evidence from spin- and angle-resolved photoemission spectroscopy for a strong spin polarisation of bulk states in the centrosymmetric transition-metal dichalcogenide WSe$_2$. We show how this arises due to a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localised, leading to enormous spin splittings up to $\sim\!0.5$ eV, with a spin texture that is strongly modulated in both real and momentum space. As well as providing the first experimental evidence for a recently-predicted `hidden' spin polarisation in inversion-symmetric materials, our study sheds new light on a putative spin-valley coupling in transition-metal dichalcogenides, of key importance for using these compounds in proposed valleytronic devices.