Direct observation of spin-valley-layer locking in centrosymmetric bulk WSe$_2$ by spin- and angle-resolved photoemission

Methods to generate spin-polarized 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, I will report our observation from spin- and angle-resolved photoemission spectroscopy of spin-polarized bulk states in the centrosymmetric transition-metal dichalcogenide 2H-WSe$_2$ [1]. Mediated by a lack of inversion symmetry in constituent Se-W-Se monolayers of the bulk crystal where the electronic states are localized, we show how enormous spin splittings up to $\sim\!0.5$~eV result, with a spin texture that is strongly modulated in both real and momentum space. Through this, our study provides direct experimental evidence for a putative locking of the spin with the layer and valley pseudospins in transition-metal dichalcogenides, of key importance for using these compounds in proposed valleytronic devices. \\[4pt] [1] J.M.~Riley {\it et al.}, Nature Phys. {\bf 10} (2014) 835