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

Methods to generate spin-polarized electronic states in nonmagnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices(1). This is generally accepted to require breaking global structural inversion symmetry(1-5). In contrast, here we report the observation from spin- and angle-resolved photoemission spectroscopy of spin-polarized bulk states in the centrosymmetric transition-metal dichalcogenide WSe2. Mediated by a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localized(6), we show how spin splittings up to similar to 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(7,8), of key importance for using these compounds in proposed valleytronic devices.