new paper: Bertoni et al., Physical Review Letters 117, 277201 (2016).

A range of transition metal dichalcogenides (TMDCs) are semiconductors with layered crystalline structure. In the form of monolayers, these TMDCs are 2D materials with peculiar optoelectronic properties and an unusual spin texture of the electronic structure, i.e. a spin-valley correlation. In contrast, bilayers and bulk crystals of 2H-WSe₂ are centrosymmetric, which causes all electronic states to be spin-degenerate. We show, however, that spin-polarized excited carriers can be generated in bulk crystals of the non-magnetic layered material WSe₂. This is a consequence of the hidden spin polarization in this class of materials: optical excitations generates excited states with 2D character, i.e. localized to an individual layer in the crystal. The broken atomic-site asymmetry (within each layer) dominates over the symmetry of the unit cell (consisting of two-layers) and results in spin-polarized excited states, which are additionally localized in real and reciprocal space. This finding suggests the suitability of semiconducting TMDCs for spintronic applications.