  Manipulation of spin and valley degrees of freedom is a key step towards
realizing novel quantum technologies, for which atomically thin transition
metal dichalcogenides (TMDCs) have been established as promising candidates. In
monolayer TMDCs, the lack of inversion symmetry gives rise to a spin-valley
correlation of the band structure allowing for valley-selective electronic
excitation with circularly polarized light. Here we show that, even in
centrosymmetric samples of 2H-WSe2, circularly polarized light can generate
spin-, valley- and layer-polarized excited states in the conduction band.
Employing time- and angle-resolved photoemission spectroscopy (trARPES) with
spin-selective excitation, the dynamics of valley and layer pseudospins of the
excited carriers are investigated. Complementary time-dependent density
functional theory (TDDFT) calculations of the excited state populations reveal
a strong circular dichroism of the spin-, valley- and layer-polarizations and a
pronounced 2D character of the excited states in the K valleys. We observe
scattering of carriers towards the global minimum of the conduction band on a
sub-100 femtosecond timescale to states with three-dimensional character
facilitating inter-layer charge transfer. Our results establish the optical
control of coupled spin-, valley- and layer-polarized states in centrosymmetric
materials and suggest the suitability of TMDC multilayer materials for
valleytronic and spintronic device concepts.
