Spin depolarization dynamics of WSe_2 bilayer

In this work, the spin dynamics of a centrosymmetric WSe_2 bilayer has been investigated by the two-color timeresolved Kerr rotation together with helicity-resolved transient reflectance techniques. Two depolarization processes associated with the direct transition are discovered at a low temperature of 10 K, with the characteristic decaying time of～3.8 ps and ～20 ps, respectively. The short decay time of ～3.8 ps is suggested to be the exciton spin lifetime of the WSe_2 bilayer, which is limited by the short exciton lifetime of the WSe_2 bilayer and the rapid intervalley electron–hole exchange interaction between K+and K-valley in the same layer as that of monolayer. The long decay time of ～20 ps is suggested to be the spin lifetime of photo-excited electrons, whose spin relaxation is governed by the rapid intervalley scattering from the K valley to the global minimum Σ valley and the subsequent interlayer charge transfer in WSe_2 bilayer.Our experimental results prove the existence of the spin-polarized excitons and carriers even in centrosymmetric transition metal dichalcogenides(TMDCs) bilayers, suggesting their potential valleytronic and spintronic device applications.