Spin depolarization dynamics of WSe2 bilayer**Project supported by the National Natural Science Foundation of China (Grant No. 11474276) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDPB0603).

Abstract

In this work, the spin dynamics of a centrosymmetric WSe2 bilayer has been investigated by the two-color time-resolved 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 WSe2 bilayer, which is limited by the short exciton lifetime of the WSe2 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 WSe2 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.