Spin depolarization dynamics of WSe₂ bilayer

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.