Abstract
We report the spin-selective optical excitation of carriers in inversion-symmetric bulk samples of the transition metal dichalcogenide (TMDC) WSe_{2}. Employing time- and angle-resolved photoelectron spectroscopy (trARPES) and complementary time-dependent density functional theory (TDDFT), we observe spin-, valley-, and layer-polarized excited state populations upon excitation with circularly polarized pump pulses, followed by ultrafast (<100 fs) scattering of carriers towards the global minimum of the conduction band. TDDFT reveals the character of the conduction band, into which electrons are initially excited, to be two-dimensional and localized within individual layers, whereas at the minimum of the conduction band, states have a three-dimensional character, facilitating interlayer charge transfer. These results establish the optical control of coupled spin-, valley-, and layer-polarized states in centrosymmetric materials with locally broken symmetries and suggest the suitability of TMDC multilayer and heterostructure materials for valleytronic and spintronic device concepts.
Highlights
We report the spin-selective optical excitation of carriers in inversion-symmetric bulk samples of the transition metal dichalcogenide (TMDC) WSe2
In monolayer TMDCs, the lack of inversion symmetry in 2H polytypes gives rise to a spin-valley correlation of the band structure which, in combination with strong spin-orbit coupling in those containing heavy transition metals [5], lifts the energy degeneracy of electronic bands of opposite spin polarizations, allowing for valley-selective electronic excitation with circularly polarized light [1,2,5,6,7,8]. While such an effect should be forbidden in inversion symmetric materials, recent theoretical work suggests that the absence of inversion symmetry within moieties of the unit cell locally lifts the spin degeneracy [9,10]
The lack of inversion symmetry and the presence of in-plane dipole moments within individual TMDC layers can be seen as atomic site Dresselhaus and Rashba effects and can cause a hidden spin texture in a globally inversion symmetric material [9]
Summary
We report the spin-selective optical excitation of carriers in inversion-symmetric bulk samples of the transition metal dichalcogenide (TMDC) WSe2. Generation and Evolution of Spin-, Valley-, and Layer-Polarized Excited Carriers in Inversion-Symmetric WSe2
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