Generation and evolution of spin-, valley-, and layer-polarized excited carriers in inversion-symmetric $WSe_2$

Bertoni, R; Nicholson, C W; Waldecker, L; Hübener, H; Monney, C; De Giovannini, U; Puppin, M; Hoesch, M; Springate, E; Chapman, R T; Cacho, C; Wolf, M; Rubio, A; Ernstorfer, R (2016). Generation and evolution of spin-, valley-, and layer-polarized excited carriers in inversion-symmetric $WSe_2$. Physical Review Letters, 117(27):277201.

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.

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.

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Item Type: Journal Article, refereed, original work 07 Faculty of Science > Physics Institute 530 Physics English 2016 11 Jan 2017 17:55 19 Aug 2018 06:30 American Physical Society 0031-9007 Green https://doi.org/10.1103/PhysRevLett.117.277201 : FunderFP7: Grant ID622934: Project TitleOPTCHATRA - Optical charge transfer processes in early stages of photosynthesis from first-principle computational techniques: FunderSNSF: Grant IDPZ00P2_154867: Project TitleTime- and angle-resolved photoemission spectroscopy on correlated materials