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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
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Language:English
Date:2016
Deposited On:11 Jan 2017 17:55
Last Modified:11 Jan 2017 17:55
Publisher:American Physical Society
ISSN:0031-9007
Publisher DOI:https://doi.org/10.1103/PhysRevLett.117.277201

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