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O: Fachverband Oberflächenphysik

O 22: 2D Materials II: Electronic Structure (joint session O/TT)

O 22.6: Talk

Tuesday, March 19, 2024, 12:00–12:15, MA 005

Ultrafast Hidden Spin Polarization Dynamics of Bright and Dark Excitons in 2H-WSe2 — •Mauro Fanciulli1,2, David Bresteau2, Jérome Gaudin3, Shuo Dong4, Romain Géneaux2, Thierry Ruchon2, Olivier Tcherbakoff2, Jan Minar5, Olivier Heckmann1,2, Maria Christine Richter1,2, Karol Hricovini1,2, and Samuel Beaulieu31LPMS, CY Cergy Paris Université, 95031 France — 2Université Paris-Saclay, CEA, CNRS, LIDYL, 91191 France — 3Université de Bordeaux - CNRS - CEA, CELIA, 33405 France — 4Beijing National Laboratory for Condensed Matter Physics, 100190 China — 5University of West Bohemia, 30100 Czech Republic

We performed spin-, time- and angle-resolved extreme ultraviolet photoemission spectroscopy of excitons prepared by photoexcitation of inversion-symmetric 2H-WSe2 with circularly polarized light.

The very short probing depth of XUV photoemission permits selective measurement of photoelectrons originating from the top-most WSe2 layer, allowing for direct measurement of hidden spin polarization of bright and momentum-forbidden dark excitons.

Our results reveal efficient chiroptical control of bright excitons' hidden spin polarization. Following optical photoexcitation, intervalley scattering between nonequivalent K-K' valleys leads to a decay of bright excitons' hidden spin polarization. Conversely, the ultrafast formation of momentum-forbidden dark excitons acts as a local spin polarization reservoir, which could be used for spin injection in van der Waals heterostructures involving multilayer transition metal dichalcogenides.

Keywords: TMDC; spin; dynamics; excitons; photoemission

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