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arXiv · 2306.03610

Ultrafast Hidden Spin Polarization Dynamics of Bright and Dark Excitons in 2H-WSe$_2$

Mauro Fanciulli·David Bresteau·Jérome Gaudin·Shuo Dong·Romain Géneaux·Thierry Ruchon·Olivier Tcherbakoff·Ján Minár·Olivier Heckmann·Maria Christine Richter·Karol Hricovini·Samuel Beaulieu
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Abstract

We performed spin-, time- and angle-resolved extreme ultraviolet photoemission spectroscopy (STARPES) of excitons prepared by photoexcitation of inversion-symmetric 2H-WSe$_2$ with circularly polarized light. The very short probing depth of XUV photoemission permits selective measurement of photoelectrons originating from the top-most WSe$_2$ 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.

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Mauro Fanciulli, David Bresteau, Jérome Gaudin, Shuo Dong, Romain Géneaux, Thierry Ruchon, Olivier Tcherbakoff, Ján Minár, Olivier Heckmann, Maria Christine Richter, Karol Hricovini, Samuel Beaulieu. 2023-07-18. Ultrafast Hidden Spin Polarization Dynamics of Bright and Dark Excitons in 2H-WSe$_2$. https://doi.org/10.1103/physrevlett.131.066402

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