To: 15/03/2023 14:00
In this talk I will first recall briefly the general properties of 2D excitons in Transition Metal Dichalcogenides (TMD) monolayers: giant binding energy, oscillator strength, exchange interactions, spin/valley locking ...1.
Encapsulation of TMD monolayers in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogeneous exciton linewidth2,3. We have demonstrated that the exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect 4.
We also measured the exciton fine structure by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T 5,6. I will show that the bright-dark exciton splitting can be tuned by a few meV, as a result of a significant Lamb shift of the optically active exciton which arises from emission and absorption of virtual photons triggered by the vacuum fluctuations of the electromagnetic field7 .
Finally I will present recent experimental results on spin/valley pumping of resident electrons in WSe2 and WS2 monolayers8. Using a spatially-resolved optical pump-probe experiment, we measure the lateral transport of spin/valley polarized electrons over very long distances (tens of micrometers)9. These results highlight the key role played by the spin-valley locking effect in TMD monolayers on the pumping efficiency and the polarized electron transport.
1 G. Wang et al, Rev. Mod. Phys. 90, 021001 (2018)
2 F. Cadiz et al, Phys. Rev. X 7, 021026 (2017)
3 G. Wang et al, Phys. Rev. Lett. 119, 047401 (2017)
4 H. Fang et al, Phys. Rev. Lett. 123, 067401 (2019)
5 C. Robert et al, Phys. Rev. Lett . 126, 067403 (2021)
6 C. Robert et al, Nature Com. 11, 4037 (2020)
7 L. Ren et al, submitted (2023)
8 C. Robert et al, Nature Com. 12, 5455 (2021)
9 C. Robert et al, Phys. Rev. Lett. 129, 027402 (2022)