We report the direct observation of intervalley exciton between the Q conduction valley and Γ valence valley in bilayer WSe2 by photoluminescence. The QΓ exciton lies at ~18 meV below the QK exciton and dominates the luminescence of bilayer WSe2. By measuring the exciton spectra at gate-tunable electric field, we reveal different interlayer electric dipole moments and Stark shifts between QΓ and QK excitons. Notably, we can use the electric field to switch the energy order and dominant luminescence between QΓ and QK excitons. Both QΓ and QK excitons exhibit pronounced phonon replicas, in which two-phonon replicas outshine the one-phonon replicas due to the existence of (nearly) resonant exciton-phonon scatterings and numerous two-phonon scattering paths. We can simulate the replica spectra by comprehensive theoretical modeling and calculations. The good agreement between theory and experiment for the Stark shifts and phonon replicas strongly supports our assignment of QΓ and QK excitons.
@article{arxiv.2101.11161,
title = {Electric-field-tunable intervalley excitons and phonon replicas in bilayer WSe$_2$},
author = {Mashael M. Altaiary and Erfu Liu and Ching-Tarng Liang and Fu-Chen Hsiao and Jeremiah van Baren and Takashi Taniguchi and Kenji Watanabe and Nathaniel M. Gabor and Yia-Chung Chang and Chun Hung Lui},
journal= {arXiv preprint arXiv:2101.11161},
year = {2021}
}