Twisted layers of atomically thin two-dimensional materials realize a broad range of novel quantum materials with engineered optical and transport phenomena arising from spin and valley degrees of freedom and strong electron correlations in hybridized interlayer bands. Here, we report experimental and theoretical studies of WSe2 homobilayers obtained in two stable configurations of 2H (60∘ twist) and 3R (0∘ twist) stackings by controlled chemical vapor synthesis of high-quality large-area crystals. Using optical absorption and photoluminescence spectroscopy at cryogenic temperatures, we uncover marked differences in the optical characteristics of 2H and 3R bilayer WSe2 which we explain on the basis of beyond-DFT theoretical calculations. Our results highlight the role of layer stacking for the spectral multiplicity of momentum-direct intralayer exciton transitions in absorption, and relate the multiplicity of phonon sidebands in the photoluminescence to momentum-indirect excitons with different spin valley and layer character. Our comprehensive study generalizes to other layered homobilayer and heterobilayer semiconductor systems and highlights the role of crystal symmetry and stacking for interlayer hybrid states.
@article{arxiv.2112.08994,
title = {Stacking-dependent exciton multiplicity in WSe$_2$ bilayers},
author = {Zhijie Li and Jonathan Förste and Kenji Watanabe and Takashi Taniguchi and Bernhard Urbaszek and Anvar S. Baimuratov and Iann C. Gerber and Alexander Högele and Ismail Bilgin},
journal= {arXiv preprint arXiv:2112.08994},
year = {2022}
}