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arXiv · 1505.07127

Bright and dark singlet excitons via linear and two-photon spectroscopy in monolayer transition-metal dichalcogenides

Timothy C. Berkelbach·Mark S. Hybertsen·David R. Reichman
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Abstract

We discuss the linear and two-photon spectroscopic selection rules for spin-singlet excitons in monolayer transition-metal dichalcogenides. Our microscopic formalism combines a fully $k$-dependent few-orbital band structure with a many-body Bethe-Salpeter equation treatment of the electron-hole interaction, using a model dielectric function. We show analytically and numerically that the single-particle, valley-dependent selection rules are preserved in the presence of excitonic effects. Furthermore, we definitively demonstrate that the bright (one-photon allowed) excitons have $s$-type azimuthal symmetry and that dark $p$-type excitons can be probed via two-photon spectroscopy. The screened Coulomb interaction in these materials substantially deviates from the $1/\varepsilon_0 r$ form; this breaks the "accidental" angular momentum degeneracy in the exciton spectrum, such that the 2$p$ exciton has a lower energy than the 2$s$ exciton by at least 50 meV. We compare our calculated two-photon absorption spectra to recent experimental measurements.

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Timothy C. Berkelbach, Mark S. Hybertsen, David R. Reichman. 2015-08-11. Bright and dark singlet excitons via linear and two-photon spectroscopy in monolayer transition-metal dichalcogenides. https://doi.org/10.1103/physrevb.92.085413

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