Abstract
Frequency-dependent dielectric constant dispersion of monolayer WSe2, ε(ω)=ε1(ω)+iε2(ω), was obtained from simultaneously measured transmittance and reflectance spectra. Optical transitions of the trion as well as A-, B-, and C-excitons are clearly resolved in the ε2 spectrum. A consistent Kramers-Kronig transformation between the ε1 and ε2 spectra support the validity of the applied analysis. It is found that the A- and B-exciton splitting in the case of the double-layer WSe2 can be attributed to the spin-orbit coupling, which is larger than that in the monolayer WSe2. In addition, the temperature-induced evolution of the A-exciton energy and its width are explained by model equations with electron-phonon interactions.
Highlights
In contrast to graphene and boron nitride that can be categorized as a gapless Dirac material and wide gap insulator, respectively [1,2], transition-metal dichalcogenides (TMDCs) such as
Several works have reported on the determination of the dielectric constant of monolayer TMDCs based on their reflectance and transmittance [18,19]
We report on the frequency-dependent dielectric constants of monolayer WSe2
Summary
In contrast to graphene and boron nitride that can be categorized as a gapless Dirac material and wide gap insulator, respectively [1,2], transition-metal dichalcogenides (TMDCs) such asMoS2, MoSe2, WS2, and WSe2, are semiconducting layered materials. The dielectric constant and effective mass are still the most deterministic factors for the binding energy of two-dimensional (2D) monolayer excitons. Though the ellipsometry technique is used to obtain complex dielectric constants of monolayer MoS2 and WSe2 [14,15,16], it requires dispersion modeling, and has difficulty in performing microscopic measurements.
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