Charged excitons in monolayer WSe 2 : Experiment and theory

By E. Courtade, M. Semina, M. Manca, M. Glazov, C. Robert, F. Cadiz, Gang Wang, Takashi Taniguchi, Kenji Watanabe, M. Pierre and 6 more. 2017

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Charged excitons, or ${X}^{\ifmmode\pm\else\textpm\fi{}}$ trions, in monolayer transition-metal dichalcogenides have binding energies of several tens of meV. Together with the neutral exciton ${X}^{0}$ they dominate the emission spectrum at low and elevated temperatures. We use charge-tunable devices based on ${\mathrm{WSe}}_{2}$ monolayers encapsulated in hexagonal boron nitride to investigate the difference in binding energy between ${X}^{+}$ and ${X}^{\ensuremath{-}}$ and the ${X}^{\ensuremath{-}}$ fine structure. We find in the charge-neutral regime, the ${X}^{0}$ emission accompanied at lower energy by a strong peak close to the longitudinal optical (LO) phonon energy. This peak is absent in reflectivity measurements, where only the ${X}^{0}$ and an excited state of the ${X}^{0}$ are visible. In the $n$-doped regime, we find a closer correspondence between emission and reflectivity as the trion transition with a well-resolved fine-structure splitting of 6 meV for ${X}^{\ensuremath{-}}$ is observed. We present a symmetry analysis of the different ${X}^{+}$ and ${X}^{\ensuremath{-}}$ trion states and results of the binding energy calculations. We compare the trion binding energy for the $n$- and $p$-doped regimes with our model calculations for low carrier concentrations. We demonstrate that the splitting between the ${X}^{+}$ and ${X}^{\ensuremath{-}}$ trions as well as the fine structure of the ${X}^{\ensuremath{-}}$ state can be related to the short-range Coulomb-exchange interaction between the charge carriers.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/ed2d2cdb39413a90becf4cd1baa791a1f72ba73c

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In Materials Chemistry

  1. Jinbo Pang

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