Charged excitons in monolayer WSe2 : Experiment and theory

Abstract

Charged excitons, or X ± -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 WSe2 monolayers encapsulated in hexagonal boron nitride, to investigate the difference in binding energy between X + and X − and the X − 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 − is observed. We present a symmetry analysis of the different X + and X − 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 − trions as well as the fine structure of the X − state can be related to the short-range Coulomb exchange interaction between the charge carriers. arXiv:1705.02110v2 [cond-mat.mes-hall] 9 May 2018

Radially polarized light beams from spin-forbidden dark excitons and trions in monolayer WSe2

“…The bright negative trion (X − ) and the dark negative trion (X − d ) generate the highest energy lines in the electron-doped ML. The observed fine structure splitting of the bright negative trion confirms the high quality of our sample [31]. All measured energies agree well with previous reports on excitonic states in WSe 2 MLs encapsulated with h-BN [34,35,53,54].…”

Dark excitations in monolayer transition metal dichalcogenides

“…The excitations discussed above have been proposed previously on the basis of model calculations [24,32]. Employing ab initio methods [28,29], we are now able to provide a quantitative prediction of the energy and relative ordering of these excitations, treating dark and bright excitons and is observed 30 meV above.…”

Wigner crystals in two-dimensional transition-metal dichalcogenides: Spin physics and readout

“…3(c)] lattices with a lattice constant a. Here we consider ∆ 0 = 0, which corresponds to a wavelength λ ∼ (700 − 800) nm in state-of-the-art TMD setups [46,47]. We choose θ such that the cross section of the Gaussian beam is small enough and does not exceed the size of the WC.…”