D. Lagarde

Giant enhancement of the optical second-harmonic emission of WSe(2) monolayers by laser excitation at exciton resonances.

Monolayers (MLs) of MoS2 and WSe2 are 2D semiconductors with strong, direct optical transitions that are governed by tightly Coulomb bound eletron-hole pairs (excitons). The optoelectronic properties of these transition metal dichalcogenides are directly related to the inherent crystal inversion symmetry breaking. It allows for efficient second harmonic generation (SHG) and is at the origin of chiral optical selections rules, which enable efficient optical initialization of electrons in specific K-valleys in momentum space. Here we demonstrate how these unique non-linear and linear optical properties can be combined to efficiently prepare exciton valley coherence and polarization through resonant pumping of an excited exciton state. In particular a new approach to coherent alignment of excitons following two-photon excitation is demonstrated. We observe a clear deviation of the excited exciton spectrum from the standard Rydberg series via resonances in SHG spectroscopy and two- and one-photon absorption. The clear identification of the 2s and 2p exciton excited states combined with first principle calculations including strong anti-screening effects allows us to determine an exciton binding energy of the order of 600 meV in ML WSe2.

Valley dynamics probed through charged and neutral exciton emission in monolayer WSe 2

Optical interband transitions in monolayer transition metal dichalcogenides such as WSe2 and MoS2 are governed by chiral selection rules. This allows efficient optical initialization of an electron in a specific K valley in momentum space. Here we probe the valley dynamics in monolayer WSe2 by monitoring the emission and polarization dynamics of the well-separated neutral excitons (bound electron-hole pairs) and charged excitons (trions) in photoluminescence. The neutral exciton photoluminescence intensity decay time is about 4 ps, whereas the trion emission occurs over several tens of ps. The trion polarization dynamics shows a partial, fast initial decay within tens of ps before reaching a stable polarization of ≈20%, for which a typical valley polarization decay time of the order of 1 ns can be inferred.

Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides

We study the neutral exciton energy spectrum fine structure and its spin dephasing in transition metal dichalcogenides such as MoS

Exciton radiative lifetime in transition metal dichalcogenide monolayers

_2

Room-temperature defect-engineered spin filter based on a non-magnetic semiconductor

. The interaction of the mechanical exciton with its macroscopic longitudinal electric field is taken into account. The splitting between the longitudinal and transverse excitons is calculated by means of the both electrodynamical approach and

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

\mathbf k \cdot \mathbf p

Surfactant-free CZTS nanoparticles as building blocks for low-cost solar cell absorbers

perturbation theory. This long-range exciton exchange interaction can induce valley polarization decay. The estimated exciton spin dephasing time is in the picosecond range, in agreement with available experimental data.

Reduction of defect density by rapid thermal annealing in GaAsBi studied by time-resolved photoluminescence

We have investigated the exciton dynamics in transition metal dichalcogenide monolayers using time-resolved photoluminescence experiments performed with optimized time resolution. For

Full Electrical Control of the Electron Spin Relaxation in GaAs Quantum Wells

\mathrm{MoS}{\mathrm{e}}_{2}

Electron spin dynamics and g-factor in GaAsBi

monolayer, we measure