Observation of bright exciton splitting in strained WSe2 monolayers

Abstract

High-resolution magnetophotoluminescence measurements of strained WSe 2 monolayers are reported. At low temperature, a splitting of a few meV in the neutral exciton peak is observed, which is attributed to the theoretically predicted in-plane (xy) anisotropy splitting. Measurements in high magnetic fields up to 30 T demonstrate that strain and intervalley electron-hole exchange mix the valley-exciton energy levels, leading to a relaxation of the valley-selective optical selection rules and to strongly modified exciton g factors. Our observation of the bright exciton splitting provides crucial information about the dispersion of valley excitons and paves the way to develop valley functionality for photonic devices.

Anomalous rotation of the linearly polarized emission of bright excitons in strained WSe2 monolayers under high magnetic fields

“…WSe 2 monolayer flakes were prepared by mechanical exfoliation from bulk crystals and transferred onto 285nm SiO 2 /Si substrates. The monolayer region was confirmed by concomitant high-resolution polarized-resolved μ-Raman, μ-PL, and μ-PL excitation (μ-PLE) measurements at liquid-He temperature [21]. The strain in our monolayer samples is unintentional and is likely created during the exfoliation process.…”

“…The strain in our monolayer samples is unintentional and is likely created during the exfoliation process. Mechanical stretching in one direction leads to uniaxial strain, which is enhanced during cooling the monolayer sample, because of the different thermal expansion coefficients of the lattices of the TMDC monolayer and the underlying SiO 2 substrate [21]. The distinction between strained and unstrained monolayer samples was made by using μ-Raman spectroscopy measurements (see Ref.…”

“…The distinction between strained and unstrained monolayer samples was made by using μ-Raman spectroscopy measurements (see Ref. [21]). Figure 1(a) illustrates the schematics of the optical setup in a high magnetic field.…”

“…Moreover, the energy separation between the indirect and direct gaps increases due to suppression of the phonon-induced intervalley (K-Q) scattering [20]. At cryogenic temperatures, when the exciton linewidth is smaller due to a reduced phononassisted broadening, a splitting of the bright exciton emission into two exciton components, each with peculiar polarization properties, is observed [21]. In this respect, probing linear polarization of neutral exciton emission in strained monolayer TMDCs under high magnetic fields can provide important information regarding the mechanism of valley decoherence.…”

Orthogonally Polarized Luminescence of Single Bismuth Phosphate Microcrystal Doped with Europium

“…structures from 0D quantum dots to 2D atomic thin films, depending on their anisotropic nature. [10][11][12][13][14][15][16][17][18][19][20] Compared with these structures, rareearth dopants in micro/nanocrystals, benefitting from the unique and sheltered 4f N electronic configurations, exhibit some unique properties, such as multiple-wavelength emission, long-lived coherence, and excellent photostability at room temperature. [21][22][23][24] Although the suitable site symmetries of the crystal can endow the doped elements with the polarized emissions, [25] measurements are usually performed on bulk or powder states in which a lot of small particles have independently random orientations, thus resulting in unpolarized luminescence.…”