Controlling valley splitting and Polarization of dark- and bi-excitons in monolayer WS${}_2$ by a tilted magnetic field

Abstract

We developed a comprehensive theoretical framework focusing on many-body effects of exciton species in monolayer WS${}_2$, including bright and dark excitons, and intra- and inter-valley biexcitons, to investigate valley dynamics in monolayer WS${}_2$ subjected to a tilted magnetic field B. In particular, the evolution of the exciton population densities and the many-body particle scatterings are considered to calculate the valley polarization (V P ) as a function of the magnetic field. We found valley splittings for the dark exciton and biexciton energy levels that are larger than those of bright excitons, of -0.23 meV/T. For example, -0.46 meV/T for dark excitons and -0.69 meV/T for bright-dark intra-valley biexcitons. Furthermore, inter-valley bright-dark excitons have an opposite valley energy splittings of +0.23 meV/T. For the samples pumped by linearly polarized light, V P exhibits distinct magnetic field dependence for different types of many-body particle states. Among them, the V P of the intra-valley bright-dark biexcitons increases with increasing magnetic field and reaches nearly 50% at B=65 T. The brightened dark exciton, on the other hand, exhibits vanishing VP, indicating long valley relaxation time. Remarkably, the inter-valley bright-dark biexciton shows unconventional behavior with an inverted VP. The opposite VP for intra- and inter-valley bright-dark biexcitons, coupled with their large valley splitting and long valley lifetime may facilitate their coherent manipulation for quantum computing.

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Cited by in corpus (5)

• Magnetically tunable exciton valley coherence in monolayer WS${}_2$ mediated by the electron-hole exchange and exciton-phonon interactions
• Laser-field detuning assisted optimization of exciton valley dynamics in monolayer WSe${}_2$: Geometric quantum speed limit
• Spin/Valley pumping of resident electrons in WSe2 and WS2 monolayers
• Wannier Excitons Confined in Hexagonal Boron Nitride Triangular Quantum Dots
• Ellipticity-Controlled Bright-Dark Coherence Transition in Monolayer WSe2