2020/04/15 by Fanyao Qu, Helena Bragança, Railson Vasconcelos +3 · 1 citation
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.mtrl-sci
paper · pdf · doi:10.1088/2053-1583/ab2cf7
published as 2D Materials 6.4 (2019): 045014
arxiv created 2020/04/15 · arxiv updated 2020/04/17
We developed a comprehensive theoretical framework focusing on many-body effects of exciton species in monolayer WS2, including bright and dark excitons, and intra- and inter-valley biexcitons, to investigate valley dynamics in monolayer WS2 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.