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تسجيل مستخدم جديدExciton Relaxation Cascade in Two-dimensional Transition-metal dichalcogenides
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Monolayers of transition-metal dichalcogenides (TMDs) are characterized by an extraordinarily strong Coulomb interaction giving rise to tightly bound excitons with binding energies of hundreds of meV. Excitons dominate the optical response as well as the ultrafast dynamics in TMDs. As a result, a microscopic understanding of exciton dynamics is the key for technological application of these materials. In spite of this immense importance, elementary processes guiding the formation and relaxation of excitons after optical excitation of an electron-hole plasma has remained unexplored to a large extent. Here, we provide a fully quantum mechanical description of momentum- and energy-resolved exciton dynamics in monolayer molybdenum diselenide (MoSe$_2$) including optical excitation, formation of excitons, radiative recombination as well as phonon-induced cascade-like relaxation down to the excitonic ground state. Based on the gained insights, we reveal experimentally measurable features in pump-probe spectra providing evidence for the exciton relaxation cascade.
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We present a theoretical study of the in-plane electric filed induced exciton dissociation in two dimensional (2D) transition metal dichcogenides MX$_2$ (M=Mo, W; X=S, Se). The exciton resonance states are determined from continuum states by the comp
lex coordinate rotation method with the Lagrange mesh method to solve the exciton Hamiltonian. Our results show that the exciton dissociation process can be effectively controlled by the electric field. The critical electric fields needed for ground state exciton to make the dissociation process dominating over combination processes is in the range of 73 - 91 V/$mu$m for monolayer MX$_2$. Compared with ground state exciton, the excited excitons are more easily to be dissociated due to their delocalization nature, e.g. the critical field for 2$s$ excited state is as low as 12 - 16 V/$mu$m . More importantly, we found that exciton become more susceptive to external electric field and a much smaller critical electric field is needed in the presence of a dielectric substrate and in finite-layer MX$_2$. This work may provide a promising way to enhance the exciton dissociation process and improve the performance of 2D materials based optoelectronic devices.
Transition metal dichalcogenides (TMDCs) have emerged as a new two dimensional materials field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some
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