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Valleys, defined as maxima or minima in the energy-momentum relation where carriers reside isolated by momentum mismatch, present a promising material degree of freedom, akin to electron charge or spin. Despite early theoretical interest, practical utilization of valleys has been hindered by the challenge of measurable valley contrast in natural systems. The advent of two- dimensional (2D) materials, particularly transition metal dichalcogenides (TMDs), has revolutionized valleytronics due to their intrinsic valley contrast. Specifically, monolayer TMDs exhibit a direct band gap, enabling straightforward access to valley degrees of freedom via photoluminescence experiments and valley-contrasting optical selection rules (see inset in Fig. 1 (a)). Circularly polarized photons can selectively address each valley type, with emitted photons being circularly polarized as well retaining valley information. Although significant advances have been made in addressing, reading out, and tuning valley degrees of freedom, these processes remain challenging, requiring sophisticated and costly experiments. The optical addressability of valleys in 2D TMDs holds potential for integration with nanophotonics, such as resonant nanoantennas and structured light. This talk will present a comprehensive experimental and numerical study of a hybrid system where valley-polarized photoluminescence from a MoS2 monolayer is coupled with a plasmonic nanosphere (see Fig. 1 (a)), aiming to refine simulation approaches and enhance understanding of nanoscale light-matter interactions. Additionally, the talk will explore the interaction of vortex beams with valley excitons, examining valley depolarization effects, and the potential for directional exciton transport (see Fig. 1 (b)). Figure 1 Optically pumped hybrid system consisting of a gold nanoparticle resonantly interacting with photoluminescence emitted by a monolayer MoS2. Inset: valley-contrasting optical selection rules. (b) Circularly polarized vortex beam incident on a monolayer TMD transfers momentum to valley excitons.

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Zlata Fedorova, Uni. Jena
Seminar Room of the Institute of Physics II
Contact: Erwann/Matteo