Zlata Fedorova

---

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.

---

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