Charged exciton kinetics in monolayer MoSe2 near ferroelectric domain walls in periodically

Monolayers of semiconducting transition metal dichalcogenides are a strongly emergent platform for exploring quantum phenomena in condensed matter, building novel opto-electronic devices with enhanced functionalities. Due to their atomic thickness, their excitonic optical response is highly sensitive to their dielectric environment. In this work, we explore the optical properties of monolayer thick MoSe2 straddling domain wall boundaries in periodically poled LiNbO3. Spatially-resolved photoluminescence experiments reveal spatial sorting of charge and photo-generated neutral and charged excitons across the boundary. Our results reveal evidence for extremely large in-plane 1 ar X iv :2 01 0. 01 41 6v 1 [ co nd -m at .m es -h al l] 3 O ct 2 02 0 electric fields of 3000 kV/cm at the domain wall whose effect is manifested in exciton dissociation and routing of free charges and trions toward oppositely poled domains and a non-intuitive spatial intensity dependence. By modeling our result using driftdiffusion and continuity equations, we obtain excellent qualitative agreement with our observations and have explained the observed spatial luminescence modulation using realistic material parameters. For integrated opto-electronic and quantum photonic devices, the ability to combine different materials having complementary functionalities is key to achieving high performance. Two-dimensional (2D) transition metal dichalcogenides (TMDs), having the chemical formula MX2 (M=Mo,W and X=Se,S), are of strong current interest since they are direct gap semiconductors in the monolayer form, with bandgaps that are tunable throughout the visible spectral range. They host strongly bound excitons (Bohr radii aB ∼ 1.1-1.8 nm, binding energy Eb ∼ 300-500meV)1 that remain stable up to room temperature2. Moreover, they can be readily van-der-Walls bonded onto a wide range of different substrates3. Unlike conventional semiconductors, the atomic thickness and 2D nature of TMDs is such that their properties change depending on the substrate onto which they are placed. This opens up new routes to tailor the exciton energy landscape by intentionally placing TMDs onto substrates with spatially varying dielectric properties4–8. For example, lateral quantum confinement can enhance quasiparticle correlations, opening the way to study collective behaviour and many-body physics9–15. While dielectric engineering is sufficient for trapping neutral excitonic complexes, the manipulation of free-charges and charged excitons and the exciton ionization needed for efficient photodetection requires strong electric fields16–19. Gate tunable devices with e.g. nanoscale metallic contacts can result in strain fields and large Schottky barrier heights. Moreover, proximity-induced electric fields arising from Fermi-level pinning produce band bending and local potential barrier in the TMD18,20. As such, new approaches are needed to produce high electric fields over lengthscales comparable to the exciton Bohr radius. Lithium niobate is an