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In this work, a hybrid structure of multilayer transition-metal dichalcogenides (TMDs) and a ferroelectric polymer is designed to achieve passive control of optical properties in situ. The electrical polarization in the ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer can regulate the photoluminescence (PL) in bilayer WSe 2 . The total PL emission intensity is substantially suppressed or enhanced under large gate voltage in bilayer WSe 2 . This is because electrons transfer between the conduction band K valley and the conduction band Λ valley by the electrostatic field in the P(VDF-TrFE) polymer. This electron transfer further adjusts the proportion of direct and indirect excitons and, in turn, changes the overall optical radiation efficiency. We also illustrate that the engineered PL originates from the external electric-field-dependent transferred electron effect. The theoretical result matches the experimental data well. This work demonstrates a device platform in which passive regulation is achieved using 2D TMDs modulated by polarized ferroelectric materials.

Cysteine-capped cadmium selenide/cadmium sulfide (CdSe/CdS) dot/rod nanocrystals (NCs) were synthesized and then doped in poly(vinyl alcohol) (PVA) films. Compared with an L-/D-cysteine-capped NC solution (10 -4 ), the anisotropic factors of the circular dichroism and circular polarized luminescence in the doped PVA films increased by one order of magnitude, probably because of the enhanced anisotropy degree, crystal orientations, and ordered morphologies. The two- and three-photon absorption coefficients of the doped PVA films were determined as 0.58 cm/GW at 800 nm and 2.3×10 -4   cm 3 /GW 2 at 1300 nm, respectively. The chiral NC-doped PVA films are promising for applications in chirality-related nonlinear photonic devices.

We report the observation of anomalously robust valley polarization and valley coherence in bilayer WS2. The polarization of the photoluminescence from bilayer WS2 follows that of the excitation source with both circular and linear polarization, and remains even at room temperature. The near-unity circular polarization of the luminescence reveals the coupling of spin, layer, and valley degree of freedom in bilayer system, and the linearly polarized photoluminescence manifests quantum coherence between the two inequivalent band extrema in momentum space, namely, the valley quantum coherence in atomically thin bilayer WS2. This observation provides insight into quantum manipulation in atomically thin semiconductors.

In monolayer group-VI transition metal dichalcogenides, charge carriers have spin and valley degrees of freedom, both associated with magnetic moments. On the other hand, the layer degree of freedom in multilayers is associated with electrical polarization. Here we show that transition metal dichalcogenide bilayers offer an unprecedented platform to realize a strong coupling between the spin, valley and layer pseudospin of holes. Such coupling gives rise to the spin Hall effect and spin-dependent selection rule for optical transitions in inversion symmetric bilayer and leads to a variety of magnetoelectric effects permitting quantum manipulation of these electronic degrees of freedom. Oscillating electric and magnetic fields can both drive the hole spin resonance where the two fields have valley-dependent interference, making an interplay between the spin and valley as information carriers possible for potential valley-spintronic applications. We show how to realize quantum gates on the spin qubit controlled by the valley bit.