Interlayer Excitons In Heterostructures Research Articles

Photoluminescence manipulation in two-dimensional transition metal dichalcogenides

Two-dimensional transition metal dichalcogenides (TMDCs) have been regarded as an intriguing platform for exploring novel physical phenomena and optoelectronic devices due to their excitonic emission characteristics derived from the atomic thin thickness and reduced dielectric screening effect. Notably, monolayer TMDCs with a direct bandgap exhibiting strong photoluminescence (PL) are promising candidates for the light-emitting devices, while the interlayer excitons in heterostructures hold great potential for the photonic chips and optical communication applications. However, the non-ideal photoluminescent intensity and quality due to the ultrathin thickness and high defect density of experimentally obtained monolayer TMDCs limit the further development for the light-emission applications. Here, we summarize the research progress on the PL manipulation of the excitonic emission in TMDCs, where the PL intensity enhancement and emission wavelength regulation are included. The concept and characteristics of excitons are overviewed firstly, followed by the discussion on the evaluation and characterization of excitonic emission. The state-of-the-art progress on the manipulation of the neutral excitons and interlayer excitons PL are then summarized. Finally, the challenges and prospects are proposed.

Charge-charge interaction in three-layer systems: Classical approach

General explicit analytical expressions for the charge-charge interaction energy $W(Z,{Z}^{\ensuremath{'}},R)$ between two point charges in heterostructures with three plane layers were obtained in the framework of classical electrostatics, i.e., the dielectric permittivities of the constituent media were assumed to be constant. Here, $R$ is the lateral (along the interfaces) distance between the charges, and $Z$ and ${Z}^{\ensuremath{'}}$ are their normal coordinates. The obtained results may be applied to the interaction between charges for their various arrangements in the layered system. For instance, the interaction across the interlayer was calculated as the function of the dielectric constants ${\ensuremath{\varepsilon}}_{i}\phantom{\rule{0.28em}{0ex}}(i=1,2,3)$ of the constituent media. It was demonstrated that the textbook Coulomb expression is far from being valid in this case. In particular, more sophisticated formulas proposed here should be used when considering interlayer excitons in heterostructures of various kinds and electron-hole superfluidity in such sandwiches.

Long-Lived Direct and Indirect Interlayer Excitons in van der Waals Heterostructures.

We report the observation of a doublet structure in the low-temperature photoluminescence of interlayer excitons in heterostructures consisting of monolayer MoSe2 and WSe2. Both peaks exhibit long photoluminescence lifetimes of several tens of nanoseconds up to 100 ns verifying the interlayer nature of the excitons. The energy and line width of both peaks show unusual temperature and power dependences. While the low-energy peak dominates the spectra at low power and low temperatures, the high-energy peak dominates for high power and temperature. We explain the findings by two kinds of interlayer excitons being either indirect or quasi-direct in reciprocal space. Our results provide fundamental insights into long-lived interlayer states in van der Waals heterostructures with possible bosonic many-body interactions.