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Preprints
169. F. Tagarelli, E. Lopriore, D. Erkensten, R. Perea-Causin, S. Brem, J. Hagel, Z. Sun, G. Pasquale, K. Watanabe, T. Taniguchi, E. Malic, A. Kis, "Electrical control of hybrid exciton transport in a van der Waals heterostructure", arXiv: 2303.00419
Interactions between out-of-plane dipoles in bosonic gases enable the long-range propagation of excitons. The lack of direct control over collective dipolar properties has hitherto limited the degrees of tunability and the microscopic understanding of exciton transport. In this work, we modulate the layer hybridization and interplay between many-body interactions of excitons in a van der Waals heterostructure with an applied vertical electric field. By performing spatiotemporally resolved measurements supported by microscopic theory, we uncover the dipole-dependent properties and transport of excitons with different degrees of hybridization. Moreover, we find constant emission quantum yields of the transporting species as a function of excitation power with dominating radiative decay mechanisms over nonradiative ones, a fundamental requirement for efficient excitonic devices. Our findings provide a complete picture of the many-body effects in the transport of dilute exciton gases and have crucial implications for the study of emerging states of matter, such as Bose-Einstein condensation, as well as for optoelectronic applications based on exciton propagation.
arXiv: 2303.00419168. R. Rosati, I. Paradisanos, L. Huang, Z. Gan, A. George, K. Watanabe, T. Taniguchi, L. Lombez, P. Renucci, A. Turchanin, B. Urbaszek, E. Malic, "Interface engineering of charge-transfer excitons in 2D lateral heterostructures", arXiv: 2302.02617
The existence of bound charge transfer (CT) excitons at the interface of monolayer lateral heterojunctions has been debated in literature, but contrary to the case of interlayer excitons in vertical heterostructure their observation still has to be confirmed. Here, we present a microscopic study investigating signatures of bound CT excitons in photoluminescence spectra at the interface of hBN-encapsulated lateral MoSe2-WSe2 heterostructures. Based on a fully microscopic and material-specific theory, we reveal the many-particle processes behind the formation of CT excitons and how they can be tuned via interface- and dielectric engineering. For junction widths smaller than the Coulomb-induced Bohr radius we predict the appearance of a low-energy CT exciton. The theoretical prediction is compared with experimental low-temperature photoluminescence measurements showing emission in the bound CT excitons energy range. Our joint theory-experiment study presents a significant step towards a microscopic understanding of optical properties of technologically promising 2D lateral heterostructures.
arXiv: 2302.02617167. Q. Lin, H. Fang, Y. Liu, Y. Zhang, M. Fischer, J. Li, J. Hagel, S. Brem, E. Malic, N. Stenger, Z. Sun, M. Wubs, S. Xiao, "A room-temperature moiré interlayer exciton laser" arXiv: 2302.01266
Moiré superlattices in van der Waals heterostructures offer highly tunable quantum systems with emergent electronic and excitonic properties such as superconductivity, topological edge states, and moiré-trapped excitons. Theoretical calculations predicted the existence of the moiré potential at elevated temperatures; however, its impact on the optical properties of interlayer excitons (IXs) at room temperature is lacking, and the benefits of the moiré effects for lasing applications remain unexplored. We report that the moiré potential in a molybdenum disulfide/tungsten diselenide (MoS2/WSe2) heterobilayer system can significantly enhance light emission, elongate the IX lifetime, and modulate the IX emission energy at room temperature. By integrating a moiré superlattice with a silicon topological nanocavity, we achieve ultra-low-threshold lasing at the technologically important telecommunication O-band thanks to the significant moiré modulation. Moreover, the high-quality topological nanocavities facilitate the highest spectral coherence of < 0.1 nm linewidth among all reported two-dimensional material-based laser systems. Our findings not only open a new avenue for studying correlated states at elevated temperatures, but also enable novel architectures for integrated on-chip photonics and optoelectronics.
arXiv: 2302.01266166. C. Linderälv, J. Hagel, S. Brem, E. Malic, P. Erhart, "The moiré potential in twisted transition metal dichalcogenide bilayers", arXiv: 2205.15616
Moiré superlattices serve as a playground for emerging phenomena, such as localization of band states, superconductivity, and localization of excitons. These superlattices are large and are often modeled in the zero-angle limit, which obscures the effect of finite twist angles. Here, by means of first-principles calculations we quantify the twist-angle dependence of the moiré potential in the MoS homobilayer and identify the contributions from the constituent elements of the moiré potential. Furthermore, by considering the zero-angle limit configurations, we show that the moiré potential is rather homogeneous across the transition metal dichalcogenides (TMDs) and briefly discuss the separate effects of potential shifts and hybridization on the bilayer hybrid excitons. We find that the moiré potential in TMDs exhibits both an electrostatic component and a hybridization component, which are intertwined and have different relative strengths in different parts of the Brillouin zone. The electrostatic component of the moiré potential is a varying dipole field, which has a strong twist angle dependence. In some cases, the hybridization component can be interpreted as a tunneling rate but the interpretation is not generally applicable over the full Brillouin zone.
arXiv: 2205.15616