SKM 2023 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 2: 2D Materials and their Heterostructures II: h-BN and WSe2
DS 2.4: Vortrag
Montag, 27. März 2023, 12:15–12:30, SCH A 316
Mobile interlayer excitons at the Mott transition in Moiré-free heterostructures — •Edith Wietek1, Mikhail M. Glazov2, Matthias Florian3, Takashi Taniguchi4, Kenji Watanabe4, Alexander Steinhoff5, and Alexey Chernikov1 — 1Technische Universität Dresden — 2Sankt Petersburg — 3University of Michigan — 4NIMS, Ibaraki — 5Universität Bremen
Vertically stacked heterostructures of transition metal dichalcogenides present an exciting platform to study electronic and excitonic many-particle states. In this study we investigate propagation of excitons in these systems from low to very high densities to disentangle the effects of dipolar excitons from those stemming from moiré effects. We take advantage of hBN-encapsulated WSe2/MoSe2 heterostructures studied in the moiré-free limit of large, atomically reconstructed domains. Using ultrafast microscopy, we show that the interlayer excitons propagate freely even at cryogenic temperatures and low densities. At elevated exciton densities, we demonstrate that in addition to broadly assumed exciton-exciton repulsion, the non-linear increase of the diffusion coefficient also originates from efficient exciton-exciton annihilation. Remarkably, at the exciton ionization threshold of the Mott transition and beyond, we reveal a highly unusual regime of negative effective diffusion that persist for many 100's of ps after the excitation. This observation presents a particularly interesting case of non-equilibrium phenomena in composite many-particle systems, highlighting the rich physics of optical excitations in van der Waals heterostructures.