Hauptinhalt
Veröffentlichungen 2025
209. D. Schmitt, J. P. Bange, W. Bennecke, G. Meneghini, A. AlMutairi, M.Merboldt, J. Pöhls, K. Watanabe, T. Taniguchi, S. Steil, D. Steil, R. T. Weitz, S. Hofmann, S. Brem, G. S. Matthijs Jansen, E. Malic, S. Mathias and M. Reutzel "Ultrafast nano-imaging of dark excitons", Nature Photonics 19, 187 (2025)
The role and impact of spatial heterogeneity in two-dimensional quantum materials represents one of the major research quests regarding the future application of these materials in optoelectronics and quantum information science. In the case of transition-metal dichalcogenide heterostructures, in particular, direct access to heterogeneities in the dark-exciton landscape with nanometer spatial and ultrafast time resolution is highly desired, but remains largely elusive. Here, we introduce ultrafast dark field momentum microscopy to spatio-temporally resolve dark exciton formation dynamics in a twisted WSe2/MoS2 heterostructure with 55 femtosecond time- and 500~nm spatial resolution. This allows us to directly map spatial heterogeneity in the electronic and excitonic structure, and to correlate these with the dark exciton formation and relaxation dynamics. The benefits of simultaneous ultrafast nanoscale dark-field momentum microscopy and spectroscopy is groundbreaking for the present study, and opens the door to new types of experiments with unprecedented spectroscopic and spatiotemporal capabilities.
Nature Photonics 19, 187 (2025)208. J. Jasiński, J. Hagel, S. Brem, E. Wietek, T. Taniguchi, K. Watanabe, A. Chernikov, N. Bruyant, M. Dyksik, A. Surrente, M. Baranowski, D. K. Maude, E. Malic, P. Płochocka "Quadrupolar Excitons in MoSe2 Bilayers", Nature Communications 16, 1382 (2025)
The quest for platforms to generate and control exotic excitonic states has greatly benefited from the advent of transition metal dichalcogenide (TMD) monolayers and their heterostructures. Among the unconventional excitonic states, quadrupolar excitons - a hybridized combination of two dipolar excitons with anti-aligned dipole moments - are of great interest for applications in quantum simulations and for the investigation of many-body physics. Here, we unambiguously demonstrate for the first time in natural MoSe2 homobilayers the emergence of quadrupolar excitons, whose energy shifts quadratically in electric field. In contrast to, so far reported trilayer systems hosting quadrupolar excitons, MoSe2 homobilayers have many advantages, a stronger interlayer hybridization, cleaner potential landscapes and inherent stability with respect to moiré potentials or post-stacking reconstruction. Our experimental observations are complemented by many-particle theory calculations offering microscopic insights in the formation of quadrupole excitons. Our results suggest TMD homobilayers as ideal platform for the engineering of excitonic states and their interaction with light and thus candidate for carrying out on-chip simulations.
Nature Communications 16, 1382 (2025)207. G. Lo Gerfo Morganti, R. Rosati, G. D. Brinatti Vazquez, S. Varghese, D. Saleta Reig, E. Malic, N. F. van Hulst and K.-J. Tielrooij “Transient ultrafast and negative diffusion of charge carriers in suspended MoSe2 from multilayer to monolayer”, Nature Communications 16, 5184 (2025)
Understanding the ultrafast transport properties of charge carriers in transition metal dichalcogenides is essential for advancing technologies based on these materials. Here, we study MoSe2 crystals with thicknesses down to the monolayer, combining ultrafast spatiotemporal microscopy and quantitative microscopic modelling. Crucially, we obtain the intrinsic ultrafast transport dynamics by studying suspended crystals that do not suffer from detrimental substrate effects. In mono- and bilayer crystals, we identify four sequential transport regimes. The first two regimes involve high-energy non-thermalized and quasi-thermalized carriers that propagate rapidly with diffusivities up to 1000 cm2/s. After ~1.5 ps, a remarkable third regime occurs with apparent negative diffusion, finally followed by exciton propagation limited by trapping into defect states. Interestingly, for trilayer and thicker crystals, only the first and last regimes occur. This work underscores the role of traps and dielectric environment in electron transport, offering valuable insights for the development of (flexible) (opto)electronic applications.
Nature Communications 16, 5184 (2025)206. M. Dyksik, M. Baranowski, J. J. P. Thompson, Z. Yang, M. Rivera Medina, M. Antonietta Loi, E. Malic, and P. Plochocka "Steric Engineering of Exciton Fine Structure in 2D Perovskites", Advanced Energy Materials 15, 9 (2025)
A comprehensive study of excitonic properties of 2D layered perovskites is provided, with an emphasis on understanding and controlling the exciton fine structure. First, an overview of the optical properties is presented, discussing the challenges in determining the bandgap and exciton binding energies. Through magneto-optical spectroscopic measurements (up to B = 140 T), scaling laws are established for exciton binding energy as a function of the band gap and the diamagnetic coefficient. Using an in-plane magnetic field, the exciton fine structure for various 2D perovskites is examined to measure the energy splitting between the excitonic levels. The exciton fine structure and exchange interaction are correlated with structural parameters, employing an effective mass model, to highlight the role of steric effect on the exchange interaction. These findings reveal that lattice distortions, introduced by organic spacers, significantly influence the exchange interaction, driving a tunable energy spacing between dark and bright excitons. This unique feature of 2D perovskites, not present in other semiconductors, offers a novel tuning mechanism for exciton control, making these materials highly promising for efficient light emitters and advanced quantum technologies.
Advanced Energy Materials 15, 9 (2025)205. J. K. König, J. M. Fitzgerald, E. Malic "Magneto-Optics of Anisotropic Exciton Polaritons in Two-Dimensional Perovskites", accepted by Nano Letters (2025)
Layered 2D organic-inorganic perovskite semiconductors support strongly confined excitons that offer significant potential for ultrathin polaritonic devices due to their tunability and huge oscillator strength. The application of a magnetic field has proven to be an invaluable tool for investigating the exciton fine structure observed in these materials. Yet, the combination of an in-plane magnetic field and the strong coupling regime has remained largely unexplored. In this work, we combine microscopic theory with a rigorous solution of Maxwell's equations to model the magneto-optics of exciton polaritons in 2D perovskites. We predict that the brightened dark exciton state can enter the strong coupling regime. Furthermore, the magnetic-field-induced mixing of polarization selection rules and the breaking of in-plane symmetry lead to highly anisotropic polariton branches. This study contributes to a better understanding of the exciton fine structure in 2D perovskites and demonstrates the cavity control of highly anisotropic and polarization-sensitive exciton polaritons.
accepted by Nano Letters204. B. Han, J. M. Fitzgerald, L. Lackner, R. Rosati, M. Esmann, F. Eilenberger, T. Taniguchi, K. Watanabe, M. Syperek, E. Malic, C. Schneider "Infrared magneto-polaritons in MoTe2 mono- and bilayers", Phys. Rev. Letters 134, 076902, selected as Editor's suggestion (2025)
MoTe2 monolayers and bilayers are unique within the family of van-der-Waals materials since they pave the way towards atomically thin infrared light-matter quantum interfaces, potentially reaching the important telecommunication windows. Here, we report emergent exciton-polaritons based on MoTe2 monolayer and bilayer in a low-temperature open micro-cavity in a joint experiment-theory study. Our experiments clearly evidence both the enhanced oscillator strength and enhanced luminescence of MoTe2 bilayers, signified by a 38 % increase of the Rabi-splitting and a strongly enhanced relaxation of polaritons to low-energy states. The latter is distinct from polaritons in MoTe2 monolayers, which feature a bottleneck-like relaxation inhibition. Both the polaritonic spin-valley locking in monolayers and the spin-layer locking in bilayers are revealed via the Zeeman effect, which we map and control via the light-matter composition of our polaritonic resonances.
Phys. Rev. Letters 134, 076902203. R. Rosati, I. Paradisanos, E. Malic, and B. Urbaszek, "Two dimensional semiconductors: Optical and electronic properties", book chapter in "Comprehensive Semiconductor Science and Technology", Second Edition, vol. 1, pp. 312–351, Elsevier
In the last decade atomically thin 2D materials have emerged as a perfect platform for studying and tuning light-matter interaction and electronic properties in nanostructures. The optoelectronic properties in layered materials such as transition-metal-dichalcogenides (TMDs) are governed by excitons, Coulomb bound electron-hole pairs, even at room temperature. The energy, wave function extension, spin and valley properties of optically excited conduction electrons and valence holes are controllable via multiple experimentally accessible knobs, such as lattice strain, varying atomic registries, dielectric engineering as well as electric and magnetic fields. This results in a multitude of fascinating physical phenomena in optics and transport linked to excitons with very specific properties, such as bright and dark excitons, interlayer and charge transfer excitons as well as hybrid and moiré excitons. In this book chapter we introduce general optoelectronic properties of 2D materials and energy landscapes in TMD monolayers as well as their vertical and lateral heterostructures, including twisted TMD hetero- and homobilayer bilayers with moire excitons and lattice recombination effects. We review the recently gained insights and open questions on exciton diffusion, strain- and field-induced exciton drift. We discuss intriguing non-linear many-particle effects, such as exciton halo formation, negative and anomalous diffusion, the surprising anti-funneling of dark excitons.
Comprehensive Semiconductor Science and Technology202. P. G Steeneken, M. Soikkeli, S. Arpiainen, A. Rantala, R. Jaaniso, R. Pezone, S. Vollebregt, S. Lukas, S. Kataria, M. Houmes, R. Álvarez-Diduk, K. Lee, H. Suryo Wasisto, S. Anzinger, M. Fueldner, G. J. Verbiest, F. Alijani, D. Hoon Shin, E. Malic, R. van Rijn, T. Nevanen, A. Centeno, A. Zurutuza, H. S. J. van der Zant, A. Merkoci, G. S. Duesberg and M. Lemme "Towards wafer-scale 2D material sensors", 2D Materials, 12, 2 (2025)
The unique properties of two-dimensional (2D) materials bring great promise to improve sensor performance and realise novel sensing principles. However, to enable their high-volume production, wafer-scale processes that allow integration with electronic readout circuits need to be developed. In this perspective, we review recent progress in on-chip 2D material sensors, and compare their performance to the state-of-the-art, with a focus on results achieved in the Graphene Flagship programme. We discuss transfer-based and transfer-free production flows and routes for complementary metal-oxide-semiconductor (CMOS) integration and prototype development. Finally, we give an outlook on the future of 2D material sensors, and sketch a roadmap towards realising their industrial and societal impact.
2D Materials 12, 2 (2025)