Main Content
Publications 2026
224. B. Kirubasankar, A. Mondal, S. Joon Yun, D. Daw, Y. Xu, L.-A. T. Nguyen, Y. Koo, K. Kumar Paul, H. Hong, H. Lee, Y. Luo, K. Liu, N. Higashitarumizu, D. Erkensten, C. Yun Heo, Y.-R. Jeon, T. Lee, D.-H. Nam, X. Liu, S. M. Kim, D. L. Duong, Q. Wu, D. Akinwande, M. C. Hersam, A. Javey, E. Malic, B. Liu, T. Zhai, H. Yang, K.-D. Park, K. K. Kim, and Y. H. Lee, "Contemporary Challenges in van der Waals 2D Semiconductors", ACS Nano 20, 3228 (2026)
Van der Waals (vdW) layered semiconductors have emerged as a unique class of quantum materials distinguished from their bulk counterparts by reduced dielectric screening, strong Coulomb interactions, large exciton binding energies, strong spin− orbit coupling, and pronounced thickness-dependent band structures. These fundamental attributes have enabled the exploration of exotic many-body physics and a broad spectrum of device applications, ranging from field-effect transistors and ferroelectric switches to optoelectronics, magnetic semiconductors, neuromorphic computing, and energy harvesting systems. Despite remarkable advances, critical challenges remain in the controlled synthesis of high-quality crystals, formation of low-resistance contacts, integration of stable and scalable gate dielectrics, and reliable device performance at the wafer scale. In this mega-review, we provide a comprehensive overview of contemporary challenges and future opportunities in vdW-layered semiconductors, structured across nine themes: growth and heterostructures of transition metal dichalcogenides, Ohmic contacts, emerging gate dielectrics, high-performance low-power field-effect transistors (FETs), diluted magnetic semiconductors, plasmonics and exciton propagation, hot-carrier solar cells, bioinspired neuromorphic computing, and electrocatalytic/photocatalytic energy conversion. By consolidating fundamental insights and device-level perspectives, this review aims to chart a roadmap for advancing vdW semiconductors from laboratory-scale discoveries to transformative technologies in electronics, optoelectronics, spintronics, and sustainable energy systems.
ACS Nano 20, 3228 (2026)223. D. Erkensten, A. Chernikov, E. Malic, "Impact of an electron Wigner crystal on exciton propagation", accepted by Nano Letters (2026)
The strong Coulomb interaction in 2D materials facilitates the formation of tightly bound excitons and charge-ordered phases of matter. A prominent example is the formation of a crystalline phase from free charges due to mutual Coulomb repulsion, known as the Wigner crystal. While exciton- electron interactions have been used as a sensor for Wigner crystallization, its impact on exciton properties has been poorly understood so far. Here, we show that the weak potential induced by periodically ordered Wigner crystal electrons has a major impact on exciton propagation, albeit having only a minor influence on exciton energy. The effect is tunable with carrier density determining the Wigner crystal confinement and temperature via thermal occupation of higher subbands. Our work provides microscopic insights into the interplay between excitons and charge-ordered states identifying key signatures in exciton transport, and establishes a theoretical framework for understanding exciton propagation in the presence of strong electronic correlations.
accepted by Nano Letters (2026)222. P. Werner, W. Bennecke, J. P. Bange, G. Meneghini, D. Schmitt, M. Merboldt, A. M. Seiler, A. AlMutairi, K. Watanabe, T. Taniguchi, G. S. Matthijs Jansen, J. Liu, D. Steil, S. Hofmann, R. Thomas Weitz, E. Malic, S. Mathias, M. Reutzel "The role of non-equilibrium populations in dark exciton formation", accepted by Physical Review Letters (2026)
In two-dimensional transition metal dichalcogenide structures, the optical excitation of a bright exciton may be followed by the formation of a plethora of lower energy dark states. In these formation and relaxation processes between different exciton species, non-equilibrium exciton and phonon populations play a dominant role, but remain so far largely unexplored as most states are inaccessible by regular spectroscopies. Here, on the example of homobilayer 2H-MoS, we realize direct access to the full exciton relaxation cascade from experiment and theory. By measuring the energy- and in-plane momentum-resolved photoemission spectral function, we reveal a distinct fingerprint for dark excitons in a non-equilibrium excitonic occupation distribution. In excellent agreement with microscopic many-particle calculations, we quantify the timescales for the formation of a non-equilibrium dark excitonic occupation and its subsequent thermalization to 85~fs and 150~fs, respectively. Our results provide a previously inaccessible view of the complete exciton relaxation cascade, which is of paramount importance for the future characterization of non-equilibrium excitonic phases and the efficient design of optoelectronic devices based on two-dimensional materials.
accepted by Physical Review Letters (2026)