Martin Wood Complex, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU
Dr Aurelie Champagne, Institut de Chimie de la Matière Condensée de Bordeaux
Prof. Marina Filip
Abstract
Interfacing transition metal dichalcogenides (TMDs) into van der Waals heterostructure bilayers with type-II level alignment has led to recent reports of interlayer excitons with large binding energies, long lifetimes, and signatures of exciton condensation at elevated temperatures. Atomically flat two-dimensional molecular crystals (MC) on TMD monolayers is an emerging interfacial quantum materials platform with tunable level alignment, exciton binding energies, and photoluminescence, given the heightened sensitivity of the organic layers to their environment. In addition to non-local adsorbate/substrate screening, free charge carrier screening is particularly relevant in MC-TMD bilayer heterostructures, and controllably altering these distinct modes of screening can lead to new phenomena. Using a dielectric embedding ab initio GW plus Bethe-Salpeter equation (GW-BSE) approach [1], we compute energy level alignment as well as neutral excitations at MC-TMD interfaces (MC = PDI or PTCDA ; TMD = MoS2 or WS2), exploring new emergent optical transitions, such as those associated with interlayer excitons characterized by electrons and holes separated between the MC adsorbate and the TMD, respectively [2-3]. Using an extended plasmon-pole model reducing computational cost with no loss of accuracy [4-5] and explicit addition of electrons, we also explore the role of free charge carriers in screening electron-hole interactions, quasiparticle energy level alignment, and the nature of interlayer excitons.
[1] Z. Liu, F. H. da Jornada, S. G. Louie, J. B. Neaton, J. Chem. Theory Comput. 15 (2019) 4218-4227.
[2] T. Chowdhury, A. Champagne*, F. Mujid, P. Knüppel, C. Liang, A. Ray, M. Gao, M. Lee, D. A. Muller, N. Guisinger, K. F. Mak, J. B. Neaton, J. Park, Submitted (2024).
[3] A. Champagne, A. Adeniran, J. B. Haber, Z. Liu, J. B. Neaton, In preparation.
[4] A. Champagne, J. B. Haber, S. Pokawanvit, D. Y. Qiu, S. Biswas, H. A. Atwater, F. H. da Jornada, J. B. Neaton, Nano Lett. 10, 23 (2023) 4274-4281.
[5] S. Biswas, A. Champagne*, J. B. Haber, S. Pokawanvit, J. Wong, H. Akbari, S. Krylyuk, K. Watanabe, T. Taniguchi, A. V. Davydov, Z. Y. Al Balushi, D. Y. Qiu, F. H. da Jornada, J. B. Neaton, H. A. Atwater, ACS Nano 8, 17 (2023) 7685-7694.
Dr. Aurelie Champagne is a permanent researcher at the Institute of Chemistry and Condensed Matter of Bordeaux (ICMCB). She received her Ph.D. in Science Engineering and Technology in 2020 from the Institute of Condensed Matter and Nanosciences at UCLouvain (Belgium), where she studied the physical properties of a novel family of two-dimensional materials, MXenes, using a combination of experiments and ab initio calculations. From 2021 to 2024, she was a postdoctoral researcher in the group of Jeffrey B. Neaton at the Lawrence Berkeley National Laboratory (USA). During her postdoctoral research, she developed and applied theoretical models to predict the electronic, optical, and transport properties of low-dimensional materials, with foreseen applications in optoelectronic and energy-related devices. Dr. Champagne’s current research interests include modeling and understanding ionic transport mechanisms in solid-state electrolytes and their interfaces with electrode materials.