Kontolle der elektronischen und optischen Eigenschaften von Heterostrukturen zweidimensionaler Kristalle

• Antragsteller: Professor Dr. Tobias Korn; Professor Dr. Gotthard Seifert
• Fachliche Zuordnung: Experimentelle Physik der kondensierten Materie ; Theoretische Physik der kondensierten Materie
• Förderung: Förderung von 2016 bis 2022
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 317551441

Zusammenfassung der Projektergebnisse

The aim of our project was the study of van der Waals (vdW) heterostructures (HS) consisting of different two-dimensional crystals, with a focus on the semiconducting transition metal dichalcogenides (TMDCs). On the experimental side, we improved the techniques of deterministic transfer of 2D materials, allowing us to fabricate HS with well-defined interlayer twist angle, strong interlayer coupling and excellent optical properties. We performed many spectroscopic studies, employing mostly photoluminescence and Raman spectroscopy. On the theory side, we utilized first-principles calculations to determine the electronic and optical properties of various vdW HS and optimized methods for dealing with the unique challenges of these structures, such as the large supercells arising from crystallographic misalignment. Our joint goal was to understand, and ultimately control the electronic and optical properties of vdW HS. The prime example highlighting our achievements towards this goal is our joint work on Momentum-space indirect interlayer excitons in MoS2/WSe2 van der Waals heterostructures (J. Kunstmann et al., Nature Physics, 2018), where we combined all the experimental and calculation tools described above. Here, we were able to show that the interlayer exciton emission in this material combination first observed by Fang et al. actually stems from momentumindirect interlayer excitons, and that holes at the Γ point are delocalized over the two constituent layers. This work represents a crucial step towards the understanding and control of excitonic effects in TMDC heterostructures and devices and has already been cited well over 100 times (Web of Science). It has also generated a lot of online media attention, being featured by more than 70 media outlets (according to Altmetric). Further important contributions were made regarding magneto-spectroscopy of 2D crystals and vdW heterostructures by the PIs working together with international collaboration partners such as Tomasz Wozniak (Wroclaw), Andrey Chaves (Fortaleza) and Misha Glazov (St. Petersburg). On the theory side, for example, g factors for interlayer exciton transitions could be calculated. On the experimental side, the momentum-space arrangement of the constituent quasiparticles in biexcitons could be revealed by magneto-spectroscopy. We also elucidated phenomena related to moiré effects and atomic reconstruction in vdW heterostructures, which influence the diffusion of interlayer excitons and modify the Raman spectrum. To summarize, our joint project has helped to advance the field of van der Waals heterostructures, which is still vibrant, as evidenced by the recent establishment of a focus program called ‘2D Materials – Physics of van der Waals [hetero]structures’ by the DFG.

Projektbezogene Publikationen (Auswahl)

• Momentum-space indirect interlayer excitons in MoS2/WSe2 van der Waals heterostructures. Nature Physics 14, 801 (2018)
  J. Kunstmann, F. Mooshammer, P. Nagler, A. Chaves, F. Stein, N. Paradiso, G. Plechinger, C. Strunk, C. Schüller, G. Seifert, D. R. Reichman, T. Korn
  
• Zeeman Splitting and Inverted Polarization of Biexciton Emission in Monolayer WS2, Phys. Rev. Lett. 121, 057402 (2018)
  P. Nagler, M. V. Ballottin, A. A. Mitioglu, M. V. Durnev, T. Taniguchi, K. Watanabe, A. Chernikov, C. Schüller, M. M. Glazov, P. C. M. Christianen, and T. Korn
  
• Interlayer excitons in transition-metal dichalcogenide heterobilayers. physica status solidi (b) 256, 1900308 (2019)
  P. Nagler, F. Mooshammer, J. Kunstmann, M. V. Ballottin, A. Mitioglu, A. Chernikov, A. Chaves, F. Stein, N. Paradiso, S. Meier, G. Plechinger, C. Strunk, R. Huber, G. Seifert, D. R. Reichman, P. C. M. Christianen, C. Schüller, T. Korn
  
• Luminescent emission of excited Rydberg excitons from monolayer WSe2. Nano Letters 19, 2464 (2019)
  S.-Y. Chen, Z. Lu, T. Goldstein, J. Tong, A. Chaves, J. Kunstmann, L. S. R. Cavalcante, T. Woźniak, G. Seifert, D. R. Reichman, T. Taniguchi, K. Watanabe, D. Smirnov, J. Yan
  
• Exciton g factors of van der Waals heterostructures from first-principles calculations, Phys. Rev. B 101, 235408 (2020)
  T. Wozniak, P. E. Faria Junior, G. Seifert, A. Chaves, and J. Kunstmann
  
• Low-frequency Raman scattering in WSe2−MoSe2 heterobilayers: Evidence for atomic reconstruction, Appl. Phys. Lett. 117, 013104 (2020)
  J. Holler, S. Meier, M. Kempf, P. Nagler, K. Watanabe, T. Taniguchi, T. Korn, and C. Schüller
  
• Twist-angle-dependent interlayer exciton diffusion in WS2-WSe2 heterobilayers. Nature Materials 19, 617–623 (2020)
  L. Yuan, B. Zheng, J. Kunstmann, T. Brumme, A. B. Kuc, C. Ma, S. Deng, D. Blach, A. Pan, L. Huang
  
• Large exciton binding energies in MnPS3 as a case study of a van der Waals layered magnet, Phys. Rev. B, 103(12), L121108 (2021)
  M. Birowska, P. E. Faria Junior, J. Fabian, and J. Kunstmann
  
• Moiré phonons in twisted MoSe2–WSe2 heterobilayers and their correlation with interlayer excitons, 2D Mater. 8, 035030 (2021)
  P. Parzefall, J. Holler, M. Scheuck, A. Beer, K.-Q. Lin, B. Peng, B. Monserrat, P. Nagler, M. Kempf, T. Korn, and C. Schüller
  
• Tuning Valleys and Wave Functions of van der Waals Heterostructures by Varying the Number of Layers: A First-Principles Study, Small, 17(23) (2021)
  M. S. Ramzan, J. Kunstmann, A. B. Kuc