Seminarium Fizyki Ciała Stałego

Scientific curiosity to uncover original optical properties and functionalities of atomically thin semiconductors, stemming from unusual Coulomb interactions in the two-dimensional geometry and multi-valley band structure, drives the research on monolayers of transition metal dichalcogenides (TMDs). We here infer unusual coherent dynamics of exciton complexes in TMDs occurring on subpicosecond time scale. The dynamics is largely affected by the disorder landscape on the submicron scale, thus can be uncovered using four-wave mixing in the frequency domain, which enables microscopic investigations and imagingWe observe that exciton coherence is lost primarily due to interaction with phonons and relaxation processes towards optically dark excitonic states. Notably, when temperature is low and disorder weak excitons large coherence volume results in huge oscillator strength, allowing to reach the regime of radiatively limited dephasing. We also observe long valley coherence. We thus elucidate the crucial role of exciton environment in the TMDs on its dynamics. By comparing various TMDs materials we show that revealed mechanisms are ubiquitous within that family. 1. T. Jakubczyk, Goutham Nayak, Lorenzo Scarpelli, Wei-Lai Liu, Sudipta Dubey, Nedjma Bendiab, Laëtitia Marty, Takashi Taniguchi, Kenji Watanabe, Francesco Masia, Gilles Nogues, Johann Coraux, Wolfgang Langbein, Julien Renard, Vincent Bouchiat, and Jacek Kasprzak "Coherence and Density Dynamics of Excitons in a Single-Layer MoS2 Reaching the Homogeneous Limit" ACS Nano 2019 13 (3)2. T. Jakubczyk, K. Nogajewski , M. Molas , M. Bartos , W. Langbein , M. Potemski and J. Kasprzak, "Impact of environment on dynamics of exciton complexes in a WS2 monolayer" T. Jakubczyk, K. Nogajewski , M. Molas , M. Bartos , W. Langbein , M. Potemski and J. Kasprzak 2D Mater. 5 (2018) 3. T. Jakubczyk, V. Delmonte, M. Koperski, K. Nogajewski, C. Faugeras, W. Langbein, M. Potemski, and J. Kasprzak, "Radiatively Limited Dephasing and Exciton Dynamics in MoSe2 Monolayers Revealed with Four-Wave Mixing Microscopy," Nano Lett 16 (9) (2016). UwagaSeminarium w trybie zdalnympatrz instrukcja :instrukcja: (pdf file)AttentionThe seminar in the remote modesee instruction :instruction: (pdf file)