Genco Armando, Trovatello Chiara, Shahnazaryan Vanik A, Dogadov Oleg, Cadore Alisson R, Rosa Barbara L T, Kerfoot James A, Ahmed Tanweer, Balci Osman, Alexeev Evgeny M, Rostami Habib, Watanabe Kenji, Taniguchi Takashi, Tongay Seth Ariel, Ferrari Andrea C, Cerullo Giulio, Dal Conte Stefano
Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, Milano, 20133, MI, Italy.
Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States.
Nano Lett. 2025 May 14;25(19):7673-7681. doi: 10.1021/acs.nanolett.4c06428. Epub 2025 Apr 30.
Quantum confinement and reduced dielectric screening lead to strong excitonic effects in atomically thin transition metal dichalcogenides (TMDs). Encapsulation of TMD monolayers in hexagonal boron nitride (hBN) unveils the excitonic Rydberg series below the free particle bandgap. The nonequilibrium response and the dynamics of these higher order exciton states and their multiparticle complexes remain almost unexplored. Here we use ultrafast pump-probe optical microscopy to measure the dynamics of excited-state (2s) excitons in hBN-encapsulated monolayer WSe. 2s excitons form through an ultrafast relaxation process from high-energy states and exhibit longer decay dynamics than ground state excitons due to their higher spatial extension. We detect light-induced formation of 2s trions with significant oscillator strength and faster decay dynamics than 2s excitons, attributed to an intra-excitonic Auger effect causing an additional decay channel. Our results shed light on the dynamics of excited state excitons in TMDs and their interactions with free carriers.
量子限制和降低的介电屏蔽导致原子级薄的过渡金属二硫属化物（TMD）中出现强激子效应。将TMD单层封装在六方氮化硼（hBN）中，揭示了自由粒子带隙以下的激子里德堡系列。这些高阶激子态及其多粒子复合物的非平衡响应和动力学几乎仍未得到探索。在这里，我们使用超快泵浦-探测光学显微镜来测量hBN封装的单层WSe中激发态（2s）激子的动力学。2s激子通过从高能态的超快弛豫过程形成，并且由于其更大的空间扩展，表现出比基态激子更长的衰减动力学。我们检测到具有显著振子强度且衰减动力学比2s激子更快的光致2s三激子的形成，这归因于激子内俄歇效应导致的额外衰减通道。我们的结果揭示了TMD中激发态激子的动力学及其与自由载流子的相互作用。
