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Slow Cooling of High‐Energy C Excitons Is Limited by Intervalley‐Transfer in Monolayer MoS 2
Author(s) -
Li Yuanzheng,
Shi Jia,
Chen Heyu,
Mi Yang,
Du Wenna,
Sui Xinyu,
Jiang Chuanxiu,
Liu Weizhen,
Xu Haiyang,
Liu Xinfeng
Publication year - 2019
Publication title -
laser and photonics reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.778
H-Index - 116
eISSN - 1863-8899
pISSN - 1863-8880
DOI - 10.1002/lpor.201800270
Subject(s) - exciton , picosecond , femtosecond , monolayer , ultrafast laser spectroscopy , materials science , spectroscopy , biexciton , ultrashort pulse , femtochemistry , relaxation (psychology) , absorption (acoustics) , molecular physics , optoelectronics , condensed matter physics , atomic physics , physics , optics , nanotechnology , psychology , social psychology , laser , quantum mechanics
High‐energy C exciton in 2D transition metal dichalcogenides with strong photon absorption can be utilized prospectively in light‐harvesting and opto‐electric devices. Here, a detailed study on C exciton dynamics in monolayer MoS 2 is presented by femtosecond transient absorption (TA) spectroscopy. In the experiment, the C exciton with unique parallel band structure exhibits a slow process within tens of picoseconds (≈10–50 ps) as well as a fast process within several picoseconds (≈1–6 ps) instead of previous reported ultrafast cooling (<500 fs) process. From TA spectroscopy, the experimental results confirmed that the relatively slow cooling of C exciton is mainly limited by the rates of intervalley transfer rather than Pauli blocking effect from band‐edge excitons. The timescale of intervalley transfer is longer than that of intraband relaxation of C exciton, therefore, leading to the slow cooling of C exciton. Moreover, intervalley transfer time are estimated with two processes of 5.1 ± 0.6 ps and 69.5 ± 8 ps when the pump fluence is ≈127 µJ cm −2 . This work provides further understanding of the ultrafast dynamics of C exciton in monolayer MoS 2 and opens new opportunities for opto‐electric related applications.