厦门大学化学化工学院

报告摘要:

Two-dimensional transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. We present the existence of a new excitonic species, the high-lying exciton (HX), in transition metal dichalcogenide monolayers with almost twice the band-edge A-exciton energy and with a linewidth as narrow as that of band-edge excitons [1]. The HX is populated through momentum-selective optical excitation in the K-valleys, and is identified experimentally in upconverted photoluminescence (UPL) and theoretically in ab initio GW-BSE calculations. These calculations suggest that the HX is comprised of electrons of negative effective mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalize the efficient exciton-exciton annihilation in TMDC monolayers, and enables the excitonic quantum-interference phenomenon revealed in optical second-harmonic generation (SHG) [2]. We probe the excitonic temporal dynamics in such three-level system through time-resolved sum-frequency generation (SFG) and four-wave mixing (FWM) [3]. High-lying excitons in bilayer WSe₂ can be largely tuned by twisting [4], electrical gate [5,6] and Stark effect, which gives control over the excitonic quantum interference and the corresponding optical nonlinearity.

[1] K. -Q. Lin et al., Nat. Commun. 12, 5500 (2021).

[2] K. -Q. Lin et al., Nat. Phys. 15, 242-246 (2019).

[3] J. M. Bauer et al., Nat. Photon. 16, 777-783 (2022).

[4] K. -Q. Lin et al., Nat. Commun. 12, 1553 (2021).

[5] K. -Q. Lin et al., Nat. Commun. 13, 6980 (2022). 

[6] K. -Q. Lin et al., Nat. Nanotechnol. 19, 196 (2024). 

报告人简介:

林楷强，本科毕业于厦门大学化学系（2013），于2018年获得厦门大学物理化学博士学位，师从田中群院士、任斌教授；随后赴德国雷根斯堡大学物理系从事博士后工作，于2020年受聘雷根斯堡大学Akademischen Rat a. Z.教职，期间获德国国家科学基金（DFG）项目（2项）和中德国际交流项目等基金项目的资助；入选国家高层次青年人才，于2023年加入厦门大学化学化工学院，主要从事凝聚态动力学、超快非线性光谱、二维半导体等领域的研究，以第一和通讯作者在Nature Physics、Nature Photonics、Nature Nanotechnology、Nature Communications（4 篇）等杂志发表论文10余篇，获2023年德国物理学会华特·肖特基奖。

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