Xiang Dongmei, Li Yulu, Wang Lifeng, Ding Tao, Wang Junhui, Wu Kaifeng
State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China.
University of the Chinese Academy of Sciences, Beijing 100049, China.
J Phys Chem Lett. 2021 Jan 14;12(1):86-93. doi: 10.1021/acs.jpclett.0c03257. Epub 2020 Dec 11.
Solution-processed quantum-confined nanocrystals are important building blocks for scalable implementation of quantum information science. Extensive studies on colloidal quantum dots (QDs) have revealed subpicosecond hole spin relaxation, whereas the electron spin dynamics remains difficult to probe. Here we study electron and hole spin dynamics in CdSe colloidal nanoplatelets (also called quantum wells) of varying thicknesses using circularly polarized transient absorption spectroscopy at room temperature. The clear spectroscopic features of transition bands associated with heavy, light, and spin-orbit split-off holes enabled separate probes of electron and hole dynamics. The hole spin-flip occurred within ∼200 fs, arising from strong spin-orbit coupling in the valence band. The electron spin lifetime decreased from 6.2 to 2.2 ps as the platelet thickness is reduced from 6 to 4 monolayers, reflecting an exchange interaction between the electron and the hole and/or surface dangling bond spins enhanced by quantum confinement.
溶液法制备的量子限域纳米晶体是实现量子信息科学规模化应用的重要基石。对胶体量子点（QDs）的广泛研究揭示了亚皮秒级的空穴自旋弛豫，而电子自旋动力学仍难以探测。在此，我们利用室温下的圆偏振瞬态吸收光谱研究了不同厚度的CdSe胶体纳米片（也称为量子阱）中的电子和空穴自旋动力学。与重空穴、轻空穴和自旋轨道分裂空穴相关的跃迁带具有清晰的光谱特征，从而能够分别探测电子和空穴动力学。空穴自旋翻转发生在约200飞秒内，这是由价带中强烈的自旋轨道耦合引起的。随着纳米片厚度从6个单层减少到4个单层，电子自旋寿命从6.2皮秒降至2.2皮秒，这反映了电子与空穴和/或因量子限域而增强的表面悬挂键自旋之间的交换相互作用。
