Exciton Fine Structure in Lead Chalcogenide Quantum Dots: Valley Mixing and Crucial Role of Intervalley Electron−Hole Exchange

We study the exciton fine structure in quantum dots of multi-valley lead chalcogenides [1]. We demonstrate that inter-valley electron-hole exchange interaction, ignored in previous studies, dramatically modifies the exciton fine structure and leads to appearance of the ultra-bright valley-symmetric spin-triplet exciton state dominating inter-band optical absorption. Valley mixing leads to brightening of other symmetry-allowed spin-triplet states which dominate low-temperature photoluminescence. Our results are in agreement with recent experiments on optical spectroscopy of individual PbS/CdS core/shell quantum dots yielding temperature dependences of photoluminescence line-shapes [2].

[1] I.D. Avdeev, M.O. Nestoklon, and S.V. Goupalov, Nano Lett., https://dx.doi.org/10.1021/acs.nanolett.0c03937
[2] Z. Hu, Y. Kim, S. Krishnamurthy, I.D. Avdeev, M.O. Nestoklon, A. Singh, A.V. Malko, S.V. Goupalov, J.A. Hollingsworth, and H. Htoon, Nano Lett. 19, 8519 (2019).