Band-edge Exciton Fine Structure in Lead-halide Perovskite Nanocrystals
Philippe Tamarat a
a LP2N, Univ. Bordeaux, IOGS &CNRS, Talence (France)
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#PERFuDe19. Halide perovskites: when theory meets experiment from fundamentals to devices
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Claudine Katan, Wolfgang Tress and Simone Meloni
Oral, Philippe Tamarat, presentation 306
Publication date: 16th July 2019

The ability to tailor the band-edge exciton fine structure is of prime importance for the realization of efficient single-photon sources or sources of entangled photons for quantum information processes. Yet, in lead halide perovskites, the physics of the fine structure is not elucidated. The band-edge exciton is formed by the Coulomb interaction between a hole in an S-like state Jh=1/2, and an electron in a spin−orbit split-off state (Je=1/2), so that the fine structure comprises a dark singlet state (J=0) and a bright triplet manifold (J=1). Recent investigations of single inorganic perovskite nanocrystals at liquid helium temperatures have revealed that the bright triplet sublevels display an intense photoluminescence and energy splittings lying in the meV range[1-3]. Since no direct signature of the dark state has been provided so far, a controversy has developed concerning the physical mechanisms at the origin of these observations.

 We use low-temperature magneto-optical spectroscopy of FAPbBr3 single nanocrystals to identify their entire band-edge exciton fine structure. In particular, magnetic brightening of the dark singlet exciton shows evidence for a dark singlet state being located ~2.5 meV below the bright triplet[4]. These results are at variance with the recent statement that due to a Rashba effect, perovskite nanocrystals are the only known exception to the rule of a dark ground exciton state among all bulk semiconductors and all existing semiconductor heterostructures[3,5]. The observed bright-dark splitting is interpreted as the result of the long-range electron-hole exchange interaction. We also show that the strong photoluminescence is not hindered by the lowest dark state because of a reduced bright-to-dark spin relaxation rate in these systems, making them suitable for the development of quantum light sources.


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