Demystifying and Controlling the Exciton Fine Structure in Single Inorganic Perovskite Nanoplatelets

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The high versatility of lead halide perovskite nanocrystals opened enormous prospects for classical light emitting devices as well as for quantum emitters that are highly required, e.g., for quantum information technology. The latter requires a detailed understanding of the exciton transitions in individual nanocrystals and their control by tailoring the nanocrystals and by applying well-defined external fields. Hitherto, the random orientation of individual nanocrystals in single particle experiments inhibits the assignment of the individual components of the exciton fine structure to the respective crystal axes. Moreover, magnetic as well as electrical fields have already been applied to externally control the emission pattern of individual lead halide perovskite nanocrystals. However, the lack of control of the single nanocrystal orientation with respect to the field directions hampers the determination of the g-factor and the induced and permanent electrical dipoles with respect to the crystal axes until now. The objective of this proposal is the investigation of the exciton fine structure in single anisotropic size engineered CsPbBr3 nanoplatelets and its manipulation by directional electric and magnetic fields that are well-defined with respect to the crystal axes. This novel idea makes use of our recent discovery that the distinct shape anisotropy and high stability of the nanoplatelets allow deposition of single nanoplatelets with a clearly defined (flat) alignment on a pre-patterned substrate and enable determination of their absolute orientation by emission polarisation measurements. Applying magnetic as well as electrical fields to single nanoplatelets, we will derive the anisotropy of the g-factor as well as the permanent electrical dipole moments and the electrical polarizability with respect to the crystal axes. We envision to elaborate the potential of applied electric fields along specific crystal axes to control and finally eliminate the fine structure splitting on the route towards entangled photon sources based on single lead halide perovskite nanocrystals.