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

卤化铅钙钛矿纳米晶的多功能性为经典发光器件以及量子信息技术等高要求的量子发射器开辟了广阔的前景。后者需要详细了解单个纳米晶体中的激子跃迁，并通过剪裁纳米晶体和施加明确定义的外场来控制它们。到目前为止，单个纳米晶体在单粒子实验中的随机取向阻碍了激子精细结构的各个分量被分配到各自的晶轴。此外，磁场和电场已经被用来外部控制单个卤化铅钙钛矿纳米晶的发射模式。然而，缺乏对单个纳米晶体取向对场方向的控制，阻碍了g因子的确定以及诱导和永久电偶极子相对于晶轴的确定。该方案的目的是研究单个各向异性尺寸的工程化CsPbBr3纳米片中的激子精细结构以及关于晶轴的定向电场和磁场对激子精细结构的控制。这一新的想法利用了我们最近的发现，即纳米小片独特的形状各向异性和高稳定性允许在预图案化的衬底上沉积具有明确定义(平坦)排列的单个纳米小片，并能够通过发射偏振测量来确定其绝对取向。在单个纳米片上施加磁场和电场，我们将得到g因子的各向异性，以及永久电偶极矩和关于晶轴的电极化率。我们设想沿着特定的晶轴施加电场来控制并最终消除基于单个卤化铅钙钛矿纳米晶的纠缠光子源的精细结构分裂。

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.