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

卤化铅钙钛矿纳米晶体的高通用性为经典发光器件以及高度要求的量子发射体（例如量子信息技术）开辟了巨大的前景。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应用定义良好的外场来控制它们。迄今为止，在单粒子实验中，单个纳米晶体的随机取向抑制了激子精细结构的单个组分分配到各自的晶体轴上。此外，磁场和电场已经被应用于外部控制单个卤化铅钙钛矿纳米晶体的发射模式。然而，到目前为止，缺乏对单纳米晶体取向相对于场方向的控制阻碍了g因子和相对于晶体轴的感应和永久电偶极子的确定。本研究的目的是研究单各向异性尺寸工程CsPbBr3纳米片的激子精细结构及其在相对于晶体轴明确定义的定向电场和磁场下的操纵。这个新颖的想法利用了我们最近的发现，即纳米片的独特形状各向异性和高稳定性允许在预图板上沉积具有明确定义（平坦）排列的单个纳米片，并能够通过发射偏振测量确定它们的绝对方向。将磁场和电场应用于单个纳米薄片，我们将推导出g因子的各向异性以及相对于晶体轴的永久电偶极矩和电极化率。我们设想详细阐述沿特定晶体轴施加电场的潜力，以控制并最终消除基于单一卤化铅钙钛矿纳米晶体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.