Spin Properties in II-VI and Perovskites Colloidal Quantum Dots

Colloidal semiconductor quantum dots (CQDs) have been at the forefront of scientific research for more than two decades, based on their size tunable properties. Although implementation of CQDs in opto-electronic devices already occurs, recent years showed an interest in the investigation of magneto-optical properties of various CQDs with substantial importance for spin-based devices. The talk at NanoIsrael meeting will include the study of two different CQD platforms with unique spin properties.

CdTe/CdSe and Mn⁺²@CdTe/CdSe CQDs: CdTe/CdSe colloidal quantum dots with a soft boundary (alloying), possess quasi type-II configuration (viz., electron and hole are partially separate) and show blinking-free behavior. The Mn⁺² doping induces internal spin interactions between photo-generated species (electron and hole) and the dopant spins, leading to giant magnetization and consequence emission from host-dopant hybrid. The current study developed a method to position the Mn ions selectively either at the core or at the shell. The magneto-optical measurements, including the use of optically detected magnetic resonance, exhibited resonance transitions related to the coupling of the Mn spins with the individual photo-generated carriers.

APbBr₃ (A=Cs⁺, methylamonium): Perovskites semiconductors possess high absorption coefficients as well as long-range transport properties. Currently, they are also prepared in the form of CQDs with very interesting properties including ferroelectricity, magnetism and exciton effects. The magneto-optical measurements of excitons in APbBr₃ as individuals were investigated by monitoring the micro-photoluminescence spectra in the presence of an external magnetic field, while monitoring either the circular or linear polarization components. Gradual band splitting occurring upon the application of a magnetic field, deviating from a common Zeeman interaction behavior, proposes the existence of a more complex mechanism. Theoretical considerations strongly supported the existence of Rashba split in the studied materials, emanated from structural polarization and distortion, viz., breaking of an inversion of symmetry.