Modified Exciton Exchange Coupling and Magnetic Interactions in Defective 2D Hybrid Lead Iodide Perovskites

Excitonic low-dimensional semiconductors play a crucial role in the evolution of quantum information technologies, such as single-photon emitters. Because of that opportunity, correlating the magnetic behavior of these 2D materials with the chemistry used to form them remains crucial. This work uses magneto-optical spectroscopy to assess the magnetic response of excitons in defective, hybrid organic-inorganic [hexyl ammonium lead iodide (HA₂PbI₄)] self-assembled quantum well (SAQW) superlattices grown at liquid-liquid interfaces to form specific vacancy defects. Pristine (fewer I^- vacancies) and more defective samples were grown and compared via perform magneto-photoluminescence (PL) measurements in Faraday configuration with magnetic fields up to 9 T at 10 K. The results determine the magnetic properties of excitons as a function of their I− vacancy content. The PL spectra of the pristine samples are consistent with high-quality surfaces compared with those prepared by encapsulation with 2D insulators. [1] The PL spectra of less defective samples show sharp doublets of peaks whose line widths, approximately 0.65 meV. On the other hand, for the more defective samples that possess more I- vacancies, the sharp and narrow doublets of PL peaks merge into a broader single peak. This broadening is expected to result from a more strongly fluctuating electromagnetic environment caused by the vacancies. We study the relative light field polarization states and effects of applied magnetic field on the PL spectra of each type of sample to assign specific features to m_J = 0 manifold of the excitons that are coupled via the exchange interaction. Additionally, we assign lower energy features in these samples’ PL spectra to excitons trapped at defect sites, which possess stronger exchange interactions and couplings to the applied magnetic fields. We support our conclusions with the results of density functional theory (DFT) calculations on supercells of the proposal defective HA₂PbI₄ SAQW. These results highlight the crucial role chemical conditions of materials synthesis can play in the light emission spectra and magnetic response of low-dimensional semiconductors.