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

Correlating the magnetic behavior of low dimensional semiconductors with the chemistry used to form these excitonic materials remains crucial to the development of devices applied to quantum information technologies, such as single photon emitters. In this study we use magneto-optical spectroscopy to assess the magnetic response of excitons in defective, hybrid organic-inorganic perovskite-like (HOIP) materials self-assembled into quantum well (SAQW) superlattices. Samples were grown at liquid-liquid interfaces to form specific vacancy defect densities. By applying large magnetic fields in Faraday configurations during the collection of photoluminescence (PL) at 10 K, we assess the magnetic properties of excitons in hexyl ammonium lead iodide (HA2PbI4) SAQWs as a function of their I− vacancy content. For samples shown to possess fewer I− vacancies, the PL spectra are consistent with high quality 1 surfaces like those prepared by encapsulation with 2-dimensional (2D) insulators. These high- quality surfaces allow us to measure sharp doublets of PL peaks possessing full-width-at- half-maximum values as low as 0.65 meV. The sharp, narrow doublets of PL peaks merge into broader individual peaks when we make the same measurements on HA2PbI4 SAQW samples grown to possess more I− vacancies, which is consistent with the presence of a more strongly fluctuating electromagnetic environment. We use the response of the PL spectra of both pristine and defective HA2PbI4 SAQW samples to changes in light field polarization states and applied magnetic field to assign specific PL features to the mJ = 0 manifold of 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 larger exchange interactions and couplings to the applied magnetic field. We support our conclusions with the results of density functional theory calculations on supercells of the proposed defective HA2PbI4 SAQW structure. These results highlight the crucial role chemical conditions can play in the magnetic response of 2D semiconductors towards their application in quantum information technologies.