Fast Diffusion of Spin Polarized Excitons in Organic-Inorganic Lead Halide Perovskites

The hybrid organic-inorganic lead halide perovskites have recently attracted tremendous attention from the condensed matter and nanotechnology communities. This interest arises from their intriguing optoelectronic properties with an emerging potential for light-harvesting and light-emitting applications. We investigate the spin diffusion of the excitons in FA(0.9)Cs(0.1)PbI(2.8)Br(0.2) perovskite crystals at cryogenic temperatures by employing ultrafast temporally and spatially resolved magneto-optical Kerr microscopy. We find a large exciton spin diffusion coefficient on the order of similar to 100 cm(2)/s. The spin polarization signal has a very intricate dependence on the pump power & horbar;beyond a certain pump power threshold, an anomalous, nonlinear spatial and temporal dependence is observed. These experimental findings are modeled within the framework of the kinetic theory and are explained by a memory effect. Specifically, a spatial and temporal temperature variation induced by the pump pulse implies a variation of the exciton spin lifetime.