  Photoinduced spin-charge interconversion in semiconductors with spin-orbit
coupling could provide a route to optically addressable spintronics without the
use of external magnetic fields. A central question is whether the resulting
spin-associated charge currents are robust to structural disorder, which is
inherent to polycrystalline semiconductors that are desirable for device
applications. Using femtosecond circular polarization-resolved pump-probe
microscopy on polycrystalline halide perovskite thin films, we observe the
photoinduced ultrafast formation of spin-polarized positive and, unexpectedly,
negative spin domains on the micron scale formed through lateral currents.
Further, the polarization of these domains and lateral transport direction is
switched upon switching the polarization of the pump helicity. Micron scale
variations in the intensity of optical second-harmonic generation and vertical
piezoresponse suggest that the spin domain formation is driven by the presence
of strong local inversion symmetry breaking via inter-grain structural
disorder. We propose that this leads to spatially varying Rashba-like spin
textures that drive spin-momentum locked currents, leading to local spin
accumulation. Our results establish ultrafast spin domain formation in
polycrystalline semiconductors as a new optically addressable platform for
nanoscale spin-device physics.
