Origin of Rashba Spin-Orbit Coupling in 2D and 3D Lead Iodide Perovskites

We studied spin dynamics of charge carriers in the superlattice-like Ruddlesden-Popper hybrid lead iodide perovskite semiconductors, 2D (BA)₂(MA)Pb₂I₇ (with MA = CH₃NH₃, and BA = CH₃(CH₂)₃NH₃), and 3D MAPbI₃ using the magnetic field effect (MFE) on conductivity and electroluminescence in their light emitting diodes (LEDs) at cryogenic temperatures. The semiconductors with distinct structural/bulk inversion symmetry breaking, when combined with colossal intrinsic spin-orbit coupling (SOC), theoretically give rise to giant Rashba-type SOC. We found that the magneto-conductance (MC) magnitude increases monotonically with the emission intensity and saturates at ≈0.05% and 0.11% for the MAPbI₃ and (BA)₂(MA)Pb₂I₇, respectively. The magneto-electroluminescence (MEL) response with similar line shapes as the MC response has a significantly larger magnitude, and essentially stays constant at ≈0.22% and ≈0.20% for MAPbI₃ and (BA)₂(MA)Pb₂I₇, respectively. The sign and magnitude of the MC and MEL responses can be quantitatively explained in the framework of the Δg-based excitonic model using rate equations. Remarkably, the width of the MEL response in those materials linearly increases with increasing the applied electric field, where the Rashba coefficient in (BA)₂(MA)Pb₂I₇ is estimated to be about 7 times larger than that in MAPbI₃. Our studies might have significant impact on future development of electrically-controlled spin logic devices via Rashba-like effects.