Tuning Spin-Polarized Lifetime at High Carrier Density through Deformation Potential in Dion–Jacobson-Phase Perovskites

The control of spin relaxation mechanisms is of great importance for spintronics applications as well as for fundamental studies. Layered metal-halide perovskites represent an emerging class of semiconductors with rich optical spin physics, showing potential for spintronic applications. However, a major hurdle arises in layered metal-halide perovskites with strong spin–orbit coupling, where the spin lifetime becomes extremely short due to D'yakonov–Perel' scattering and Bir–Aronov–Pikus at high carrier density. Using the circularly polarized pump–probe transient reflection technique, we experimentally reveal the important scattering for spin relaxation beyond the electron–hole exchange strength in the Dion–Jacobson (DJ)-type 2D perovskites (3AMP)(MA)n−1PbnI3n+1 [3AMP = 3-(aminomethyl)piperidinium, n = 1–4]. Despite a more than 10-fold increase in carrier concentration, the spin lifetimes for n = 3 and 4 are effectively maintained. We reveal neutral impurity and polar optical phonon scatterings as significant contributors to the momentum relaxation rate. Furthermore, we show that more octahedral distortions induce a larger deformation potential which is reflected on the acoustic phonon properties. Coherent acoustic phonon analysis indicates that the polaronic effect is crucial in achieving control over the scattering mechanism and ensuring spin lifetime protection, highlighting the potential of DJ-phase perovskites for spintronic applications.