Millisecond Spin Relaxation Times of Distinct Electron and Hole Subensembles in MA_xFA_1-xPbI₃ Perovskite Crystals

The unique combination of outstanding optical quality and attractive spin properties opens new avenues for optical spin control in hybrid organic-inorganic perovskite semiconductors. Using the optically detected magnetic resonance technique, we study the spins of electrons and holes in mixed-cation ${\mathrm{MA}}_x{\mathrm{FA}}_{1-x}{\mathrm{PbI}}_3$ single crystals with $x=0.4$ and 0.8. Multiple distinct spin subensembles with absolute values of $g$ -factor spanning from 2.9 to 3.5 for electrons and from 0.5 to 1.6 for holes are resolved, revealing diverse localization environments. We measure the longitudinal spin relaxation times, $T_1$ , reaching 2 ms and remaining in the $\mu s$ range even for weakly localized carriers at cryogenic temperatures. The magnetic-field dependence of $T_1$ is dominated by the random nuclear (Overhauser) fields with strengths of $\sim 0.5$  mT for electrons and $\sim 5-12$  mT for holes. The corresponding correlation times of the hyperfine field are determined by carrier hopping between shallow localization sites. The temperature dependence of $T_1$ reveals a weak localization potential of the charge carriers and shows a correlation between $T_1$ and the inhomogeneity of the spin ensemble. These results establish mixed-A-site perovskite single crystals as a promising solid-state platform with long-lived spin states for quantum information applications.