Coherent Electron Spin Precession Enabled by Ultrafast Hole Transfer in Type-II Two-Dimensional Perovskites

Two-dimensional (2D) lead halide perovskites constitute a versatile platform to explore the intriguing interplay between electron spin, light helicity, and structural chirality for novel quantum and spintronic applications. However, strong electron-hole exchange interaction limits the spin lifetime in typical 2D monolayer perovskites to be as short as subps. While recent studies employed organic spacer engineering to extend the spin lifetime to above 10 ps at room temperature, coherent spin precession, which is a starting point to exploit the genuine quantum nature of the optically injected spins, has not been realized in these systems. Here, we study spin relaxation and precession dynamics in a type-II 2D perovskite with carbazole-based organic spacers. Ultrafast hole transfer (ca. 60 fs) from the inorganic layer to the organic layer decouples electron-hole interaction, giving rise to a room-temperature electron spin lifetime of 40 ps that is 200-fold longer than typical 2D perovskites. The spin lifetime is further prolonged to 260 ps at 60 K, with the temperature dependence well described by scattering with phonon modes of ca. 22 meV. Most importantly, coherent electron spin precession under a transverse magnetic field is directly observed. Dephasing time is also limited by phonon scattering, but the phonon modes of ca. 11 meV are distinct from those responsible for spin depolarization. This work not only provides key mechanistic insights into spin relaxation and precession dynamics in 2D perovskites but also establishes the viability of these materials as a novel platform for spin quantum manipulation.