Abstract
The outstanding optical quality of lead halide perovskites inspires studies of their potential for the optical control of carrier spins as pursued in other materials. Entering largely uncharted territory, time-resolved pump-probe Kerr rotation is used to explore the coherent spin dynamics of electrons and holes in bulk formamidinium caesium lead iodine bromide (FA0.9 Cs0.1 PbI2.8 Br0.2 ) and to determine key parameters characterizing interactions of their spins, such as the g-factors and relaxation times. The demonstrated long spin dynamics and narrow g-factor distribution prove the perovskites as promising competitors for conventional semiconductors in spintronics. The dynamic nuclear polarization via spin-oriented holes is realized and the identification of the lead (207 Pb) isotope in optically detected nuclear magnetic resonance proves that the hole-nuclei interaction is dominated by the lead ions. A detailed theoretical analysis accounting for the specifics of the lead halide perovskite materials allows the evaluation of the underlying hyperfine interaction constants, both for electrons and holes. Recombination and spin dynamics evidence that at low temperatures, photogenerated electrons and holes are localized at different regions of the perovskite crystal, resulting in their long lifetimes up to 44μs. The findings form the base for the tailored development of spin-optoelectronic applications for the large family of lead halide perovskites and theirnanostructures.
Highlights
The outstanding optical quality of lead halide perovskites inspires studies applications, as their quantum efficiency of their potential for the optical control of carrier spins as pursued in other materials
The (Cs) cation mixture became the state of demonstrated long spin dynamics and narrow g-factor distribution prove the perovskites as promising competitors for conventional semiconductors in spintronics
Still the fundamental physical properties are close to their parent structures, nuclear magnetic resonance proves that the hole–nuclei interaction is dominated by the lead ions
Summary
FA0.9Cs0.1PbI2.8Br0.2 perovskite crystals have a direct bandgap at the R-point (the cube corner along the [111]-direction) of the Brillouin zone. The low-temperature photoluminescence (PL) in Figure 1b with a maximum at 1.495 eV arises likely from bound excitons. The comparison of the decay of the differential reflectivity ΔR/R (probing the exciton population) and KR (probing the induced spin polarization), Figures 1c and 1d, respectively, show that their dynamics are strongly different. The spin dynamics measured by the extended pump–probe KR technique[40] in B|| = 100 mT show a mono-exponential decay with the longitudinal spin relaxation time T1 = 45 ns. It exceeds by an order of magnitude the population times indicating that resident carriers control the KR dynamics.[25]
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