The Landé or g-factors of charge carriers are decisive for the spin-dependent phenomena in solids and provide also information about the underlying electronic band structure. We present a comprehensive set of experimental data for values and anisotropies of the electron and hole Landé factors in hybrid organic-inorganic (MAPbI3, MAPb(Br0.5Cl0.5)3, MAPb(Br0.05Cl0.95)3, FAPbBr3, FA0.9Cs0.1PbI2.8Br0.2, MA=methylammonium and FA=formamidinium) and all-inorganic (CsPbBr3) lead halide perovskites, determined by pump-probe Kerr rotation and spin-flip Raman scattering in magnetic fields up to 10 T at cryogenic temperatures. Further, we use first-principles density functional theory (DFT) calculations in combination with tight-binding and k ⋅ p approaches to calculate microscopically the Landé factors. The results demonstrate their universal dependence on the band gap energy across the different perovskite material classes, which can be summarized in a universal semi-phenomenological expression, in good agreement with experiment.

interest has been boosted by photovoltaic applications, as their quantum efficiency has reached 25.5% [1] but also extending to radiation-sensing [2,3] and a variety of optoelectronic devices. [4][5][6][7] Reaching the limits of high-quality MAPbI 3 , FAPbI 3 , and CsPbI 3 single crystals, combined structures with MA, FA, and caesium (Cs) cation mixture became the state of the art perovskite materials, increasing quantum efficiency and prolonging structural stability from days to months. [2,[8][9][10] Still the fundamental physical properties are close to their parent structures, thus the presented FA 0.9 Cs 0.1 PbI 2.8 Br 0.2 acts as a valid model system for the class of lead halide perovskites.Compared to conventional III-V and II-VI semiconductors, the perovskites have in some sense an inverted band structure: the valence band (VB) states are formed by s-orbitals, while the conduction band (CB) states are contri buted by p-orbitals. The strong spin-orbit coupling and in particular the Rashba effect, [11][12][13][14] also exchanges the spin properties of electrons and holes. [15,16] As a consequence, the hyperfine interaction with the lattice nuclei is dominated by the holes and not by the electrons.The perovskite band structure gives clean polarization selection rules for the optical transitions so that in combinationThe 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 pumpprobe Kerr rotation is used to explore the coherent spin dynamics of electrons and holes in bulk formamidinium caesium lead iodine bromide (FA 0.9 Cs 0.1 PbI 2.8 Br 0.2 ) 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 44 μs. The findings form the base for the tailored development of spin-optoelectronic applications for the large family of lead halide perovskites and their nanostructures.

The versatile potential of lead halide perovskites and two-dimensional materials is merged in the Ruddlesden− Popper perovskites having outstanding optical properties. Here, the coherent spin dynamics in Ruddlesden−Popper (PEA) 2 PbI 4 perovskites is investigated by picosecond pump−probe Kerr rotation in an external magnetic field. The Larmor spin precession of resident electrons with a spin dephasing time of 190 ps is identified. The longitudinal spin relaxation time in weak magnetic fields measured by the spin inertia method is as long as 25 μs. A significant anisotropy of the electron g-factor with the in-plane value of +2.45 and out-of-plane value of +2.05 is found. The exciton out-of-plane g-factor of +1.6 is measured by magnetoreflectivity. This work contributes to the understanding of the spindependent properties of two-dimensional perovskites and their spin dynamics.

The coherent spin dynamics of fluorine donor-bound electrons in ZnSe induced by pulsed optical excitation is studied in a perpendicular applied magnetic field. The Larmor precession frequency serves as a measure for the total magnetic field exerted onto the electron spins and, surprisingly, does not increase linearly with the applied field, but shows a step-like behavior with pronounced plateaus, given by multiples of the laser repetition rate. This discretization occurs by a feedback mechanism in which the electron spins polarize the nuclear spins, which in turn generate a local Overhauser field adjusting the total magnetic field accordingly. Varying the optical excitation power, we can control the plateaus, in agreement with our theoretical model. From this model, we trace the observed discretization to the optically induced Stark field, which causes the dynamic nuclear polarization.

The periodic optical orientation of electron spins in (In,Ga)As/GaAs quantum dots leads to the formation of electron spin precession modes about an external magnetic field which are resonant with the pumping periodicity. As the electron spin is localized within a nuclear spin bath, its polarization imprints onto the spin polarization of the bath. The latter acts back on the electron spin polarization. We implement a pulse protocol where a train of laser pulses is followed by a long, dark gap. It allows us to obtain a high-resolution precession mode spectrum from the free evolution of the electron spin polarization. Additionally, we vary the number of pump pulses in a train to investigate the build-up of the precession modes. To separate out nuclear effects, we suppress the nuclear polarization by using a radio-frequency field. We find that a long-living nuclear spin polarization imprinted by the periodic excitation significantly speeds up the buildup of the electron spin polarization and induces the formation of additional electron spin precession modes. To interpret these findings, we extend an established dynamical nuclear polarization model to take into account optically detuned quantum dots for which nuclear spins activate additional electron spin precession modes.