Optical Access to Electron and Hole Spins in Lead Halide Perovskite Crystals and Nanocrystals

The exceptional optical quality of lead halide perovskites inspires studies of their potential for optical control of carrier spins, a pursuit that has been undertaken in other materials. The Landé factors (g-factors) of charge carriers are of significant importance in solids, controlling spin-dependent phenomena and providing insights into the electronic band structure. We present a comprehensive set of experimental data on the values and anisotropies of the electron and hole g-factors for a representative set of perovskites, including hybrid organic-inorganic and all-inorganic lead halide perovskites with the band gap energy varying from 1.5 to 3.2 eV. The studies include bulk crystals [1,2], nanocrystals [3] and 2D structures [4,5]. The electron and hole g-factors were determined by measuring the Zeeman splitting of electrons and holes using the spin-flip Raman scattering technique at a cryogenic temperature of 1.6 K and in a magnetic field up to 10 T. Furthermore, the spin relaxation and spin coherence times were studied via time-resolved Kerr rotation. We employ principal density functional theory (DFT) calculations in conjunction with tight-binding and k●p approaches to calculate the Landé factors in bulk [2] and 2D perovskites. Our findings illustrate the universal dependence of the electron and hole g-factor on the band gap energy across the diverse perovskite material classes.<br/>We further demonstrate that the degree of optical orientation of carrier spins by circularly polarized light is highly stable against detuning of the laser photon energy from the band gap by up to 0.25 eV. This evidence suggests that spin relaxation mechanisms for free carriers are inefficient during their energy relaxation and thus spin relaxation for localized electrons and holes is provided by the hyperfine interaction with the nuclear spins [6,7]. The dynamic nuclear polarization via spin-oriented holes has been successfully realized. The lead (²⁰⁷Pb) isotope has been identified optically by spin-flip Raman scattering in corresponding changes of the hole Zeeman splitting. This evidence demonstrates that the hole–nuclei interaction is dominated by the lead ions whilst the hyperfine interaction between electrons and nuclei is considerably weaker. In 2D perovskites, a Overhauser field of up to 0.6 T can be observed, due to the high contrast of hyperfine splitting in respect to the Zeeman splitting [4]. A detailed theoretical analysis of the specific properties of lead halide perovskite materials allows the evaluation of the underlying hyperfine interaction constants, both for electrons and holes.<br/>The tunability of the band gap, the long spin dynamics and the narrow g-factor distribution demonstrate that perovskites are promising competitors for conventional semiconductors in spintronics.<br/><br/>References<br/>[1] E. Kirstein, et al., Lead-dominated hyperfine interaction impacting the carrier spin dynamics in halide perovskites, Advanced Materials 34, 2105263 (2022)<br/>[2] E. Kirstein, et al., The Landé factors of electrons and holes in lead halide perovskites: universal dependence on the band gap, Nature Communications 13, 3062 (2022)<br/>[3] P. S. Grigoryev, et al., Coherent spin dynamics of electrons and holes in CsPbBr₃ colloidal nanocrystals, Nano Letters 21, 8481 (2021)<br/>[4] C. Harkort, et al., Spin-Flip Raman Scattering on Electrons and Holes in Two-Dimensional (PEA)₂PbI₄ Perovskites, Small. 19(32), e2300988 (2023)<br/>[5] E. Kirstein, et al., Coherent spin dynamics of electrons in two-dimensional (PEA)₂PbI₄ perovskites, Nano Letters 23, 205 (2023)<br/>[6] N. E. Kopteva, et al., Highly-Polarized Emission Provided by Giant Optical Orientation of Exciton Spins in Lead Halide Perovskite Crystals, Advanced<i> Science</i> , 2403691 (2024)<br/>[7] D. Kudlacik, et al., Optical Spin Orientation of Localized Electrons and Holes Interacting with Nuclei in a FA_0.9Cs_0.1PbI_2.8Br_0.2 Perovskite Crystal, <i>ACS Photonics</i> (2024)