Hyperfine interaction of electrons and holes with nuclei probed by optical orientation in MAPbI$_3$ perovskite crystals

TL;DR

The paper investigates how hyperfine interaction with nuclear spins controls spin dynamics of localized electrons and holes in MAPbI3 at cryogenic temperatures using optical orientation, Hanle, and polarization-recovery measurements. By decomposing the signals into contributions from strongly localized holes, localized electrons, and weakly localized holes, the authors quantify nuclear-spin fluctuations and demonstrate dynamic nuclear polarization, with Overhauser fields up to about 5 mT for electrons and −30 mT for holes and a light-induced nuclear build-up time of about 11 s. The study shows that carrier correlation times with nuclear spin fluctuations exceed spin lifetimes (τ_c > T_s) and that delocalization at higher temperatures suppresses the nuclear-spin mediated relaxation, leaving intrinsic spin lifetimes as the determinant. These findings provide fundamental insight into spin interactions in perovskites and establish a basis for manipulating nuclear polarization in MAPbI3 for spintronic and quantum-information applications.

Abstract

Optical orientation of electron and hole spins by circularly polarized light is investigated for MAPbI$_3$ single crystals. The Hanle and polarization recovery effects measured in transverse and longitudinal magnetic fields, respectively, evidence the hyperfine interaction with nuclear spins as the main factor determining the spin dynamics of charge carriers at cryogenic temperatures. The parameters of the nuclear spin fluctuations within the carrier localization volume are evaluated. Dynamic polarization of the nuclear spins is demonstrated by the Overhauser field reaching 5 mT for acting on the electrons and -30 mT for acting on the holes.

Figures (7)

• Figure 1: (a) Polarized photoluminescence spectra measured on a MAPbI$_3$ crystal at $T = 1.6$ K. The laser helicity is modulated between $\sigma^+$ and $\sigma^-$ at 400 kHz, while the detection polarization is fixed at $\sigma^+$. Laser photon energy $E_{\rm exc}=1.722$ eV with power $P=18$ W/cm$^2$. The dashed gray line indicates the free exciton energy, $E_{\rm X}=1.636$ eV, measured in reflectivity, see Ref. kopteva2025optical. (b) Spectral dependence of the optical orientation degree, evaluated according to Eq. \ref{['eq:optical_orientation_degree_modulated']} from the spectra shown in panel (a).
• Figure 2: Hanle and polarization recovery curves measured in Voigt or Faraday geometry at $T=1.6$ K for (a) $E_{\rm det}=1.638$ eV and (b) 1.628 eV photon detection energy. The laser light helicity is modulated at 400 kHz, with $E_{\rm exc} = 1.722$ eV and $P = 18$ W/cm$^2$. The dashed lines show the individual contributions of strongly localized holes (red), electrons (green), and weakly localized holes (orange). Their parameters are given in Table \ref{['tab:comparison_spectral']}.
• Figure 3: Spectral dependence of the parameters evaluated from the polarization recovery and Hanle curves, measured at $T=1.6$ K. The excitation laser helicity is modulated at 400 kHz, with $E_{\rm exc} = 1.722$ eV and $P = 18$ W/cm$^2$. (a,b) Optical orientation degree measured at zero field (orange) and 120 mT (blue). (c-f) Amplitudes and half-widths of the respective components for strongly localized holes (red), electrons (green), and weakly localized holes (orange). In all panels, the symbols give the experimental data and the lines are guides for the eye.
• Figure 4: Polarization recovery and Hanle curves measured at $T = 15$ K with $\sigma^+/\sigma^-$ excitation modulated at 400 kHz for two detection energies, (a) $E_{\rm det} = 1.638$ eV and (b) $E_{\rm det} = 1.628$ eV. $P = 18$ W/cm$^2$ and $E_{\rm exc} = 1.722$ eV. The dashed lines show the individual contributions of strongly localized holes (red), electrons (green), and weakly localized holes (orange).
• Figure 5: Temperature dependence of the parameters evaluated from the polarization recovery and Hanle curves measured at $E_{\rm det}=1.628$ eV. The circular laser helicity is modulated at 400 kHz. $E_{\rm exc}=1.722$ eV and $P=18$ W/cm$^2$. (a,b) Total optical orientation degree measured at zero field (orange) and 120 mT (blue). (c-f) Amplitudes and HWHMs of the respective components of strongly localized holes (red), electrons (green), and weakly localized holes (orange). In all panels, the symbols give the experimental data and the lines are guides to the eye.