Kopteva Nataliia E, Yakovlev Dmitri R, Yalcin Eyüp, Kalitukha Ina V, Akimov Ilya A, Nestoklon Mikhail O, Turedi Bekir, Hordiichuk Oleh, Dirin Dmitry N, Kovalenko Maksym V, Bayer Manfred
Experimentelle Physik 2, Technische Universität Dortmund, 44227, Dortmund, Germany.
Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Zürich, CH-8093, Switzerland.
Adv Sci (Weinh). 2025 Apr;12(15):e2416782. doi: 10.1002/advs.202416782. Epub 2025 Feb 20.
The great variety of lead halide perovskite semiconductors represents an outstanding platform for studying crystal symmetry effects on the spin-dependent properties. Access to them is granted through the optical orientation of exciton and carrier spins by circularly polarized photons. Here, the exciton spin polarization is investigated at 1.6 K cryogenic temperature in four lead halide perovskite crystals with different symmetries: (almost) cubic in FACsPbIBr and FAPbBr, and orthorhombic in MAPbI and CsPbBr. Giant optical orientation of 85% is found for the excitons in FACsPbIBr, MAPbI, and CsPbBr, while it amounts to 20% in FAPbBr. For all studied crystals, the optical orientation is robust to detuning of the laser photon energy from the exciton resonance, remaining constant for high energy detunings up to 0.3 eV, above which it continuously decreases to zero for detunings exceeding 1 eV. No acceleration of the spin relaxation for excitons with large kinetic energy is found in the cubic and orthorhombic crystals. This evidences the absence of the Dyakonov-Perel spin relaxation mechanism, which is based on the Rashba-Dresselhaus splitting of spin states at finite k-vectors. This indicates that the spatial inversion symmetry is maintained in perovskite crystals, independent of the cubic or orthorhombic phase.
多种铅卤化物钙钛矿半导体是研究晶体对称性对自旋相关特性影响的出色平台。通过圆偏振光子对激子和载流子自旋进行光学取向，可以获得这些材料。在此，在1.6 K低温下研究了四种具有不同对称性的铅卤化物钙钛矿晶体中的激子自旋极化：FACsPbIBr和FAPbBr为（近乎）立方晶系，MAPbI和CsPbBr为正交晶系。在FACsPbIBr、MAPbI和CsPbBr中发现激子的巨大光学取向达到85%，而在FAPbBr中为20%。对于所有研究的晶体，光学取向对激光光子能量与激子共振的失谐具有鲁棒性，在高达0.3 eV的高能量失谐下保持恒定，超过1 eV时，随着失谐增加它会持续降至零。在立方晶系和正交晶系晶体中未发现具有大动能的激子的自旋弛豫加速现象。这证明不存在基于有限k矢量处自旋态的Rashba-Dresselhaus分裂的Dyakonov-Perel自旋弛豫机制。这表明钙钛矿晶体中保持了空间反演对称性，与立方相或正交相无关。
