标题： 卤化铅钙钛矿晶体对激子光学取向的影响 显示英文标题

标题： Effect of crystal symmetry of lead halide perovskites on the optical orientation of excitons

摘要： 铅卤化物钙钛矿半导体的多样性代表了一个研究晶体对称性对自旋相关特性影响的优秀平台。通过圆偏振光对激子和载流子自旋进行光学取向可以获得它们。 此处，在$1.6$ K低温下研究了四种不同对称性的铅卤钙钛矿晶体中的激子自旋极化：FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$和 FAPbBr$_3$接近立方结构，而 MAPbI$_3$和 CsPbBr$_3$为正交结构。 在FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$、MAPbI$_3$和 CsPbBr$_3$中发现激子的巨光学取向为85%，而在FAPbBr$_3$中仅为20%。 对于所有研究的晶体，光学取向对激光光子能量偏离激子共振具有鲁棒性，在高能偏移下保持恒定，直到0.3 eV以上，超过1 eV的偏移则连续下降至零。 在立方和正交晶体中未发现具有大动能的激子自旋弛豫加速现象。 这证明了Dyakonov-Perel自旋弛豫机制的缺失，该机制基于有限$k$-矢量处自旋态的Rashba-Dresselhaus分裂。 这表明在钙钛矿晶体中，空间反演对称性得以保持，无论其是立方相还是正交相。 显示英文摘要

摘要： 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 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 FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$ and FAPbBr$_3$, and orthorhombic in MAPbI$_3$ and CsPbBr$_3$. Giant optical orientation of 85\% is found for the excitons in FA$_{0.9}$Cs$_{0.1}$PbI$_{2.8}$Br$_{0.2}$, MAPbI$_3$, and CsPbBr$_3$, while it amounts to 20\% in FAPbBr$_3$. 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.