Lead halide perovskites (LHPs) exhibit large spin–orbit coupling (SOC), leading to only twofold-degenerate valence and conduction bands and therefore allowing for efficient optical orientation. This makes them ideal materials to study charge carrier spins. With this study we elucidate the spin dynamics of photoexcited charge carriers and the underlying spin relaxation mechanisms in CsPbI₃ nanocrystals by employing time-resolved differential transmission spectroscopy (DTS). We find that the photoinduced spin polarization significantly diminishes during thermalization and cooling toward the energetically favorable band edge. Temperature-dependent DTS reveals a decay in spin polarization that is more than 1 order of magnitude faster at room temperature (3 ps) than at cryogenic temperatures (32 ps). We propose that spin relaxation of free charge carriers in large-SOC materials like LHPs occurs as a result of carrier–phonon scattering, as described by the Elliott–Yafet mechanism.

中文翻译：

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CsPbI3纳米晶体中自由载流子的自旋极化动力学。

卤化钙钛矿（LHPs）表现出大的自旋-轨道耦合（SOC），仅导致简并的二价化合价和导带，因此允许有效的光学取向。这使它们成为研究电荷载流子自旋的理想材料。通过这项研究，我们阐明了光激发电荷载体的自旋动力学及其在CsPbI _3中的潜在自旋弛豫机制。纳米晶体通过采用时间分辨差分透射光谱法（DTS）。我们发现，光诱导的自旋极化在热化和冷却过程中朝着能量上有利的能带边缘显着减小。依赖温度的DTS显示，自旋极化的衰减在室温（3 ps）处比在低温（32 ps）处快1个数量级。我们提出，如Elliott-Yafet机制所述，由于载子-声子的散射，大型SOC材料（如LHP）中的自由电荷载流子发生自旋弛豫。