Large magnetic optical rotary dispersion (Faraday rotation) has been demonstrated recently in methylammonium lead bromide. Here, we investigate the prospect of extending the active spectral range by altering the halogen. We also investigate the origins of large Faraday rotation in these diamagnetic materials using magnetic circular dichroism (MCD) spectroscopy and the Kramers–Kronig relations. We find that, while MAPbCl₃ (MA = methylammonium) single crystals exhibit a large Verdet constant in the blue, no appreciable Faraday rotation is observed in the red/near infra-red for MAPbI₃ single crystals. However, in all film samples, we find clear evidence of large MCD resulting from the Zeeman splitting of the highly resonant 1s exciton state. Our Kramers–Kronig calculations of Faraday rotation based on MCD data matches well with the dispersion of our experimental data for MAPbCl₃ and MAPbBr₃, with some deviation in magnitude—demonstrating the excitonic nature of Faraday rotation in these materials. However, our calculations predict significant Faraday rotation in MAPbI₃, contrary to our experimental results, indicating a potential discrepancy between the properties of the thin film and single crystal.

中文翻译：

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甲基铵卤化铅钙钛矿中的磁性旋光色散和磁性圆二色性

最近在甲基溴化铅中证明了大磁性光学旋转色散（法拉第旋转）。在这里，我们研究了通过改变卤素来扩展活性光谱范围的前景。我们还使用磁性圆二色性 (MCD) 光谱和 Kramers-Kronig 关系研究了这些抗磁性材料中大法拉第旋转的起源。我们发现，虽然 MAPbCl ₃（MA = 甲基铵）单晶在蓝色中表现出很大的 Verdet 常数，但在 MAPbI ₃的红色/近红外中没有观察到明显的法拉第旋转单晶。然而，在所有薄膜样品中，我们发现了由高度共振的 1s 激子态的塞曼分裂产生的大 MCD 的明确证据。我们基于 MCD 数据对法拉第旋转的 Kramers-Kronig 计算与我们的 MAPbCl ₃和 MAPbBr ₃实验数据的离散度非常匹配，但在幅度上存在一些偏差——证明了这些材料中法拉第旋转的激子性质。然而，我们的计算预测了 MAPbI _{3 中的}显着法拉第旋转，这与我们的实验结果相反，表明薄膜和单晶的特性之间存在潜在差异。