The stacking order of 2D materials can result in fascinating physical properties. Two different stacking orders (AA and AB) were recently identified in ReS₂, a rising star in the transition metal dichalcogenides family with a unique anisotropic property. Their optical and vibrational properties show drastically different features. With intensity-scan spectrometry, the nonlinear optical absorption of both AA and AB stackings in ReS₂ was investigated. Saturable absorption (SA) only occurs in AB stacking at certain polarization angles, whereas it is absent in AA stacking. This saturation behavior is attributed to strong exciton–exciton annihilation (EEA). Excited-state absorption (ESA) is prominent in both stacking orders, but more anisotropic with polarization in AB stacking. Our results provide new insights in using ReS₂ as a nonlinear optical material in forefront optoelectronics.

中文翻译：

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堆积顺序驱动ReS _2的非线性光学吸收

2D材料的堆叠顺序可导致令人着迷的物理性能。最近在ReS _2中发现了两种不同的堆积顺序（AA和AB），这是过渡金属二卤化钨家族中的后起之秀，具有独特的各向异性。它们的光学和振动特性显示出截然不同的特征。使用强度扫描光谱法，ReS _2中AA和AB堆叠的非线性光学吸收被调查了。饱和吸收（SA）仅在某些偏振角的AB堆叠中发生，而在AA堆叠中则不存在。这种饱和行为归因于强激子-激子an灭（EEA）。激发态吸收（ESA）在两个堆叠顺序中均很突出，但在AB堆叠中具有更大的各向异性。我们的结果为将ReS ₂用作前沿光电器件中的非线性光学材料提供了新的见解。