Angle-resolved polarized Raman spectroscopy (ARPRS) is widely used to determine the crystal orientations of anisotropic layered materials (ALMs), which is an essential step to study all of their anisotropic properties. However, the understanding of the ARPRS response of black phosphorous (BP) as a most widely studied ALM is still unsatisfactory. Here, we clarify two key controversies about the physical origin of the intricate ARPRS response and the determination of crystal orientations in BP. Through systematic ARPRS measurements, we show that the degree of anisotropy of the response evolves gradually and periodically with the BP thickness, eventually leading to the intricate response. Meanwhile, we find that using the Raman peak intensity ratio of the two A_g phonon modes, the crystal orientations of BP can be unambiguously distinguished via a concise inequality . Comprehensive analysis and first-principles calculations reveal that the external anisotropic interference effect and the intrinsic electron–phonon coupling are responsible for the observations.

中文翻译：

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通过角分辨偏振拉曼光谱明确确定黑磷中的晶体取向

角度分辨偏振拉曼光谱 (ARPRS) 被广泛用于确定各向异性层状材料 (ALM) 的晶体取向，这是研究其所有各向异性特性的重要步骤。然而，对黑磷（BP）作为研究最广泛的 ALM 的 ARPRS 响应的理解仍然不能令人满意。在这里，我们澄清了关于复杂 ARPRS 响应的物理起源和 BP 中晶体取向的确定的两个关键争议。通过系统的 ARPRS 测量，我们表明响应的各向异性程度随着 BP 厚度逐渐且周期性地演变，最终导致复杂的响应。同时，我们发现利用两个 A _g的拉曼峰强度比声子模式，BP 的晶体取向可以通过简明的不等式明确区分。综合分析和第一性原理计算表明，外部各向异性干涉效应和本征电子-声子耦合是造成观测结果的原因。