The local structure of a two-dimensional layered material, Bi₂Rh₃Se₂, in which superconducting (SC) and charge-density wave (CDW) states coexist, was investigated using Bi Lα and Lγ X-ray fluorescence holography (XFH). The crystal of Bi₂Rh₃Se₂ adopts a monoclinic lattice with a space group of C2/m (No. 12) at room temperature; however, the structure below the CDW transition (∼240 K) is still unclear because of the difficulty in analyzing single-crystal X-ray diffraction. Therefore, information on the crystal structure below 240 K is significant to fully investigate the relationship between the SC and CDW states. Precisely, the value of β has not been definitely determined, i.e., β ∼ 90° or ∼134° is still unclear. Therefore, the crystal structure above 240 K is still under discussion. In this study, we attempted to determine the crystal structure at 300 and 200 K by comparing the atomic images reconstructed from Bi Lγ holograms with images simulated based on crystal structure models. A Bi Lα hologram was also exploited to determine suitable atomic locations by comparison with the simulated ones. The atomic image simulated with the crystal structure of Bi₂Rh₃S₂ below the structural phase transition temperature reproduced well the experimental atomic image at 200 K. Specifically, the line profiles of the reconstructed images at 300 and 200 K, which exactly reflect the intensity of the atomic spots, clearly indicate the structural variation above and below the CDW transition temperature, i.e., the supercell structure is suggested as the atomic location for Bi₂Rh₃Se₂ below the CDW transition temperature.

中文翻译：

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Bi Lα 和 Lγ X 射线荧光全息术测定 Bi2Rh3Se2 上下电荷密度波跃迁的结构


使用 Bi Lα 和 Lγ X 射线荧光全息术 （XFH） 研究了二维层状材料 Bi₂Rh₃Se₂ 的局部结构，其中超导 （SC） 和电荷密度波 （CDW） 状态共存。Bi₂Rh₃Se₂ 的晶体在室温下采用空间群为 C2/m（12 号）的单斜晶格;然而，由于难以分析单晶 X 射线衍射，CDW 跃迁 （∼240 K） 以下的结构仍不清楚。因此，关于低于 240 K 的晶体结构的信息对于全面研究 SC 和 CDW 状态之间的关系具有重要意义。确切地说，β的值尚未确定，即 ∼ 90° 或 ∼134° β仍然不清楚。因此，240 K 以上的晶体结构仍在讨论中。在这项研究中，我们试图通过将 Bi Lγ 全息图重建的原子图像与基于晶体结构模型模拟的图像进行比较来确定 300 K 和 200 K 下的晶体结构。还利用 Bi Lα 全息图通过与模拟原子位置进行比较来确定合适的原子位置。在结构相变温度以下，用 Bi₂Rh₃S₂ 的晶体结构模拟的原子图像很好地再现了 200 K 下的实验原子图像。 具体来说，重建图像在 300 K 和 200 K 下的线剖面准确反映了原子点的强度，清楚地表明了 CDW 转变温度以上和以下的结构变化，即超胞结构被认为是 Bi₂Rh₃Se₂ 低于 CDW 转变温度的原子位置。