State Key Lab for Mesoscopic Physics and School of Physics, Peking University, Beijing, 100871, China.
Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China.
Sci Rep. 2017 May 11;7(1):1758. doi: 10.1038/s41598-017-01874-2.
The recently discovered two-dimensional (2D) semimetal 1 T´-MoTe exhibits colossal magnetoresistance and superconductivity, driving a strong research interest in the material's quantum phenomena. Unlike the typical hexagonal structure found in many 2D materials, the 1 T´-MoTe lattice has strong in-plane anisotropy. A full understanding of the anisotropy is necessary for the fabrication of future devices which may exploit these quantum and topological properties, yet a detailed study of the material's anisotropy is currently lacking. While angle resolved Raman spectroscopy has been used to study anisotropic 2D materials, such as black phosphorus, there has been no in-depth study of the Raman dependence of 1 T´-MoTe on different layer numbers and excitation energies. Here, our angle resolved Raman spectroscopy shows intricate Raman anisotropy dependences of 1 T´-MoTe on polarization, flake thickness (from single layer to bulk), photon, and phonon energies. Using a Paczek approximation, the anisotropic Raman response can be captured in a classical framework. Quantum mechanically, first-principle calculations and group theory reveal that the anisotropic electron-photon and electron-phonon interactions are nontrivial in the observed responses. This study is a crucial step to enable potential applications of 1 T´-MoTe in novel electronic and optoelectronic devices where the anisotropic properties might be utilized for increased functionality and performance.
最近发现的二维（2D）半金属 1T´-MoTe 表现出巨大的磁电阻和超导性，这激发了人们对该材料量子现象的强烈研究兴趣。与许多 2D 材料中常见的六边形结构不同，1T´-MoTe 晶格具有强烈的面内各向异性。为了制造可能利用这些量子和拓扑性质的未来器件，全面了解各向异性是必要的，但目前对该材料各向异性的详细研究还很缺乏。尽管角分辨拉曼光谱已被用于研究各向异性 2D 材料，如黑磷，但对 1T´-MoTe 在不同层数和激发能下的拉曼依赖性还没有深入研究。在这里，我们的角分辨拉曼光谱显示了 1T´-MoTe 在极化、薄片厚度（从单层到体相）、光子和声子能量等方面的复杂拉曼各向异性依赖性。使用 Paczek 近似，可以在经典框架中捕获各向异性拉曼响应。从量子力学的角度来看，第一性原理计算和群论表明，在观察到的响应中，电子-光子和电子-声子的各向异性相互作用是非平凡的。这项研究是实现 1T´-MoTe 在新型电子和光电子器件中潜在应用的关键步骤，其中各向异性特性可能用于提高功能和性能。
