Zhang Xiangzhe, Zhang Renyan, Wang Yizhi, Zhang Yi, Jiang Tian, Deng Chuyun, Zhang Xueao, Qin Shiqiao
College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha, 410073, People's Republic of China.
Nanotechnology. 2019 Oct 25;30(43):435702. doi: 10.1088/1361-6528/ab33e0. Epub 2019 Jul 19.
Monolayer graphene has high symmetrical crystal structure and exhibits in-plane isotropic physical properties. However, twisted bilayer graphene (tBLG) is expected to differ physically, due to the broken symmetry introduced by the interlayer coupling between adjacent graphene layers. This symmetry breaking is usually accompanied by in-plane anisotropy in their electrical, optical and thermal properties. However, the existence of in-plane anisotropy in tBLG has remained evasive until now. Here, an unambiguous identification of the in-plane anisotropy in tBLG is established by angle-resolved polarized Raman spectroscopy. It was found that the double-resonant two-dimensional band is anisotropic. The degree of in-plane anisotropy is found to be dependent on the misorientation angles, which is two- and four-fold for tBLG with misorientation angles of 15° and 20°, respectively. This finding adds a new dimension to the properties of graphene, which opens a possibility to the development of graphene-based angle-resolved photonics and electronics.
单层石墨烯具有高度对称的晶体结构，并表现出平面内各向同性的物理性质。然而，由于相邻石墨烯层之间的层间耦合引入了对称性破缺，扭曲双层石墨烯（tBLG）预计在物理性质上会有所不同。这种对称性破缺通常伴随着其电学、光学和热学性质的平面内各向异性。然而，到目前为止，tBLG中平面内各向异性的存在一直难以捉摸。在此，通过角分辨偏振拉曼光谱明确识别了tBLG中的平面内各向异性。研究发现双共振二维带是各向异性的。平面内各向异性的程度取决于取向差角，对于取向差角为15°和20°的tBLG，分别为两倍和四倍。这一发现为石墨烯的性质增添了新的维度，为基于石墨烯的角分辨光子学和电子学的发展开辟了可能性。
