Low-symmetry 2D materials---such as ReS$_2$ and ReSe$_2$ monolayers, black phosphorus monolayers, group-IV monochalcogenide monolayers, borophene, among others---have more complex atomistic structures than the honeycomb lattices of graphene, hexagonal boron nitride, and transition metal dichalcogenides. The reduced symmetries of these emerging materials give rise to inhomogeneous electron, optical, valley, and spin responses, as well as entirely new properties such as ferroelasticity, ferroelectricity, magnetism, spin-wave phenomena, large nonlinear optical properties, photogalvanic effects, and superconductivity. Novel electronic topological properties, nonlinear elastic properties, and structural phase transformations can also take place due to low symmetry. The "Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials" Special Topic was assembled to highlight recent experimental and theoretical research on these emerging materials.

中文翻译：

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超越石墨烯：低对称性和各向异性二维材料

低对称性二维材料——例如 ReS$_2$ 和 ReSe$_2$ 单层、黑磷单层、IV 族单硫属化物单层、硼烯等——具有比石墨烯的蜂窝晶格更复杂的原子结构，六方氮化硼和过渡金属二硫属化物。这些新兴材料的对称性降低会产生不均匀的电子、光、谷和自旋响应，以及全新的特性，如铁弹性、铁电、磁性、自旋波现象、大型非线性光学特性、光电效应和超导性. 由于低对称性，还可以发生新的电子拓扑特性、非线性弹性特性和结构相变。“超越石墨烯：低对称性和各向异性二维材料”