Existence of a topological Dirac nodal loop is predicted for hydrogenated monolayer boron sheets with a non-symmorphic symmetry. The three-center two-electron bonds in boron compounds restrict the electronic system to be insulating or semi-metallic with a Dirac nodal loop. Two types of electronic structures are distinguished by ${\mathbb{Z}}_2$ topological index, and confirmed by first-principles total-energy calculations. The topological taxonomy, developed in this research, can be applied to other two-dimensional materials and to seek novel Dirac fermions.

中文翻译：

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非对称氢化单层硼的拓扑狄拉克节点环

对于具有非对称对称性的氢化单层硼片，预测了拓扑狄拉克节点环的存在。硼化合物中的三中心双电子键将电子系统限制为具有Dirac节点环的绝缘或半金属。两种电子结构的区别在于${\mathbb{Z}}_2$拓扑指数，并通过第一性原理总能量计算得到证实。在这项研究中开发的拓扑分类法可以应用于其他二维材料，并寻找新颖的狄拉克费米子。