This work reports the general design and characterization of two exotic, anomalous nonequilibrium gapless topological phases. In equilibrium systems, the Weyl nodes or the crossing points of nodal lines of three-dimensional systems may become the transition points between higher-order and first-order topological phases defined on two-dimensional slices, thus featuring both hinge Fermi arc and surface Fermi arc. We advance this concept by presenting a strategy to obtain, using time-sequenced normal insulator phases only, Floquet higher-order Weyl semimetals and Floquet higher-order nexus semimetals, where the concerned topological singularities in the three-dimensional Brillouin zone border anomalous two-dimensional higher-order topological phases. Our theoretical results stimulate and guide future experiments on higher-order semimetal phases using, for example, a three-dimensional lattice of coupled ring resonators.

中文翻译：

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Floquet 高阶 Weyl 和 nexus 半金属

这项工作报告了两个奇异的异常非平衡无间隙拓扑相的一般设计和表征。在平衡系统中，三维系统的外尔节点或节点线的交叉点可能成为二维切片上定义的高阶和一阶拓扑相之间的过渡点，从而具有铰链费米弧和表面费米弧。我们通过提出一种策略来推进这一概念，该策略仅使用时间顺序的正常绝缘体相获得 Floquet 高阶外尔半金属和 Floquet 高阶连接半金属，其中三维布里渊区中的相关拓扑奇点边界异常二维高阶拓扑相。我们的理论结果激发并指导了未来的高阶半金属相实验，例如，使用耦合环形谐振器的三维晶格。