Abstract
This work reports the general design and characterization of two exotic, anomalous nonequilibrium topological phases. In equilibrium systems, the Weyl nodes or the crossing points of nodal lines 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 Floquet phases. The fascinating topological phases we obtain are previously unknown and can be experimentally studied using, for example, a three-dimensional lattice of coupled ring resonators.
Highlights
Owing to their rich features not available in equilibrium counterparts, the great potential of nonequilibrium topological phases is being widely recognized [1,2,3,4,5,6,7,8,9,10,11,12,13]
The physics is much more involving in nonequilibrium situations, because the Weyl nodes in Floquet higherorder Weyl semimetals (HOWSs) and the crossed nodal lines in Floquet higher-order nexus semimetals (HONSs) can feature exotic phase transitions between Floquet hybrid topological insulators (FHTI), anomalous Floquet topological insulators (AFI), and anomalous Floquet higher-order topological insulator (AFHOTI)
FHTI, AFI, and AFHOTI refer to the three distinct cases where the two quasienergy gaps support the chiral edge mode and topological corner mode in a hybrid manner, chiral edge modes only, and topological corner modes
Summary
Owing to their rich features not available in equilibrium counterparts, the great potential of nonequilibrium topological phases is being widely recognized [1,2,3,4,5,6,7,8,9,10,11,12,13]. In a traditional Weyl semimetal, the Weyl node represents the phase transition point between the Chern insulator and normal insulator of some 2D slices, so it supports the well-known surface Fermi arc upon opening up its boundary along one direction. In a HOWS [69,73,74,75] the Weyl node is the phase transition point between a Chern insulator and a higher-order topological insulator (HOTI). The physics is much more involving in nonequilibrium situations, because the Weyl nodes in Floquet HOWS and the crossed nodal lines in Floquet HONS can feature exotic phase transitions between Floquet hybrid topological insulators (FHTI), anomalous Floquet topological insulators (AFI), and anomalous Floquet higher-order topological insulator (AFHOTI). FHTI, AFI, and AFHOTI refer to the three distinct cases where the two quasienergy gaps support the chiral edge mode and topological corner mode in a hybrid manner, chiral edge modes only, and topological corner modes
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