Breakdown of boundary criticality and exotic topological semimetals in $\mathcal{P}\mathcal{T}$-invariant systems

Abstract: It was recently found that, going beyond the tendfold Altland-Zirnbauer symmetry classes and violating the bulk-boundary correspondence of the usual topological phases, PT-invariant systems support a real Chern insulator with the so-called boundary criticality, which forbids the transition between different orders of topological phases accompanied by the closing and reopening of the bulk-band gap. Here, we fnd that the periodic driving can break the boundary criticality of a PT-invariant system. Setting free from the the boundary criticality, diverse first- and second-order topological phases absent in the static case are found in both the zero and Pi/T modes. The application of our result in the three-dimensional PT-invariant system permits us to discover exotic second-order Dirac and nodal-line semimetals with coexisting surface and hinge Fermi arcs. Enriching the family of the topological phases in PT-invariant systems, our result provides us a useful way to explore novel topological phases.