Dynamic metal at the grain boundary of Floquet topological insulators

Driven quantum materials often feature emergent topology solely arising from the time periodic drive, otherwise absent in static crystals, among which the dynamic bulk-boundary correspondence encoded by nondissipative gapless modes residing near the Floquet zone center and/or boundaries are the most prominent ones. Here we show that such dynamic topological crystal can harbor topologically robust gapless matallic state along the grain boundary in its interior when the Floquet-Bloch band inversion occurs at a finite momentum (K_inv), such that the Burgers vector (b) of the constituting array of dislocations satisfies K_inv·b = π (modulo 2π). Such in-gap topological bulk metal, which can appear at the center and/or edge of the underlying periodic Floquet Brillouin zone, results from the hybridization among the localized modes bound to the core of individual dislocation. We exemplify these general outcomes by considering a paradigmatic representative of time-reversal symmetry breaking two-dimensional insulating system. Possible experimental setup underpinning such emergent driven topological metallic states in real materials are also discussed.