Floquet Weyl

The expert knows: Most topological band effects can be cast to the quantum Hall effect in one way or the other. The surface arcs for Weyl-semimetals are no exception. Except that they are: Floquet physics can leave its fingerprints also here.

Weyl systems have doubly degenerate touching points with a linear dispersion away from them in their band structure. The low-energy excitations around this nodal points behave like Weyl fermions. Moreover, each Weyl point has an associated topological charge and the non-trivial topology manifests as Fermi arcs at the sample's surface: open Fermi surfaces connecting the surface projections of two Weyl points with opposite topological charges.

Fermi arcs are conventionally understood in terms of a layer Chern number. In this work, we show that Fermi arcs exists even when such an interpretation breaks down. This scenario can be achieved by periodically driving Weyl semimetals.

We put forward a simple toy model with anomalous Fermi arcs that cannot be understood in terms of a layer Chern number. Similar anomalous states in periodically driven systems have been predicted in 2D Chern insulators and shown to display surprising robustness against disorder. We believe that our anomalous Fermi arcs have the potential to extend similar disorder physics to three dimensions.