  Floquet insulators are periodically driven quantum systems that can host
novel topological phases as a function of the drive parameters. These new
phases exhibit features reminiscent of fermion doubling in discrete-time
lattice fermion theories. We make this suggestion concrete by mapping the
spectrum of a noninteracting (1+1)D Floquet insulator for certain drive
parameters onto that of a discrete-time lattice fermion theory with a
time-independent Hamiltonian. The resulting Hamiltonian is distinct from the
Floquet Hamiltonian that generates stroboscopic dynamics. It can take the form
of a discrete-time Su-Schrieffer-Heeger model with half the number of spatial
sites of the original model, or of a (1+1)D Wilson-Dirac theory with one
quarter of the spatial sites.
