  Backscattering-immune chiral modes arise along certain line defects in
three-dimensional materials. In this paper, we study Floquet chiral modes along
Floquet topological defects, namely, the defects come entirely from spatial
modulations of periodic driving. We define a precise topological invariant that
counts the number of Floquet chiral modes, which is expressed as an integral on
a five-dimensional torus parameterized by $(k_x,k_y,k_z,\theta,t)$. This work
demonstrates the possibility of creating chiral modes in three-dimensional bulk
materials by modulated driving. We hope that it will stimulate further studies
of Floquet topological defects.
