  Chiral active particles (CAPs) are self-propelling particles that break
time-reversal symmetry by orbiting or spinning, leading to intriguing
behaviors. Here, we examined the dynamics of CAPs moving in 2D lattices of disk
obstacles through active Brownian dynamics simulations and granular experiments
with grass seeds. We find that the effective diffusivity of the CAPs is
sensitive to the structure of the obstacle lattice, a feature absent in achiral
active particles. We further studied the transport of CAPs in obstacle arrays
under an external field and found a reentrant directional locking effect, which
can be used to sort CAPs with different activities. Finally, we demonstrated
that the parallelogram lattice of obstacles without mirror symmetry can
separate clockwise and counter-clockwise CAPs. The mechanisms of the above
three novel phenomena are qualitatively explained. As such, our work provides a
basis for designing chirality-based tools for single-cell diagnosis and
separation, and active particle-based environmental sensors.
