  Particle shape and medium chirality are two key features recently used to
control anisotropic colloidal self-assembly and dynamics in liquid crystals.
Here, we study magnetically responsive gourd-shaped colloidal particles
dispersed in cholesteric liquid crystals with periodicity comparable or smaller
than the particle's dimensions. Using magnetic manipulation and optical
tweezers, which allow one to position colloids near the confining walls, we
measured the elastic repulsive interactions of these particles with confining
surfaces and found that separation-dependent particle-wall interaction force is
a non-monotonic function of separation and shows oscillatory behavior. We show
that gourd-shaped particles in cholesterics reside not on a single
sedimentation level, but on multiple long-lived metastable levels separated by
a distance comparable to cholesteric periodicity. Finally, we demonstrate
three-dimensional laser tweezers assisted assembly of gourd-shaped particles
taking advantage of both orientational order and twist periodicity of
cholesterics, potentially allowing new forms of orientationally and
positionally ordered colloidal organization in these media.
