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 particlewall 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.
In the quasiclassical approximation we analyze the dependences of the resistivity ρ and Hall field on the magnetic field orientation and intensity in layered conductors with quasi-2D energy spectrum of arbitrary form. The Shubnikov-de Haas amplitudes are shown to drop abruptly and the smooth part of magnetoresistance to increase at certain orientation of H when the respective extreme (Fermi surface) FS cross section is self-intersecting. Anisotropy of ρ, depending essentially on FS topology, manifests itself most when the current flows across the layers
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