NONLINEAR DIELECTRIC SUSCEPTIBILITY IN BLUE PHASES OF CHIRAL LIQUID-CRYSTALS

The deformation of the cubic blue phase I along the field changes from dilatation to compression or vice versa when the electric field vecto r is rotated from one crystallographic direction to another. This phen omenon is termed anomalous electrostriction and together with topology of phase diagrams of the blue phases awaits elucidation. Standard the ory of blue phases is not able to explain these observations. Followin g the experiments of Pieranski et al. we generalized the standard theo ry by incorporating a nonlinear dielectric susceptibility tensor (NDS) . It is shown that the distortion of the cubic blue phase I in the pre sence of the NDS may display the anomalous electrostriction, in accord ance with experiment. These results seem to indicate that nonlinear su sceptibility tensor is a relevant order parameter for the blue phases.