Unexpected electric-field-induced antiferroelectric liquid crystal phase in the Sm C^*_α temperature range and the discrete flexoelectric effect

The unique nanometer-sized helical structure in SmCα∗ may sometimes evolve continuously to the micrometer-sized one in SmC∗; conceivably ferroelectric SmCα∗ is to be unwound by an applied electric field. By drawing electric-field-induced birefringence contours in the field-temperature phase diagram and by studying the superlattice structure of the field-induced subphase with resonant x-ray scattering, we established that an applied field unexpectedly stabilizes the well-known antiferroelectric four-layer biaxial subphase as well as the other prototypal ferrielectric three-layer one in the SmCα∗ temperature range; the effective long-range interlayer interaction due to the discrete flexoelectric effect actually plays an important role in stabilizing not only the biaxial subphases but also the optically uniaxial SmCα∗ subphase, contrary to the notion that the competition between the direct interactions of the nearest-neighbor layers and those of the next-nearest-neighbor layers should be required for the nanometer-sized helical structure.