QUANTIZED GRAIN-BOUNDARIES IN BENT SMECTIC-A LIQUID-CRYSTAL

In the smectic-A phase, close to the nematic-smectic-A transition, we observe under imposed bend planar defects walls separating two well-oriented ''grains''. Across the walls, the orientation presents quantized jump, of weak temperature-dependent amplitude. With a Landau model we explain the existence of these quantized grain boundaries from the high anisotropy of the bent smectic A. These planar defects have no analogue for twisted smectics, nor for superconductors.