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.