Competition between ferroelectric and flexoelectric polarization in freelysuspended smectic films

We report a detailed ellipsometric study of freely suspended films of chira l liquid-crystal compounds possessing smectic-A and smectic-C phases. In th e temperature region between the smectic-A - smectic-C bulk and surface tra nsitions, a discontinuous reconstruction of the tilt profile across the fil m is observed in the presence of a constant d.c. electric field. Comparison of the measured ellipsometric quantities with values calculated from model tilt profiles reveals a competition between a structure possessing a homog eneous tilt direction and large ferroelectric polarization and a structure with opposite tilt direction in the two film halfs and large flexoelectric polarization.