Nonlinear effects in the dielectric response of ferroelectric liquid crystals

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Abstract
The unwinding of the helicoidal structure of ferroelectric liquid crystals by a static electric field is studied theoretically in the constant amplitude approximation. The field dependence of the pitch, of the induced polarization and of the static dielectric susceptibility is evaluated. Close to Tc nonlinear effects in the susceptibility become important and the dielectric susceptibility, which is defined as the susceptibility in the limit of small fields is hard to evaluate experimentally, simply because it is hard to perform experiments at sufficiently small fields. By our calculation we present a way to get around this problem and we show how to determine the Goldstone mode dielectric susceptibility also if comparatively large fields are used in an experiment.