INDUCED POLARIZATION IN THE SmA*-PHASE: A COMPARISON OF THEORETICAL MODELS AND EXPERIMENTAL METHODS

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Abstract
When measuring the polarization of a ferroelectric liquid crystal one usually obtains quite a pronounced tail P (T) going well into the SmA*-phase. If this is a manifestation of the electroclinic effect one would, at first thought, expect it to scale as P ~ (T – TC )−1 and as P ~ E. In reality, however, it scales like P ~(T – TC )−4 and P ~ E 3. In order to find out whether this is consistent with the Landau description of the transition one has to check the precise character of the quantity P actually furnished by the measurement. A recent theoretical model based on the triangle-wave technique combined with the Landau theory for the temperature dependence of the induced polarization in the SmA*-phase is experimentally verified in a number of different compounds. Measurements with the bridge method also confirm the model, indicating the equivalence of the bridge and triangle-wave techniques. The concept of measured (observed) polarization as distinguished from polarization as order parameter in the Landau theory, is pointed out and their relation discussed.