Ferroelectric switching and phase transitions in thin cells of chiral smectic liquid crystals

Ferroelectric smectic C∗ (SmC∗)–smectic A∗ (SmA∗) phase transitions and ferroelectric switching in thin planar cells of chiral liquid crystals (LC) are studied by second harmonic generation (SHG) technique. Electric field and temperature dependences of reflected and transmitted SHG are studied in order to distinguish between non-linear optical response from the sub-surface layer and the bulk of the LC cell. The analysis of the SHG temperature dependences shows a strong surface coupling resulting in the existence of an unswitchable “frozen” sub-surface layer which retains a stable structure under the application of a DC electric field and temperature variations. Critical exponents in the vicinity of the ferroelectric phase transition show a behavior corresponding to the superfluid helium theory.