Experimental evidence of soft mode in the smectic C*α phase of chiral ferroelectric liquid crystals

Abstract

Dielectric properties of chiral smectic liquid crystals characterised by the occurrence of the C(α)(*) phase were investigated in the frequency range 10 Hz-1 MHz. In the range of existence of this phase the observed relaxation spectrum is composed of two kinds of mode, and not of a single one, as commonly thought. Phase modes of the Goldstone type coexist in it with an amplitude type soft mode. The share of the soft mode in the global value of electric permittivity ε can be dominant and attain 90%. A possible explanation for that effect is sought in the similarity to chiral phases of the de Vries type.

Complex temperature dependence of the dielectric response in simple SmC* phases

“…Dynamic properties of chiral ferroelectric liquid crystals are usually studied by dielectric means, as in ref. 4–8 and many others. Additionally, a theoretical analysis of a dielectric response close to the SmA*↔SmC* phase transition was used as a standard in other polar liquid crystals as well.…”

“…If one allows for the polarisation to change independently of the tilt, the dynamics becomes more complicated, but the results are consistent with experimental observations such as those found in ref. 8.…”