Electroclinic effect around a smectic A-chiral nematic phase transition

Abstract

We present measurements of the dynamics of the electroclinic effect around a smectic Achiral nematic transition. The phenomenon has been studied between 1 kHz and 1 MHz, extending by one order of magnitude the frequency range of previous studies. The results have unambiguously allowed us to distinguish two additive mechanisms in the generation of the optical tilt. A model to explain the physical origin of both mechanisms is presented. The first mechanism (fast) is the only bulk process intrinsic to the material and behaves normally at the transition, in the sense that both the magnitude of the tilt as well as the relaxation time have the expected temperature dependence. On the other hand, the second mechanism (slow) is not properly an electroclinic effect, but a surface-mediated effect driven by elastic forces. This explains the apparent anomalous behaviour of the phenomenon reported in the literature one decade ago.