Avtor/Urednik		Kutnjak-Urbanc, B; Žekš, B
Naslov		Phase-excitation spectrum of ferroelectric liquid crystals in an external static electric field
Tip		članek
Vir		Phys rev, E Stat phys plasmas fluids relat
Vol. in št.		Letnik 52, št. 4
Leto izdaje		1995
Obseg		str. 3892-903
Jezik		eng
Abstrakt		The dynamics of the phase of the molecular tilt in the helical ferroelectric liquid crystalline Sm-C phase is studied within the Landau model. We show that a static electric field applied parallel to smectic layers induces a gap in the excitation spectrum of the phase of the tilt at the edge of the Brillouin zone. The gap is shown linearly with the strength of the field up to a critical field beyond which the helical structure finally unwinds. The influence of the phase-excitation dynamics on the dielectric response is investigated in order to resolve the contradiction between experimental findings and previous theoretical results. We find the dielectric strength of an infinitely large system to decrease with the bias field and go to zero at the critical field in accordance with measurements. In order to aquire a better understanding, the properties of a system of a finite length along the helical axis are investigated. It is shown the dielectric strength consists of two parts: one related to the local variations of the phase of the tilt and the other related to the unwinding of the whole helical structure. The former part of the dielectric strength vanishes at the critical field, whereas the latter part diverges. In addition, the relaxation time for the unwinding of the helical structure is found to increase with the length of the system and has a range in real planar samples from minutes to hours. In conclusion, the dynamics of the tilt in a finite-size system is found to be crucial in interpreting experimental as well as theoretical results.
Deskriptorji		PHYSICS SPECTRUM ANALYSIS MODELS, THEORETICAL