Effective index of refraction, optical rotation, and circular dichroism in isotropic chiral liquid crystals

This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependance of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric $P$ is much shorter than the wavelength of the light $\lambda$, an approximation which has been made in previous studies of this problem. The theoretical predictions are supported by comparing them with experimental spectra of the optical activity in the BP III phase.Comment: 15 pages and 7 figures. Submitted to PR

Nonlinear Switching in Surface Stabilized Ferroelectric Liquid Crystals

Dynamics of director field switching in the vicinity of the SmA-SmC$^{*}$ phase transition is studied by means of light scattering. The resonance dependence of scattered intensity on the electric field frequency is observed. The resonance scattering disappears at lower temperatures. The observed anomaly is consistently explained in the framework of the nonlinear kink switching model. The results of this work demonstrate that in the case of materials with high spontaneous polarization this mechanism is predominant

Modulated Structures of the Smectic-C Phase in Free-Standing Films withHigh Spontaneous Polarization

PHYS. REV.

Anomalous multi-order Raman scattering in LaMnO3: a signature of quantum lattice effects in a Jahn-Teller crystal

The multi-order Raman scattering is studied up to a fourth order for a detwinned LaMnO3 crystal. Based on a comprehensive data analysis of the polarisation-dependent Raman spectra, we show that the anomalous features in the multi-order scattering could be the sidebands on the low-energy mode at about 25 cm−1. We suggest that this low-energy mode stems from the tunneling transition between the potential energy minima arising near the Jahn-Teller Mn3+ ion due to the lattice anharmonicity, and the multi-order scattering is activated by this low-energy electronic motion. The sidebands are dominated by the oxygen contribution to the phonon density-of-states, however, there is an admixture of an additional component, which may arise from coupling between the low-energy electronic motion and the vibrational modes. We suggest that superexchange interaction may be crucial in driving the system to the regime of the dynamic Jahn-Teller effect, with affordable barriers for the tunneling between the potential energy minima