Collective modes, ferroelectrics

Matsui H, Tsuchiya H, Suzuki T, Negishi E, Toyota N (2003) Relaxor ferroelectric behavior and collective modes in the 7t-d correlated anomalous metal )l-(BEDT-TSF)2FeCl4. Phys Rev 668 155105/1-10... 

The presence of clusters in BC nematics is now well established from various measmements. Recent studies " have in fact indicated a ferroelectric or an antiferroelectric response to an applied electric field, and an unusual low-frequency (presumably collective) mode has been detected in the dielectric spectra of bent-core nematics, which might also be related to clusters. In spite of the intense studies, however, the exact structure and the physical properties of the clusters are still unknown. Therefore, not surprisingly, a precise physical model for the role of polar clusters in the flexoelectric response of BC nematics and a quantitative estimation of the resulting increment of the flexocoefiicients has not yet been worked out. 

Main quantities characterizing the properties of FLCs (the values of the tilt angle d, the spontaneous polarization P, the dielectric constant , the critical frequencies for particular collective modes) depend on intermolecular interactions caused by the chirality of molecules. " Thus the ferroelectricity of LCs must be sensitive to the intermolecular distance it must then be pressure dependent. The pressure studies of FLCs have been undertaken in a few labora-tories. - ... 

Nevertheless, several authors, in studying SmC polyacrylates [22] or SmC poly-siloxanes [ 14,41,67], have observed the two expected collective relaxations in ferroelectric liquid crystals, namely the Goldstone mode and the soft mode. These two relaxations occur at frequencies lower than 10 Hz. 

Hiraoka K, Toyoda S, Houiai Y, Tokita M, Watanabe J (2010) Influence of DC electric field on soft mode of main-chain ferroelectric liquid-crystalline polyesters polymeric effect on collective fluctuation. Appl Phys Express 3(1). doi 10.1143/APEX.3.011701... 

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