Goldstone dielectric properties

Dielectric Properties Goldstone Mode and Soft Mode... 

Like the usual dielectrics, the ferroelectric smectic-C phase possesses contributions to its dielectric permittivity which are based on the deformation of molecular electron shells and the orientation of permanent molecular dipoles. The dielectric properties at low frequencies, however, are dominated by additional contributions, the Goldstone mode and the soft mode [43], which result from the presence of the spontaneous polarization P and the coupling between P and 9. 

The theory of the dielectric properties of chiral smectic liquid crystals is far from complete, particularly with respect to a molecular statistical approach. Simple Landau theory [31 ] gives expressions for the contributions of soft modes (jj g) and Goldstone modes (Xo) to the low frequency permittivity as ... 

In the standard description of the dielectric properties of the chiral tilted smectics worked out by Carlssonet al. [152], four independent modes are predicted. In the smectic C the collective excitations are the soft mode and the Goldstone mode. In the SmA phase the only collective relaxation is the soft mode. Two high frequency modes are connected to noncollective fluctuations of the polarization predicted by the theory. These two modes become a single noncollective mode in the smectic A phase. There is no consensus [153] as yet as to whether these polarization modes really exist. Investigations of the temperature dependence of the relaxation frequency for the rotation around the long axis show that it is a single Cole-Cole relaxation on both sides of the phase transition between smectic A and smectic C [154]. The distribution parameter a of the Cole-Cole function is temperature-dependent and increases linearly (a=a-pT+bj) with temperature. The proportionality constant uj increases abruptly at the smectic A to SmC transition. This fact points to the complexity of the relaxations in the smectic C phase. 

The response time is dependent on the relaxation time (tg) and dielectric relaxation intensity (Asq) of the Goldstone mode. This demonstrates that a shorter response time would be obtained for the FLCP which possesses strong relaxation intensity of the Goldstone mode at a high frequency range. This confirms that the doping effect of DOS on the electro-optical properties was more pronounced than that of HMAB. 

Levstik A, Carlsson T, Filipic C, Levstik I, Zeks B (1987) Goldstone and soft mode at the smectic-A-smectic-C phase transition studied by dielectric relaxation. Phys Rev A 35 3527-3534 Li J, Wang Z, Cai Y, Huang X (1998) Study of EO properties of polymer network stabilized of ferroelectric hquid crystal in smectic C phase. Ferroelectrics 213 91-98 Li J, Zhu X, Xuan L, Huang X (2002) V-shaped electro-optic characteristics in ELC gels. Ferroelectrics 277 85-105... 

Experimentally the Goldstone and soft modes exhibit properties that are unusual for dielectric process." Although both can be always well... 

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