NONLINEAR DIELECTRIC-SPECTROSCOPY OF THE GOLDSTONE MODE IN A FERROELECTRIC LIQUID-CRYSTAL

The nonlinear dielectric spectroscopy of the Goldstone mode has been performed in a ferroelectric liquid crystal. The third-order dielectric constant obtained from the experiments was analyzed in terms of a formula derived from a phenomenological equation of motion by Orihara and Ishibashi [J. Phys. Sec. Jpn. 62 (1993) 489]. The dispersion and the Cole-Cole plot of the third-order dielectric constant were well reproduced by the theory, and the relaxation times obtained from the linear and the third-order dielectric constants were the same, indicating that the equation of motion is still valid in obtaining the nonlinear dielectric constants as well as the linear one. On the basis of the experimental results we discuss dynamic equations described in terms of fractional derivatives.