Specific Features of Light Scattering in [N(CH3)4]2CuCl4 Crystals with an Incommensurable Phase

We present the results of investigation of the optical birefringence and intensity of the main light beam that passed through an [N(CH₃)₄]₂CuCl₄ crystal under the conditions of viscous interaction of the incommensurable structure with defects. A nonmonotonic temperature dependence of the basic signal is revealed. The observed temperature dependence of the intensity (in the form of irregular steps) is related to different periods of the incommensurable structure. In transitions between adjacent metastable states the periodicity of the incommensurable structure changes. It is shown that in transition regions for the central beam one observes an anomalous decrease in the light intensity due to the appearance of a perturbation lattice with the wave vector q.