Harmonic and direct ac mixing properties of the Fukuyama-Lee-Rice model and the incommensurate chain are determined and compared with experimental data. Field and frequency dependences of both the amplitudes and phases of both of these responses are examined. Agreement with experiment is generally good. For example, classical models can yield low harmonic-mixing quadrature components simultaneously with substantial frequency dependence in both components of the linear response.

• Received 13 November 1986

DOI:https://doi.org/10.1103/PhysRevB.35.7745