Linear and nonlinear ac response of (Ta 1− xNb xSe 4) 2 I alloys

Abstract

We have measured the linear and nonlinear ac response of (Ta 1− x Nb x Se 4) 2 I alloys in the microwave and millimeter wave spectral range. The magnitude, temperature and concentration dependence of the effective mass m ∗ is well described in terms of the mean-field description of the dynamical CDW response. The pinning frequency ω o increases with increasing impurity concentration x, and the concentration dependence is suggestive of strong impurity pinning. Our phase-resolved microwave harmonic mixing (PREHM) experiments are only in semiquantitative agreement with available models.