Frequency and voltage dependence of the complex shear compliance of A relaxation analysis

We have measured the complex shear compliance of the charge-density-wave (CDW) conductor orthorhombic (Formula presented) for elastic frequencies between 0.1 and 30 Hz, by directly measuring the sample strain (twist angle) for an applied alternating stress (torque). Both the real and imaginary parts of the compliance increase when the CDW is depinned. If the CDW is depinned with an ac current, the elastic anomalies depend on the frequency of the current, as previously observed for the Young’s modulus at higher frequencies. For dc depinning, we have fit the complex compliance to a generalized Debye relaxation expression [S. Havriliak and S. Negami, J. Polym. Sci. C 14, 99 (1966)]. This fit allows us to determine the voltage dependence of the relaxation strength and average relaxation time: (Formula presented) where (Formula presented) is the threshold for CDW depinning.