Switching and charge-density-wave transport in NbSe₃. III. Dynamical instabilities

Several unusual dynamical instabilities are found in switching charge-density-wave (CDW) conduction. In samples driven by a dc current, large-amplitude 1/f noise and intermittency occur in regions of negative differential resistance. In samples driven by combined dc and low-frequency ac electric fields, we report the first observation of ‘‘ac switching noise.’’ The power spectrum of ac switching noise is broadband and has amplitude as much as 10 dB larger than the broadband noise associated with dc sliding CDW conduction. In samples driven by combined dc and high-frequency ac electric fields, a period-doubling route to chaos and related instabilities are observed when the CDW is mode locked. All instabilities are consistent with the phase-slip picture of switching CDW conduction. Mode locking and associated instabilities in switching CDW’s are analyzed in terms of the sine circle map, the logistic map, and the theory of noisy precursors.