Abstract
We report the observation of the transient voltage response to current pulses in pure, non-stoichiometric and V-doped blue bronzes A0.30MoO3 (A= K, Rb) near threshold for depinning of the charge density wave. The transient response waveforms involve overshoot and sluggish behaviors at the leading edge of the pulse in pure samples, weak sluggish response in non-stoichiometric samples and strong sluggish behavior in V-doped blue bronzes. The time decays of the transient responses obey stretched exponential laws. The characteristic time for the overshoot obeys a power law as a function of the electric field and is divergent as threshold is approached from above, suggesting that depinning can be viewed as a dynamical critical phenomenon. The transient response has also been studied under inhomogeneous conditions when a current pulse is injected in a segment of the sample while a dc current is flowing in a neighboring segment. The different regimes found in the transient response are analyzed in analogy with strain transient and plastic yielding of a crystal and in terms of combined motion of edge and screw charge density wave phase dislocations interacting with impurities.