Dynamics of the electroreflective response of TaS₃

We have observed a large (∼1%) change in infrared reflectance of the charge-density-wave (CDW) conductor, orthorhombic TaS₃, when its CDW is depinned. The change is concentrated near one current contact. Assuming that the change in reflectance is proportional to the degree of CDW polarization, we have studied the dynamics of CDW repolarization through position-dependent measurements of the variation of the electroreflectance with the frequency of square-wave voltages applied to the sample, and have found that the response could be characterized as a damped harmonic oscillator with a distribution of relaxation (i.e., damping) times. The average relaxation time, which increases away from the contacts, varies with applied voltage as τ₀α 1/V^P with p ∼ 3/2, but the distribution of times broadens as the voltage approaches the depinning threshold. Very low resonant frequencies (∼1 kHz) indicate a surprisingly large amount of inertia, which is observable in the time dependence of the change in reflectance as a polarity-dependent delay of ∼100 μs.