Electro-optic search for threshold divergence of the CDW diffusion constant in blue bronze

We have used the electro-optic response to search for critical divergence of the charge-density-wave (CDW) diffusion constant in blue bronze at the CDW depinning onset. No divergence is observed, setting (Vcrit/Von-1)<0.06 as a limit for the critical voltage. The measured diffusion constant implies an elastic constant consistent with the measured phason velocity, suggesting that CDW polarization involves gradual, rather than soliton-like, changes in phase.