Charge-density-wave magnetodynamics in NbSe3

We report complex ac conductivity measurements of the charge-density-wave (CDW) conductor Nb${\mathrm{Se}}_3$ in applied magnetic ($H$) fields to 75 kG. Increasing $H$ results in an increase in the characteristic crossover frequency, and an apparent increase in the CDW carrier concentration. A corresponding decrease in the dc threshold field $E_T$ with increasing $H$ suggests a breakdown of the conventional impurity-pinning mechanism in intense magnetic fields.