Electric-field depinning of charge-density waves in NbSe3

Measurements of the nonlinear conductivity in Nb${\mathrm{Se}}_3$ resulting from the high-temperature charge-density wave (CDW) have been made. The results show that the electronic properties of Nb${\mathrm{Se}}_3$ in the temperature regime where only one CDW exists are qualitatively the same as those in the the region where two CDW's coexist. In both cases a threshold field for non-Ohmic conduction and quasiperiodic noise are observed. These results rule out mechanisms for noise production which rely on the coexistence of two CDW's, such as beat phenomena. Measurements of the temperature dependence of the two threshold fields show a separate depinning of each of the two CDW's at temperatures below 59 K. No evidence for a lock-in of the two threshold fields to a common value has been seen.