Interference Effects of the Charge-Density-Wave Motion in NbSe3

It is reported that steps are induced in the nonlinear $V\left(I\right)\mathrm{}$ characteristic of Nb${\mathrm{Se}}_3$ by a superposed rf current. The frequencies responsible for these steps are interpreted as the Fourier spectrum of the motion of the charge-density wave in an anharmonic potential created by the impurities. It is shown that the relation $\overline{J}=n\mathrm{ev}$ is verified for the excess current $\overline{J}$ carried by the charge-density wave, $v$ being the velocity of the wave. The number of condensed electrons $n$ below the charge-density wave at 59 K is found to be in good agreement with previous measurements.