Spontaneous phase slippage and charge density wave synchronization near the Peierls transition

The voltage dependences of conductivity, $\ensuremath{\sigma}(V)$, of the monoclinic phase of ${\mathrm{NbS}}_{3}$ are reported. The extremely high coherence of the room-temperature charge density wave (CDW) allows its synchronization by a rf field up to ${T}_{\mathrm{P}1}\ensuremath{\approx}365\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the temperature of the Peierls transition, and above it by about 10 K. The ratio of nonlinear current, ${I}_{\mathrm{nl}}=I\ensuremath{-}V\ensuremath{\sigma}(0)$, to the fundamental frequency of the CDW sliding, ${f}_{\mathrm{f}}$, falls as T increases across ${T}_{\mathrm{P}1}$. This result is considered in terms of spontaneous phase slippage near ${T}_{\mathrm{P}1}$, which could give both single-particle and collective contributions to linear conductivity. The two contributions are considered, and the former is found to dominate. The temperature-frequency dependence of ${I}_{\mathrm{nl}}/{f}_{f}$ is consistent with the model of thermally activated phase slippage.