The sliding of the room-temperature charge density wave (CDW) in the monoclinic phase of $\mathrm{Nb}{\mathrm{S}}_3$ under rf power is studied. The threshold field, $E_{\mathrm{t}}$, and Shapiro steps’ width, δE, show aperiodic Bessel-type oscillations as a function of rf voltage. Here we demonstrate experimentally that, if presented as a function of CDW path length in each half period of the rf voltage, $E_{\mathrm{t}}$ and δE show periodic oscillations, the period being equal to the CDW wavelength. The result is found to be universal for different compounds and gives clear understanding of the synchronization effects in terms of forced oscillations of a particle in a periodic potential.

• Received 1 November 2019
• Revised 11 February 2020
• Accepted 24 February 2020

DOI:https://doi.org/10.1103/PhysRevB.101.115425