Evidence for one-half charge-density-wave wavelength pinning periodicity in Peierls conductors

It is shown that, for transition-metal trichalcogenides Nb${\mathrm{Se}}_3$, for Ta${\mathrm{S}}_3$ both with a monoclinic and an orthorhombic unit cell, and for transition-metal tetrachalcogenide ${\left(\mathrm{T}\mathrm{a}{\mathrm{Se}}_4\right)}_2$I, compounds which exhibit transport properties associated with charge-density-wave motion, the linear relationship between the current carried by the charge-density wave and the fundamental frequency of the ac voltage detected in the nonlinear state leads to a pinning potential periodicity which is half the charge-density-wave wavelength in agreement with the recent theory of Josephson oscillations of Barnes and Zawadowski.