Using high-resolution x-ray scattering in the presence of an applied current, we report evidence for a dynamical decoupling between the two ${\mathrm{N}\mathrm{b}\mathrm{S}\mathrm{e}}_3$ charge-density waves (CDWs), $Q_1$ ($T_{C1}=145\mathrm{K}$) and $Q_2$ ($T_{C2}=59\mathrm{K}$), coexisting below $T_{C2}$. Simultaneous and oppositely directed shifts of the relevant CDW superlattice spots develop above a threshold current which we identify as the depinning threshold $I_{C1}$ for the more strongly pinned upper CDW $Q_1$ ($I_{C1}\sim 10I_{C2}$). In contrast with shifts induced by current conversion processes, the present effect is not current polarized and is not limited to the current-contact regions. We propose a model which explains this instability through a sliding-induced charge transfer between the two electronic reservoirs corresponding to the $Q_1$ and $Q_2$ CDWs.

• Received 15 April 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.106404