Size effects and charge-density-wave pinning inNbSe3

We report measurements of the impurity-concentration and crystal-size dependences of the threshold field $E_T$ for charge-density-wave (CDW) depinning in ${\mathrm{NbSe}}_3$. These measurements establish that CDW’s in Ta-doped ${\mathrm{NbSe}}_3$ are weakly pinned. Size dependence of $E_T$ occurs when the transverse crystal dimensions become comparable to the transverse CDW phase-phase correlation length, resulting in a crossover from 3D to 2D weak pinning. A divergence of the T=4.2-K Ohmic resistance with decreasing sample thickness is attributed to diffuse scattering by crystal surfaces.