Measurement of the charge-density-wave correlation length inNbSe3by high-resolution x-ray scattering

We have measured the correlation length of the ${\mathbf{q}}_1$ charge-density wave in ${\mathrm{NbSe}}_3$ using high-resolution x-ray scattering. For a heavily Ta-doped crystal having a residual resistivity ratio ${\mathit{r}}_{\mathit{R}}$ of 10, the T=77 K correlation lengths parallel and transverse to the quasi-one-dimensional ${\mathbf{b}}^{\mathrm{*}}$ direction are ${\mathit{l}}_{\mathit{b}}^{\mathrm{*}}$≊0.9 μm and ${\mathit{l}}_{\mathit{a}}^{\mathrm{*}}$≊0.1 μm, respectively. For an undoped crystal (${\mathit{r}}_{\mathit{R}}$≊300), we obtain lower bounds ${\mathit{l}}_{\mathit{b}}^{\mathrm{*}}$≊2.5 μm and ${\mathit{l}}_{\mathit{a}}^{\mathrm{*}}$≊1.9 μm, the latter value being comparable to the thickness of typical crystals. These results are in excellent agreement with a recent weak-impurity-pinning analysis of finite-size effects observed in transport properties.