We have studied the structure of the ${\mathit{Q}}_1$ charge-density wave (CDW) in pure and Ta-doped ${\mathrm{NbSe}}_3$ as a function of temperature using high-resolution x-ray scattering. The CDW’s phase-phase correlation lengths are much greater than the impurity spacing, and in pure crystals can be comparable to typical sample thicknesses. The corrections decay exponentially in all directions. In a heavily Ta-doped crystal, transverse correlation lengths vary with temperature as the square of the CDW gap. These experimental results agree with the weak-pinning model of Fukuyama, Lee, and Rice, and with the weak-pinning interpretation of previous transport measurements.

• Received 28 December 1993

DOI:https://doi.org/10.1103/PhysRevB.50.8288