Structural studies of the q1 charge-density-wave in NbSe3

X-ray scattering studies of NbSe3 show : i) that the q1 charge density wave (CDW) fluctuations correspond to quasi-two-dimensional correlations with an inplane anisotropy ξb*/ξa* ∼ 3.5. ii) The wave vector q1 has a significant temperature variation accounted for by an activation energy of about 600K. iii) Higher order (n=2,3) harmonics are evidenced. Their temperature variation shows a clear saturation of the intensities at onset temperatures decreasingly smaller when increasing n. The results suggest the presence of an Ising like feature underlying the CDW. (orig.)