The results of high-resolution synchrotron x-ray-scattering experiments on the normal-incommensurate phase transition in Rb2ZnCl4 are reported. Measured critical exponents for the intensities of the first three harmonics of the incommensurate modulation wave below T-c agree well with theoretical predictions for the n=2, D=3 (SD-XY) universality class. The scattering observed above T-c corrresponds to critical fluctuations on two distinct length scales: the critical exponents for the short length scale component of the scattering agree with those expected for the 3D-XY universality class. The value found for the exponent of the inverse correlation length of the long length scale component is nu(s)=0.7+/-0.2. A comparison of data taken in Laue and Bragg geometries at different photon energies suggests that the second length scale scattering originates in the near-surface region. Possible explanations of the two length scale behavior are discussed.
Zinkin, M. P., McMorrow, D. F., Hill, J. P., Cowley, R. A., Lussier, J. G., Gibaud, A., Grübel, G., & Sutter, C. (1996). Synchrotron x-ray-scattering study of the normal-incommensurate phase transition in Rb2ZnCl4. Physical Review B, 54(5), 3115-3124. https://doi.org/10.1103/PhysRevB.54.3115