Comparative study of critical behavior in several one-dimensionally modulated incommensurate phases by quadrupolar perturbed NMR

Critical behavior of the one-dimensionally modulated incommensurate phases of Rb 2 ZnCl 4 , Rb 2 ZnBr 4 , (NH 4 ) 2 ZnCl 4 , and BCCD was studied by measuring the temperature dependence of the first order quadrupolar perturbation of the NMR-frequencies of suitable nuclei. In each case, results are in accordance with the non-classical critical exponents predicted by the 3d XY model, thus confirming the universality hypothesis. No deviations from the power laws as reported sometimes in literature and attributed to the influence of phase fluctuations could be observed.