Second‐order quadrupole shift in the incommensurate structures of Rb2ZnBr4 and Rb2ZnCl4

The angular dependences of second‐order 87Rb (1/2 → −1/2) shift in the incommensurate phases of Rb2ZnBr4 and Rb2ZnCl4 are interpreted and EFG‐tensors at the special points of the displacement profile are determined. The EFG‐tensor of I‐structure is described in the approach of perturbance theory: Vij{S} = V {S} + ΔV {S} where the EFG‐tensor of the paraelectric phase is taken as zero‐approximation. It is most important that the form of “modulation correction” tensor ΔVij is not arbitrary. The symmetry properties of one‐dimensional incommensurate modulated atomic chain determine the selection rule for the non‐zero components of the tensor of modulation corrections. The existence of supersymmetry for structurally incommensurate systems follows from the presented NMR‐experiments. The abstract symmetry conservation law at commensurate‐incommensurate transition seems to be demonstrated in this experiment.