Superspace symmetry of Hg_3-δAsF₆

The authors present a study of the symmetries of the incommensurate composite crystal Hg_{3- delta}AsF₆. The crystal is embedded in a four-dimensional space wherein the atoms are represented by lines and its crystallographic symmetry is determined in this superspace. They apply these supersymmetries to explain systematic selection rules found in previous calculations based on a perturbation approach to the incommensurability near the Fermi surface.