Generalized Space Groups from Internal Configuration Spaces

Abstract

We develop a unified construction of generalized space groups for crystals with unconventional internal degrees of freedom. Starting from the full group $G_P$ of allowed internal transformations and the stabilizer $P$ of a reference object, we determine the pointwise and setwise symmetries, $J$ and $K$, of the allowed configuration set. Goursat's lemma then couples the internal quotient $K/J$ to a spatial quotient. The framework includes ordinary, magnetic, spin, and color space groups as special cases. As an example, we consider a dodecahedral object with $P=I\simeq A_5$, for which we obtain the nontrivial pair $T◃O$ with $O/T\simeq {\mathbb{Z}}_2$. The resulting generalized space group hosts a point node with topological charge $|C|=12$.

6 pages, 2 figures