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Superstructure (condensed matter)
In solid state physics, a superstructure is some additional structure that is superimposed on a given crystalline structure. A typical and important example is ferromagnetic ordering.
In a wider sense, the term superstructure is applied to polymers and proteins to describe ordering on a length scale larger than that of monomeric segments.
== Superstructure in crystals ==
In a crystal, a superstructure manifests itself through additional reflections in diffraction patterns, e.g., in low energy electron diffraction (LEED) or X-ray diffraction experiments. Often a set of weak diffraction spots appears between the stronger spots belonging to what is referred to as the substructure. In some cases a phase transition occurs, e.g., at higher temperatures, where the superstructure disappears and the material reverts to the simpler substructure. If not, usually compounds are known that exhibit only the substructure.
The superspots basically represent a ''modulation'' of the substructure that causes the translation symmetry inherent to the lattice of the substructure to be violated somewhat. One could speak of symmetry breaking of the translation symmetry of the lattice, although rotational symmetry may be lost simultaneously.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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