solid state physics

Solid-state physics, the largest branch of condensed matter physics, is the study of rigid matter, or solids. The bulk of solid-state physics theory and research is focused on crystals, largely because the periodicity of atoms in a crystal — its defining characteristic —facilitates mathematical modeling, and also because crystalline materials often have  electrical, magnetic, optical, or mechanical properties that can be exploited for engineering purposes.
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Noun
1. the branch of physics that studies the properties of materials in the solid state: electrical conduction in crystals of semiconductors and metals; superconductivity; photoconductivity
(hypernym) physics, physical science, natural philosophy