Spin-group symmetry in magnetic materials with negligible spin-orbit coupling

Understand

Symmetry formulated by group theory plays an essential role with respect to the laws of nature, from fundamental particles to condensed matter systems.

• Here, by combining symmetry analysis and tight-binding model calculations, we elucidate that the crystallographic symmetries of a vast number of magnetic materials with light elements, in which the neglect of relativistic spin-orbit coupling (SOC) is an appropriate approximation, are considerably larger than the conventional magnetic groups.
• Thus, a symmetry description that involves partially-decoupled spin and spatial rotations, dubbed as spin group, is required.
• Spin group permits more symmetry operations and thus more energy degeneracies that are disallowed by the magnetic groups.