Speaker
Description
Quantum materials exhibit a plethora of novel electric and magnetic orders beyond the textbook examples of ferroelectrics and ferromagnets. These include multiferroics [1], altermagnets [2], and novel forms of chirality [3]. The richness of materials and phenomena is reminiscent of mid-last-century particle physics, when a confounding zoo of "elementary" particles was only systematically understood after the standard model became established.
We have developed a standard model of electric and magnetic order in crystalline solids that provides a physically transparent, unified framework for the multitude of quantum materials [4,5]. Symmetry is its guiding principle. A formal analogy between space inversion and time inversion is used to identify two complementary, comprehensive classifications of crystals, based on five categories of electric and magnetic multipole order (“polarizations”) and five categories of chirality. Jointly, the categories of polarizations and chirality yield a classification of all 122 magnetic crystal classes into 12 types that exhibit distinct physical properties. The 12-type classification also reveals striking correspondences between apparently dissimilar systems.
The standard model has predictive power by relating electric and magnetic multipolar order with the electronic band structure as well as property and response tensors, in the process enabling the absolute quantification of electric and magnetic multipole order [6].
[1] Fiebig et al., The evolution of multiferroics, Nat. Rev. Mater. 1, 16046 (2016)
[2] Smejkal et al., Beyond conventional ferromagnetism and antiferromagnetism, Phys. Rev. X 12, 031042 (2022).
[3] Fecher, Kübler, Felser, Chirality in the solid state, Materials 15, 5812 (2022).
[4] Winkler, Zülicke, Theory of electric, magnetic, and toroidal polarizations in crystalline solids with applications to hexagonal lonsdaleite and cubic diamond, Phys. Rev. B 107, 155201 (2023).
[5] Winkler, Zülicke, Standard model of electromagnetism and chirality in crystals, arXiv:2405.20940 (2024).
[6] Winkler, Zülicke, Gauge-invariant absolute quantification of electric and magnetic multipole densities in crystals, arXiv:2509.17278 (2025).
| Field of Condensed Matter | Quantum Materials |
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