The TRR 227 kindly invites you to the joint Colloquium of the TRR 227 & the Dahlem Center for Complex Quantum Systems.

Speaker: Dr. Libor Šmejkal (Max Planck Institute for the Physics of Complex Systems, Dresden)

Title: Altermagnetism: From spin crystallography to nanoelectronics

Abstract:

Recently discovered unconventional magnets extend beyond traditional ferromagnets and antiferromagnets, opening research directions in nanoelectronics and quantum materials. In particular, they promise orders-of-magnitude improvements in the speed and energy efficiency of magnetic memory for artificial intelligence. A defining feature is electron spin splittings on the electron-volt scale without net magnetization.

In this talk, we introduce spin group crystallography as a framework that systematically classifies magnetic order through the interplay of spin and lattice symmetries. Using this approach, we identify two previously overlooked magnetic phases. Altermagnets exhibit collinear but spatially alternating spin arrangements, resulting in strongly direction-dependent spin-polarized electronic states. Antialtermagnets, by contrast, generate momentum-dependent spin polarization, where electrons moving in opposite directions carry opposite spins.

We present key experimental evidence, including spin-resolved photoemission spectroscopy, that confirms these predictions and establishes these phases as fundamental complements to conventional magnetic orders. Finally, we highlight emerging functionalities in spintronics and nanoelectronics, including spin-based memory and multiferroic effects enabled by spin crystallography. These results establish spin crystallography as a predictive framework for discovering and designing functional quantum materials.

References

[1] L. Šmejkal, R. González-Hernández, T. Jungwirth and J. Sinova, Sci. Adv. 6 (23), eaaz8809 (2020).
[2] I.I. Mazin, K. Koepernik, M.D. Johannes, R. González-Hernández, and L. Šmejkal, PNAS 118, 42 (2021).
[3] L. Šmejkal, Jairo Sinova, T. Jungwirth, Phys. Rev. X 12, 031042 (2022).
[4] J. Krempaský, L. Šmejkal, S.W. D'Souza et al. Nature 626, 517 (2024).
[5] T. Jungwirth, J. Sinova, R.M. Fernandes, Q. Liu, H. Watanabe, S. Murakami, S. Nakatsuji, and L. Šmejkal, Nature 649, 837 (2026).
[6] J. Mitscherling, J. Priessnitz, C.K. Geschner, and L. Šmejkal, arXiv:2603.09736 (2026).
[7] J. Priessnitz, A.B. Hellenes, R. Comin, and L. Šmejkal, arXiv:2603.19107 (2026).