Speaker
Description
Chair: Erich Runge
The replacement of Flash memories by spintronic memories on advanced-node microprocessors has made ferromagnets vital complements of semiconductors in present chip industry. The basic physical principal underpinning spintronic functionalities is the time-reversal symmetry breaking. In ferromagnets, it takes the form of lifted Kramers degeneracy of the Fermi surface into majority-spin and minority-spin electronic states, giving rise to internal magnetization. Since magnetization limits scalability due to associated stray fields, and hinders energeticlly inexpensive transition from GHz to THz operation speeds, a new route of research emerged towards spintronics without magnetization. In the talk we first recall how this route was opened by the realization that spin degeneracy does not necessarily exclude breaking of the time-reversal symmetry in Fermi surfaces of some seemingly ordinary collinear antiferromagnets [1,2]. Apart from spintronic memories with no stray fields and switching times scaled down to picoseconds, these antiferromagnets have recently entered the realm of quantum technologies by enabling a demonstration of a field-free and magnetization-free superconducting diode. Despite the progress, the absence of spin splitting is a major roadblock which is circumvented only at the expense of subtle and complex means of operating these antiferromagnetic devices. Instead of circumventing, we will remove the roadblock in the second part of the talk by presenting experimental demonstrations of altermagnetism and of spintronic devices based on this recently identified distinct form of collinear magnetic order [3-12]. A spin-resolved and angle-resolved photoemssion spectroscopy directly evidences that the electronic band structure of altermagnets breaks the time-reversal symmetry by spin-splitting the electronic states, despite vanishing magnetization. This enables to oparate the magnetization-free altermagnetic devices by analogous means to those used in ferromagnetic spintronics, as already demonstrated in altermagnetic anomalous-Hall or spin-injenction devices.
References
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[11] Jungwirth et al., Nature Phys. 22, 1012 (2026)
[12] Mencos et al., Nature in press, arXiv:2512.17427