Emerging research landscape of altermagnetism (2204.10844v1)

Abstract: Magnetism is one of the largest, most fundamental, and technologically most relevant fields of condensed-matter physics. Traditionally, two basic magnetic phases have been considered -- ferromagnetism and antiferromagnetism. The breaking of the time-reversal symmetry and spin splitting of the electronic states by the magnetization in ferromagnets underpins a range of macroscopic responses in this extensively explored and exploited type of magnets. By comparison, antiferromagnets have vanishing net magnetization. This Perspective reflects on recent observations of materials hosting an intriguing ferromagnetic-antiferromagnetic dichotomy, in which spin-split spectra and macroscopic observables, akin to ferromagnets, are accompanied by antiparallel magnetic order with vanishing magnetization, typical of antiferromagnets. An unconventional non-relativistic symmetry-group formalism offers a resolution of this apparent contradiction by delimiting a third basic magnetic phase, dubbed altermagnetism. Our Perspective starts with an overview of the still emerging unique phenomenology of the phase, and of the wide array of altermagnetic material candidates. In the main part of the article, we illustrate how altermagnetism can enrich our understanding of overarching condensed-matter physics concepts, and have impact on prominent condensed-matter research areas.

• The paper identifies altermagnetism as a novel third magnetic phase that uniquely exhibits spin-split spectra despite zero net magnetization.
• It introduces a non-relativistic symmetry-group formalism to classify magnetic orders, yielding significant results such as room-temperature spin-splitting in materials like RuO₂.
• The work explores potential applications in spintronics and quantum systems, suggesting that altermagnetism could revolutionize electronic, superconducting, and magnonic technologies.

Emerging Research Landscape of Altermagnetism: An Expert Summary

The paper "Emerging Research Landscape of Altermagnetism" by Šmejkal et al. discusses a potentially significant development in the field of condensed-matter physics: the proposition of a new magnetic phase termed "altermagnetism." The researchers systematically explore this third magnetic phase through theoretical formulations and symmetry principles, emphasizing its potential to fundamentally enhance the comprehension of magnetism and its implications for various applications.

Key Contributions and Findings

1. Third Magnetic Phase: The authors identify altermagnetism as distinct from the traditional categories of ferromagnetism and antiferromagnetism. Ferromagnets, characterized by net magnetization with spin-split spectra, differ from antiferromagnets, which exhibit zero net magnetization. Altermagnets, though having zero net magnetization like antiferromagnets, unexpectedly exhibit spin-split spectra typically associated with ferromagnets.
2. Non-relativistic Formalism: A novel non-relativistic symmetry-group formalism is introduced to resolve the dichotomy observed in altermagnets. This approach highlights the co-existence of compensated antiparallel magnetic order with distinct spin-splitting, proposing a robust framework for their classification as a separate magnetic phase.
3. Implications of Altermagnetic Properties: Altermagnets potentially enhance the understanding of key condensed matter physics concepts such as Kramers theorem and Berry phase phenomena. They provide avenues for unconventional Fermi-liquid instabilities and could foster advancements in electronic, magnonic, and spintronic systems. Notably, the authors document significant numerical results, such as room-temperature orders and large spin-splitting in materials like RuO₂.
4. Material Candidates and Predictions: The paper identifies diverse material candidates for exhibiting altermagnetism, from insulators and semiconductors to metals and superconductors. This broadens the material basis considerably compared to traditional magnetic materials, increasing the scope for future investigations.
5. Applications and Future Directions: Altermagnets exhibit potential for impactful technological applications, particularly in spintronics (e.g., giant magnetoresistance and spin-torque devices), ultra-fast optics, neuromorphics, thermoelectrics, and field-effect electronics. Furthermore, the authors speculate on the synergy of altermagnetism with superconductivity, which could open up pathways for novel quantum computing applications and high-temperature superconductivity research.

Theoretical Implications and Outlook

From a theoretical standpoint, the proposition of altermagnets as a new phase extends the understanding of magnetic phenomena in condensed matter systems. This pushes boundaries by introducing a framework that accounts for non-relativistic spin-splittings without net magnetization, challenging pre-existing paradigms and indicating new frontiers in quantum materials research.

Conclusion

This paper establishes a compelling case for altermagnetism as a fundamental and prevalent phase in magnetism that deserves rigorous experimental verification and exploration. Its introduction may reshape aspects of condensed matter physics and facilitate a deeper integration of magnetism into technological innovations. Future efforts will likely focus on validating the predicted properties experimentally and leveraging the distinctive characteristics of altermagnets to pioneer advancements across various fields of applied physics.