I am fascinated by the potential of altermagnets and odd-parity-wave magnets, as they are highly spin-active yet display no overall magnetic fields. My work involves exploring these unique materials with a vision to develop computing solutions that are denser, faster, and more energy-efficient.

Research interests

• Altermagnetism
• P-wave and odd-parity-wave magnets
• Giant and tunneling magnetoresistance in altermagnets

Invited talks

• “Altermagnets and odd-parity-wave magnets”

Quantum Physics and Technology (qGAP) Seminar, University of Oslo, June 2025

• “Odd-parity-wave magnets”

IEEE Magnetic Frontiers 2025, Liblice, Czech Republic

• “Unconventional p-wave magnets”

ICM 2024, Focus Session on Altermagnetism (major magnetism conference)

• “From altermagnets to p-wave magnets: electronic structure and spintronics applications”

Spins, Waves and Interactions 2024, Greifswald (spintronics workshop)

• “From spin symmetries to magnetoresistance effects in altermagnets”

Spintronics and Quantum transformation 2023, Jülich (EU-Japan workshop)

• “Altermagnetic crystals and spin-polarized transport”

Nanophysics and Nanotechnology seminar organized by Prof. Roland Wiesendanger, University of Hamburg, November 2023

• “Giant magnetoresistance effects in altermagnets”

Seminar in group of Prof. Stefano Sanvito, Trinity College Dublin, May 2023

Education

Ph.D. Computational Condensed Matter Physics, Johannes Gutenberg Univeristy | 2020-2025

• Distinction (Summa cum laude)

M.Sc. Quantum Physics, Niels Bohr Institute, University of Copenhagen | 2017-2019

• Honorary Graduate Award, Frederikke Lørup's Memorial Donation

B.Sc. Physics, University of Oslo | 2014-2017

• Academic Exchange Semester, Nagoya University | 2016

Altermagnetism Q&A

What are altermagnets?

Altermagets are collinear, magnetically compensated magnets that belong to a spin symmetry class (type-III), which means that atoms with opposite spins are related by rotating and/or mirrorring them [1]. The altermagnetic type-III spin symmetry class is completely distinct from that of ferro(ferri-)magnets (type-I) and antiferromagnets (type-II). Consequently, altermagnets have alternating spin polarizations in real and wave-vector space. This combination is not available in neither ferro(ferri-)magnets nor antiferromagnets [1].

What makes altermagnets interesting?

The symmetries of altermagnets dictate that their energy-wavevector dispersions are spin-polarized and spin-split. A combination of nonrelativistic quantum mechanical exchange and crystal fields that are naturally present in the system dictates the size of this spin splitting energy. In other words, the spin splitting in altermagnets is not a relativistic correction, and its size in energy can therefore be orders of magnitude larger than splittings due to spin-orbit coupling. In turn, altermagnets are candidates for hosting many unconventional spintronics effects, such as an unconventional anomalous Hall effect [2], spin currents, and giant and tunneling magnetoresistance [3-5], and this without creating large stray fields like in ferromagnets or requiring large spin orbit-coupling. Moreover, several materials researched in other fields, such as magnetic semiconductors, insulators, and superconductors, also exhibit altermagnetic symmetries [6].

Is there experimental evidence of altermagnetism?

The first description of the altermagnetic electronic band structure in the entire Brillouin zone predicted that altermagnets host time-reversal symmetry broken energy bands and the anomalous (crystal) Hall effect [2]. This effect was measured in several altermagnetic candidates [7-9]. Also, spin currents have been indirectly measured via the torque an altermagnetic candidate exerts on a ferromagnet [10-12]. Such measurements suggests that these systems can be altermagnetic, as the effects are possible due to the specific symmetries of altermagnets. Moreover, time-reversal symmetry breaking of the electronic band structure was observed directly in a material candidate [13]. Most recently, (spin-polarized) ARPES showed the band structure lifts Kramers spin degeneracy altermagnetically [14-19], which is considered direct evidence of altermagnetism. This has created excitement also beyond the scientific community.

[1] Šmejkal, L., Sinova, J., and Jungwirth, T., Phys. Rev. X 12, 031042 (2022). arXiv:2105.05820.
[2] Šmejkal, L., González-Hernández, R., T. Jungwirth, and J. Sinova, Sci. Adv., 6, 23, 6 (2020). arXiv:1901.00445.
[3] Rafael González-Hernández, Libor Šmejkal, Karel Výborný, et al., Phys. Rev. Lett. 126, 127701 (2021).
[4] Šmejkal, L., Hellenes, A. B., González-Hernández, R., Sinova, J., and Jungwirth, T., Phys. Rev. X 12, 011028 (2022). arXiv:2103.12664.
[5] Shao, DF., Zhang, SH., Li, M. et al. Nat Commun 12, 7061 (2021). arXiv:2103.09219.
[6] Šmejkal, L., Sinova, J., and Jungwirth, T., Phys. Rev. X 12, 040501 (2022).
[7] Feng, Z., Zhou, X., et al. Nat Electron 5, 735–743 (2022). arXiv:2002.08712.
[8] Gonzalez Betancourt, R. D., et al. Phys. Rev. Lett. 130, 036702 (2023). arXiv:2112.06805.
[9] Reichlova, H., ..., Hellenes, A. B., et al. Nat Commun 15, 4961 (2024). arXiv:2012.15651.
[10] Bose, A., Schreiber, N.J., Jain, R. et al. Nat Electron 5, 267–274 (2022).
[11] H. Bai, L. Han et al., Phys. Rev. Lett. 128, 197202 (2022).
[12] Karube, S., Tanaka, T., et al., Phys. Rev. Lett. 129, 137201 (2022).
[13] O. Fedchenko, J. Minar, A. Akashdeep, ..., Hellenes, A. B., et al., Sci. Adv 10, eadj4883 (2024).
[14] J. Krempaský, L. Šmejkal, ..., Hellenes, A. B., et al., Altermagnetic lifting of Kramers spin degeneracy. Nature 626, 517–522 (2024). arXiv:2308.10681.
[15] Suyoung Lee, Sangjae Lee, et al., Phys. Rev. Lett. 132, 036702 (2024). arXiv:2308.11180.
[16] T. Osumi, [16] T. Osumi, S. Souma, et al., arXiv:2308.10117.
[17] Reimers, …, Hellenes, A. B., et al. Nat. Commun. 15, 2116 (2024), arXiv:2310.17280.
[18] Ding et al., Phys. Rev. Lett. 133, 206401 (2024), arXiv:2405.12687.
[19] Zeng et al., Adv. Sci. 11, 43, 2406529 (2024), arXiv:2405.12679.

News

Science Magazine recognized altermagnetism as one of the top 10 science breakthroughs of 2024, Dec. 12, 2024.

Science Magazine article wrote about the evolution of the altermagnetism field and the newest spectroscopy experiments on Feb. 6, 2024.

The Economist wrote about altermagnetism and spectroscopic evidence on Jan. 24, 2024.

Organized the PhD focus session at the 2024 German physics society (DPG) meeting in Berlin on the topic "Altermagnets: foundations and experimental evidence". The program is available here.

Gave talk in course "Applied Artificial Intelligence and Innovation" of Dipl.-Math. Jürgen Halt, for business students at the master level at the University of Applied Sciences Ansbach/Germany, June 2023. "How Computing Hardware Meets the Demands of Today's World"

Gave talk in focus session "Altermagnetism: Transport, Optics, Excitations" at the DPG meeting, March 2023.

Poster prize at the European school of magnetism 2022 together with Elena Stetco, who herself won a price for writing the winning nomination. The topic of the poster was altermagnetism and giant magnetoresistance effects with them.

Gave talk in course "Applied Artificial Intelligence and Innovation" of Dipl.-Math. Jürgen Halt, for business students at the master level at the University of Applied Sciences Ansbach/Germany, June 2022. "Antiferromagnetic spintronics"

Selected Publications

See also: Google scholar

arXiv:2309.01607

P-wave magnets. Anna Birk Hellenes, Tomáš Jungwirth, Jairo Sinova, Libor Šmejkal.

Nature

Altermagnetic lifting of Kramers spin degeneracy. J. Krempaský, L. Šmejkal, S.W. D'Souza, M. Hajlaoui, G. Springholz, K. Uhlířová, F. Alarab, P.C. Constantinou, V. Strokov, D. Usanov, W.R. Pudelko, R. González-Hernández, A. Birk Hellenes, Z. Jansa, H. Reichlová, Z. Šobáň, R. D. Gonzalez Betancourt, P. Wadley, J. Sinova, D. Kriegner, J. Minár, J.H. Dil, T. Jungwirth. arXiv:2308.10681

Nature Communications

Direct observation of altermagnetic band splitting in CrSb thin films. Sonka Reimers, Lukas Odenbreit, Libor Smejkal, Vladimir N. Strocov, Procopios Constantinou, Anna Birk Hellenes, Rodrigo Jaeschke Ubiergo, Warlley H. Campos, Venkata K. Bharadwaj, Atasi Chakraborty, Thiboud Denneulin, Wen Shi, Rafal E. Dunin-Borkowski, Suvadip Das, Mathias Kläui, Jairo Sinova, Martin Jourdan.

Science Advances

Observation of time-reversal symmetry breaking in the band structure of altermagnetic RuO2. Olena Fedchenko, Jan Minár, Akashdeep Akashdeep, Sunil Wilfred D’Souza, Dmitry Vasilyev, Olena Tkach, Lukas Odenbreit, Quynh Nguyen, Dmytro Kutnyakhov, Nils Wind, Lukas Wenthaus, Markus Scholz, Kai Rossnagel, Moritz Hoesch, Martin Aeschlimann, Benjamin Stadtmüller, Mathias Kläui, Gerd Schönhense, Tomas Jungwirth, Anna Birk Hellenes, Gerhard Jakob, Libor Šmejkal, Jairo Sinova, Hans-Joachim Elmers (2024).

Physical Review X

Giant and Tunneling Magnetoresistance in Unconventional Collinear Antiferromagnets with Nonrelativistic Spin-Momentum Coupling. Libor Šmejkal, Anna Birk Hellenes, Rafael Gonzáles-Hernández, Jairo Sinova, Tomáš Jungwirth (2022).

Physical Review Letters

Nonlocal conductance spectroscopy of Andreev bound states: Symmetry relations and BCS charges. Jeroen Danon, Anna Birk Hellenes, Esben Bork Hanse, Lucas Casparis, Andrew P. Higginbotham, and Karsten Flensberg (2020).

 

 

My current research focuses on understanding the electronic structure and band-topology of compensated magnets using a combination of density functional theory and symmetry analysis. I am particularly interested in spin transport phenomena originating from compensated magnetic orderings.

Publications:

Physical Review Letters:

• Pari, Nayra A. Álvarez, Daniel Julio Garcia, and Pablo S. Cornaglia. "Quasiparticle mass enhancement as a measure of entanglement in the Kondo problem." Physical Review Letters125.21 (2020): 217601

Research interests:

• Strongly correlated electron systems, quantum entanglement.
• Topological phases of matter, such as Dirac semimetals, Topological insulators.
• First principle calculations, DFT, and post-processing.

Antiferromagnets (AFMs) possess characteristics that make them ideal for spintronic applications: intrinsically, AFM dynamics are much faster compared to FM, AFMs are insensitive to external fields due to their zero net magnetization and produce no stray fields. However, FMs can be manipulated more efficiently. Thus combining AFMs and FMs into hybrid devices to exploit the manipulability of FMs together with the speed of AFMs is a desirable goal. Today, such hybrid devices are widely used, with AFMs having a passive role.

My research is directed to investigate whether AFMs can also be used as active parts in hybrid devices. I am interested in both the static domain wall configurations and domain wall dynamics originating from the combination of an AFM with a FM layer. While using analytical methods to understand the physics and link phenomenology to microscopic theories, I utilize atomistic simulations from ab initio constants and micromagnetic simulations to model larger and more realistic systems that can be compared to experimental data. In a collaboration with the group of Prof. Dr. Nowak at the University of Konstanz I co-develop atomistic spin dynamics simulations. I enjoy working in an interdisciplinary environment in close collaboration with colleagues from both theoretical and experimental physics. On a broader scale I am also interested in scientific applications of machine learning and artificial intelligence.

Research Interests:

 

 

The field of spintronics aims at writing and reading information form materials as we have them in memory drives. Conventionally ferromagnets (FMs) have been used as the materials in devices but they are reaching their limits in size speed and stability. Thus, other materials such as antiferromagnets (AFMs) and the newlly established altermagnets (ALMs) are investigated as a possible substitute.

Both classes show strong coupling between magnetic and elastic degrees of freedom for a variety of materials within. Such coupling allows to manipulate magnetic properties as anisotropy or the magnetic domains of the crystal with strains. Therefore, it is essential to understand the magnetoelastic interactions  to understand and control the behaviour of AFMs and ALMs.

My research is directed to the incluence of the magnetoelastic interaction in AFMs and ALMs from various aspects. I am interested in a range from microscopic phenomena as electronic structure, transport or topology of such crystals under strain as well as macroscopic domain formation and control in the presence of strain gradiets. For this I combine group theory with ab-initio calculations and perform analytics with phenomenological micromagnetic models.

 

Publications

Domain-wall orientation in antiferromagnets controlled by magnetoelastic effects (Preprint)

 

Master Thesis

Antiferromagnetic domains in the presence of magneoelastic interactions

 

Bachelor Thesis

Modelling of the magnetic states and phase transitions in Hematite