Highlights

The discovery of altermagnetism has been included by Science Magazine in the list of the "top science breakthroughs of 2024". This discovery is the only entry from the field of physics on the prestigious list, which is led by advances in HIV medicine and also includes the landing of a space rocket.
Altermagnetism was proposed a couple of ago in a series of articles by Libor Šmejkal, now a group leader at the Max Planck Institute for the Physics of Complex Systems and the Max Planck Institute for the Chemical Physics of Solids, and colleagues from Prague and Mainz. Their initial prediction in 2018 of an unconventional anomalous Hall effect and a complex compensated spin density in direct and momentum space electronic structures paved the way for their systematic spin-symmetry classification in 2021. This classification uncovered altermagnets as a new class of magnets. In altermagnets, not only the spin polarisation but also the spatial orientation of the adjacent magnetic atoms alternates.
In 2024, researchers published experimental observations of altermagnetism in MnTe and CrSb using momentum-space photoemission spectroscopy at large synchrotron facilities. These experiments were guided by the theoretical work of Libor Šmejkal and his collaborators. The cyan beam in the image represents such a photoemission experiment, used to demonstrate altermagnetism.

Further reading:
L. Šmejkal et al., Science Adv. 6, 23 (2020)
I. I. Mazin et al., PNAS 118, 42 (2021)
L. Šmejkal, J. Sinova, and T. Jungwirth, Phys. Rev. X 12, 031042 (2022)
J. Krempaský, L. Šmejkal, S. W. D'Souza, et al., Nature 626, 517 (2024)
S. Reimers et al., Nat. Commun. 15, 2116 (2024)

The ability to replicate is a hallmark of the living world. Organisms can replicate themselves as well as cells, and DNA replication, RNA transcription, and RNA translation to proteins are examples of polymer template copying. Generating a DNA polymer copy with near-identical sequence to the template DNA requires energy consumption which drives the system out-of-equilibrium and generates dissipation. Now, Arthur Genthon and Frank Jülicher of the Max Planck Institute for the Physics of Complex Systems, and Carl Modes and Stephan Grill of the Max Planck Institute of Molecular Cell Biology and Genetics have proposed a statistical physics framework to investigate the conditions necessary for accurate replication. This framework is thermodynamically consistent, as it includes both the fuel-driven templated copy process and a spontaneous assembly process and also their time-reversed pathways. Furthermore, the authors focused on universal features of copying by considering one-step processes in which molecular details are coarse-grained. This minimal setting allows for the identification of a regime of accurate copying, and led to the discovery of a sharp nonequilibrium transition between regimes of accurate and inaccurate copying. This transition occurs at a threshold fuel drive, which indicates the thermodynamic cost of accuracy.

A. Genthon et al., Phys. Rev. Lett. 134, 068402 (2025)

An international team of researchers, including Libor Šmejkal of the Max Planck Institute for the Physics of Complex Systems and the Max Planck Institute for the Chemical Physics of Solids has revealed nanoscale mapping of altermagnetism. The experimental work was led by researchers from Nottingham, who successfully mapped altermagnetic domains in Manganese Telluride. They also demonstrated control of these domains through nanopatterning and the application of magnetic fields.
The experimental mapping of the direction of altermagnetic domains was made possible using x-ray magnetic circular dichroism, i.e., an absorption sensitivity to left- and right-circularly polarized light. Observing x-ray magnetic circular dichroism in altermagnets also serves as confirmation of the unconventional time-reversal symmetry-breaking electronic structure proposed several years ago. The experiment was designed based on earlier predictions by Libor Šmejkal.
The demonstration of large micrometer-sized domains and their manipulation marks an important step toward bringing altermagnets closer to applications in ultrafast, energy-efficient spintronics and nanoelectronics.

O. J. Amin, A. Dal Din et al., Nature 636, 348 (2024)
L. Šmejkal et al., Science Adv. 6, 23 (2020)

"Cacio e pepe" is a traditional recipe from Rome. It consists of tonnarelli noodles served with a cream of cheese, starch-enriched water, and pepper. Despite its simplicity, it is hard to avoid cheese clumps which make the sauce unpleasant. Interestingly, omitting starch leads to huge clumps (the dreaded "mozzarella phase").
Now, in a preprint highlighted by international news outlets including the New York Times, eight Italian physicists, currently or formerly researchers at the Max Planck Institute for the Physics of Complex Systems, have tackled this crucial problem. Using a homemade experimental apparatus, cheese from Italy, and a bit of data analysis, they produced a phase diagram of "cacio e pepe" sauce by varying temperature and starch content systematically and by characterising the "quality" of the sauce by measuring clump sizes. They found that, above a certain threshold, huge mozzarella-like clumps give way to smaller cheese clusters. They have also modelled their observations in terms of a lower critical solution temperature by introducing a minimal theoretical model that frames the observed phase diagram.

See also the article related to this work in the New York Times.

Giacomo Bartolucci, Daniel M. Busiello, Matteo Ciarchi, Alberto Corticelli, Ivan Di Terlizzi, Fabrizio Olmeda, Davide Revignas, and Vincenzo M. Schimmenti, arXiv:2501.00536 (2025)

During development, tissues fold into the functional shapes of organs and organisms. This morphogenesis is driven by a complex interplay of mechanical forces and molecular signalling. While the latter can be visualized by fluorescent tagging, inferring mechanical forces has remained one of the key challenges of biological mechanics. This is especially tricky in curved cell sheets in which these forces have components out of the tissue plane.
Now, Pierre Haas of the Max Planck Institute for the Physics of Complex Systems and Steph Höhn of the University of Cambridge have shown how to combine a mechanical model and laser ablation experiments to infer these forces from the recoil of a cell sheet on ablation, using the process of inversion of the green alga Volvox as a model system. Bending of cell sheets is often driven by what is called cell wedging (constriction of one side of the cells to splay them and hence bend the cell sheet), but this analysis revealed out-of-plane stresses away from those regions where cell wedging bends the tissue of Volvox. In this way, the researchers provide not only an experimental and theoretical framework to quantify out-of-plane stresses during development, but also show how additional cell shape changes can complement classical cell wedging to drive cell sheet folding.

Pierre A. Haas and Steph S. M. H. Höhn, Phys. Rev. E 111, 014420 (2025), highlighted as an Editors' Suggestion

Symmetry plays a crucial role in understanding fundamental phenomena such as conservation laws, the classification of phases of matter, and their transitions. Recently, researchers have been exploring ways to manipulate symmetries in quantum many-body systems with time-dependent driving protocols and, in particular, engineering new symmetries that do not occur naturally. This enriches the toolbox for quantum simulation and computation significantly, and has led to many exciting discoveries of nonequilibrium phases such as discrete time crystals. However, controlling multiple symmetries—especially in a simple and experimentally friendly way—has remained a challenge. Scientists from the Max Planck Institute for the Physics of Complex Systems have now proposed a novel method to engineer hierarchical symmetries by time-dependent protocols.
By controlling carefully how symmetry-indicating observables evolve over time, the researchers showed how to create a sequence of symmetries that emerge one after another, each with distinct properties. The method relies on a recursive construction that minimizes the effects of symmetry-breaking processes hierarchically. This leads to a corresponding sequence of prethermal steady states with controllable lifetimes, each exhibiting a lower symmetry than the preceding one. The scientists illustrate this protocol with several examples, demonstrating how different types of order can emerge through hierarchical symmetry breaking.
This toolbox of hierarchical symmetries opens a new path to stabilizing quantum states and controlling unwanted symmetry-breaking effects, which can be particularly useful in quantum computing and quantum simulation. The construction applies to classical and quantum, fermionic and bosonic, interacting and noninteracting systems. The underlying mechanism generalizes state-of-the-art dynamical decoupling techniques and is implementable on present-day quantum simulation platforms.

Zhanpeng Fu, Roderich Moessner, Hongzheng Zhao, and Marin Bukov, Phys. Rev. X 14, 041070 (2024)

A few years ago, scientists from the Max Planck Institute for the Physics of Complex Systems
[Saalmann et al., Phys. Rev. Lett. 121, 153203 (2018)] predicted theoretically that the chirp of a short intense laser pulse offers the opportunity to control ionization of atoms with very high efficiency. By means of resonant two-photon processes one can switch between excitation and ionization with a contrast of nearly 100%. This mechanism has now been observed with chirped circularly-polarized laser pulses at the free-electron laser (FEL) FERMI in Trieste (Italy). FERMI belongs to the increasingly popular group of seeded FELs that allow accurate control of the characteristics of the short and intense laser pulses generated. In a large collaboration, led by researchers from the Albert-Ludwigs-Universität Freiburg (Germany), photo-electron spectra from Helium atoms for various chirps—that confirm the theoretical predictions—have been measured. These measurements are a crucial step towards coherent-control experiments making use of spectral-phase shaping in the XUV range of the electromagnetic spectrum.

Fabian Richter, Ulf Saalmann et al., Nature 636, 337 (2024)

Libor Šmejkal, group leader at the MPI-PKS jointly with MPI-CPfS, has been awarded the 2025 Walter Schottky Prize by the German Physical Society (DPG) "for his prediction of altermagnetism, a new class of magnetic order with diverse fundamental and application-oriented perspectives".

Libor Šmejkal was the first to demonstrate the phenomenon of altermagnetism. It is a new fundamental magnetic phase exhibiting a spin-polarized d/g/i-wave order in the non-relativistic band structure, thus differing significantly from conventional ferromagnetism and antiferromagnetism. Previously, the understanding of conventional ferromagnets and antiferromagnets was considered very complete, so Šmejkal's discovery came as an unexpected turn in the scientific community.

Libor Šmejkal was educated at Charles University in Prague under the supervision of Tomas Jungwirth and Jairo Sinova (Mainz), where he received his PhD in 2020. Subsequently, he headed an independent research group at Johannes Gutenberg University Mainz and, since 2024, has been the head of an independent research group at the Max Planck Institute for the Physics of Complex Systems in Dresden.

The Walter Schottky Prize is awarded by the German Physical Society (DPG) for outstanding work published within the last two years, preferably in the past year, in the field of solid-state physics by one or more young physicists. The prize consists of a €10,000 award and a certificate.

Living organisms must sense and process information from their surroundings to survive, but they often cannot directly “listen” to external signals. For example, the internal processes of a red blood cell can only access the external world through the cellular membrane, but how well can this membrane transmit such information? And how can information transmission be achieved with a limited energy budget? Giorgio Nicoletti of EPFL Lausanne and Daniel Busiello of the Max Planck Institute for the Physics of Complex Systems have now shown that, by optimising energy and information at the same time, biological systems can tune themselves to harvest maximal information from the environment. These highly efficient strategies require a price in terms of energy consumption, but this price is far outweighed by the information learned about the hidden, external signals. A particularly relevant case study for these results is red blood cells: The authors quantify how much information about the state of the internal cytoskeleton is transmitted into the flickering of their membrane, unraveling a deep connection between healthy cellular conditions, energy dissipation, and information. In particular, the mechanical stress of the cell affects its efficiency in terms of how well information is transmitted, providing novel and fundamental insights into the functioning of biological systems in complex environments.

Giorgio Nicoletti and Daniel Maria Busiello, Phys. Rev. Lett. 133, 158401 (2024)

Selected for a Viewpoint in Physics.

Periodically driven systems have emerged as a useful technique to engineer the properties of quantum systems, and are in the process of being developed into a standard toolbox for quantum simulation. An outstanding challenge that leaves this toolbox incomplete is the manipulation of the states dressed by strong periodic drives. To achieve fast control of nonequilibrium quantum matter, Paul Schindler and Marin Bukov of the Max Planck Institute for the Physics of Complex Systems have now generalised the notion of variational counterdiabatic driving away from equilibrium. The researchers discuss applications to two-level, Floquet band, and interacting periodically driven models.

Paul M. Schindler and Marin Bukov, Phys. Rev. Lett. 133, 123402 (2024)