Each new family of twisted materials has repeatedly brought new rules for how electrons move and interact. In the language of theorists, each family offers a different Hamiltonian, the mathematical object that specifies a system’s energies and interactions, and therefore a new kind of quantum simulator. A recent Nature study of so-called M-point twisting illustrated the principle vividly: by changing the starting electronic structure of the constituent layers, researchers accessed fundamentally different models with new symmetries. The implication is that exploring other atomic architectures could uncover quantum states and theoretical models that today’s familiar platforms, built almost entirely around graphene and dichalcogenides, simply cannot reach.

Now an international collaboration spanning more than a dozen institutions has provided both the raw building blocks and a practical guide to that vast search. In two back-to-back papers publishing in Science on September 24, the team presents a sweeping computational survey of the two-dimensional materials universe. The first paper maps the electronic structures and topology of nearly 9,000 two-dimensional entries, regardless of whether they are topological. The second paper identifies more than 1,600 candidates whose electronic properties make them promising for twisting, each offering a different starting point for constructing entirely new kinds of quantum simulators.

The motivation behind the effort is straightforward but profound. Every new family of twisted materials gives researchers a chance to ask a different question about quantum matter, and the field has so far sampled only a handful of the possibilities. B. Andrei Bernevig, a professor of physics at Princeton University and coauthor of both studies, framed the ambition directly: the goal is to move beyond the few platforms currently known and explore the enormous range of physics that other layers and other twist angles could make possible. The two catalogs are designed to turn that open-ended dream into a systematic research program that any laboratory with an internet connection can join.

The first study extends topological quantum chemistry, a theoretical framework that connects a crystal’s chemistry and symmetries to the topology of its electronic states, to nonmagnetic two-dimensional materials. Symmetries are the operations, such as rotations and reflections, that leave a crystal’s atomic pattern unchanged, and they constrain how electronic waves can fit together throughout the crystal. Some electronic patterns carry a special robustness: their topology cannot change without a fundamental alteration of the electronic structure. A quantum spin Hall insulator, for example, can be insulating in its interior while carrying current along its edges through channels protected against certain disturbances. Such states offer a route to studying robust quantum behavior and have motivated a wide range of proposals for new electronic devices.

Working from entries in two computational materials databases, the researchers analyzed 8,872 two-dimensional materials and identified 4,073 with nontrivial topology or an obstructed atomic limit. The latter describes a different kind of unusual electronic organization: in one such class, symmetry constrains the centers of electronic charge to sit away from the atoms themselves. Cutting such a crystal along particular boundaries can then expose distinctive electronic states localized at the surface. Luis Elcoro of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, senior author of one of the studies, explained the philosophy behind the work: the symmetry of a crystal yields rules for how electronic states can be arranged, and the team developed those rules for atomically thin layers and turned them into tools that other researchers can apply across thousands of materials.

Alongside the calculations, the collaboration developed crystallographic tables, analysis programs and a public resource called the Topological 2D Materials Database, which carefully distinguishes experimentally reported structures from purely computational candidates. Crucially, the catalog records electronic band structures, the spectrum of energies available to electrons, for layers both with and without topology. Its nearly 9,000 entries thus form a library of Lego-like building blocks. Two identical layers can be combined into a homobilayer, while two different layers can form a heterobilayer, and adding the freedom to choose their relative twist angle multiplies the possibilities into what the authors describe as an embarrassment of riches. It is precisely this combinatorial explosion that the second paper brings structure to.

The second study is built on the physics of moiré patterns, the large-scale interference patterns that emerge when two fine meshes are overlaid with a slight rotation. Something analogous happens when two atomically thin crystals are stacked and twisted: a moiré superlattice forms that dramatically changes how electrons move through the combined system. In suitable materials, twisting produces narrow electronic bands, in which electrons’ kinetic energy is suppressed and interactions between electrons become especially influential. This regime is fertile ground for superconductivity, magnetism and fractional quantum states, and it offers a controllable way to build quantum simulators, materials that physically enact models of interacting electrons, including models whose behavior remains unknown even to theorists.

Led by Yi Jiang, a Princeton postdoctoral researcher, the second study identifies 61 semimetal candidates and 1,568 insulating candidates whose electronic structures are suited to twisting and admit relatively simple theoretical descriptions. The candidates span hexagonal, square, rectangular and oblique crystal lattices, as well as different patterns of electron motion, so that each starting geometry corresponds to a different physical problem. Twisted square lattices, for instance, could simulate the Hubbard model, the paradigmatic framework central to research on high-temperature superconductivity, while rectangular systems could reveal behavior resembling electrons confined to one-dimensional chains. The team’s earlier M-point twisting study, published in Nature in 2025, showed that a different starting electronic structure produces models with new symmetries and new possibilities for simulating interacting electrons, and the new catalog vastly expands the range of such starting points.

The work also reaches beyond computation into the laboratory. The researchers calculated selected twisted bilayers and found narrow bands in compounds including tin diselenide and hafnium disulfide, and they grew bulk crystals of these compounds along with tin disulfide, gallium telluride and zirconium nitride chloride. Initial sample preparation confirmed that the grown materials can be exfoliated, peeled down layer by layer, to single atomic sheets, a critical practical requirement for assembling twisted devices. Leslie M. Schoop, professor of chemistry and director of the Princeton Center for Complex Materials, emphasized that connecting the catalog to crystal growth and exfoliation provides a practical route from an electronic structure computed on a computer to a real sample in the laboratory. Kin Fai Mak of Cornell University added that some candidates are already crystals that can be grown and peeled to a single layer, giving experiments a concrete starting point for building new twisted structures and testing the physics predicted for them. The catalog classifies candidates purely by their electronic suitability for twisting, so the next step is to assemble the layers into devices and probe their collective behavior, a challenge that coauthor Dmitri K. Efetov of Ludwig Maximilian University of Munich says will involve controlling both twist angle and electron density in each new material.

The shared database, assembled by Princeton physics researcher Nicolas Regnault, who is also affiliated with the Flatiron Institute, the École normale supérieure in Paris and the French National Centre for Scientific Research, is intended as a community resource that lets researchers compare individual layers and select candidates for whichever physics they wish to investigate. The logic of the project is deliberately bidirectional: theorists can start from a known problem about interacting electrons and ask which crystal, which layers and which twist will let them study it, while experiments on the cataloged materials may reveal collective states no one anticipated. As Bernevig concluded, the exciting part is that an experiment can also show researchers something they did not know to ask. The publicly available preprints behind the studies, covering the two-dimensional topological quantum chemistry catalog and the theoretically twistable material database, ensure that the full library of building blocks, from quantum spin Hall insulators to Hubbard-model-ready square lattices, is now open to anyone hunting for the next quantum state of matter.

Subject of Research: Computational catalogs of topological and twistable two-dimensional materials for quantum simulation

Article Title: New catalogs map the quantum possibilities of atomically thin materials

Article References: New catalogs map the quantum possibilities of atomically thin materials. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: twistronics, two-dimensional materials, topological quantum chemistry, moiré patterns, quantum simulators, superconductivity, quantum spin Hall insulators, twisted bilayers, materials database, fractional Chern insulators, crystal growth, narrow bands

The material at the heart of the study is chromium thiophosphate, CrPS4, an air-stable, layered magnetic semiconductor that has become a workhorse of two-dimensional magnetism research. On its own, CrPS4 behaves conventionally depending on thickness: few-layer samples can show ferromagnetic order, while bulk crystals adopt an antiferromagnetic arrangement. Neither of these ground states, however, exhibits the hallmark of altermagnetism, which is a finite splitting between electronic states of opposite spin that does not arise from spin-orbit coupling but instead from the symmetry of the crystal and its magnetic arrangement. The researchers reasoned that if two CrPS4 flakes were stacked with their crystal axes rotated by ninety degrees, the interlayer symmetry would be altered in precisely the way theory predicts should generate an altermagnetic state.

The idea traces back to theoretical work suggesting that twisted magnetic van der Waals bilayers constitute an ideal platform for altermagnetism. In an ordinary antiferromagnet, time-reversal symmetry combined with a lattice translation protects the degeneracy of spin-up and spin-down bands, so the electronic structure shows no net spin splitting. When layers are rotated relative to one another, that combined symmetry operation is broken, and the spin degeneracy is lifted in a momentum-dependent fashion. The result is a material whose spins cancel macroscopically, avoiding the stray fields that plague ferromagnetic devices, yet whose electronic bands are split in a way that can carry spin-polarized currents. For spintronics, this combination is extraordinarily attractive: fast switching, dense packing, and robust spin information without the crosstalk that limits conventional magnetic memory.

To test the prediction, the team fabricated orthogonally twisted CrPS4/CrPS4 homostructures, stacking four-layer flakes rotated by ninety degrees relative to each other. They then interrogated the samples with a battery of optical probes, beginning with polarized Raman spectroscopy. In the twisted configuration, the Raman spectra revealed a splitting of phonon modes that is absent in untwisted controls. This vibrational fingerprint, the researchers show, arises from the interlayer coupling unique to the altermagnetic arrangement: the same symmetry breaking that splits the electronic bands also modifies the lattice dynamics, producing a spectroscopic signature that distinguishes the twisted state from any simple superposition of ferromagnetic and antiferromagnetic layers.

The more decisive evidence came from magneto-optical spectroscopy. Measuring the photoluminescence of the twisted homostructure under an applied magnetic field, the researchers tracked the degree of circular polarization of the emitted light. The twisted sample displayed a magnetic-field dependence that resembles the response of a ferromagnet, a striking result given that the underlying spin order is compensated. Even more telling was the observation of a pronounced Zeeman splitting in the photoluminescence spectra, with the sigma-plus and sigma-minus emission peaks separating as the field increased. Crucially, neither ferromagnetic nor antiferromagnetic CrPS4 samples show this splitting in the same configuration. Its emergence only in the twisted geometry indicates that the stack has entered a genuinely distinct magnetic ground state, one that carries the fingerprints of altermagnetism.

First-principles calculations reinforced the interpretation. Using density functional theory with an on-site Coulomb correction to treat the correlated chromium d electrons, the team computed the electronic structure of the orthogonally twisted bilayer and found large spin-split bands in an antiferromagnetic configuration. The pattern of the splitting matches the theoretical expectations for altermagnets: opposite-spin bands separate in momentum space in a way dictated by crystal rotation symmetry, while the net magnetization remains zero. The agreement between the computed band structure and the optical measurements provides a coherent picture in which twisting acts as a symmetry-breaking knob that switches on spin splitting without introducing any net magnetic moment.

The significance of the result extends beyond confirming a theoretical prediction. Van der Waals homostructures, in which the same material is stacked with controlled twist angles, have already revolutionized research on graphene and transition metal dichalcogenides, giving rise to moiré physics, flat bands, and correlated electronic phases. The present work shows that the same stacking engineering can serve as a design principle for magnetism itself. Rather than searching for new chemical compounds that happen to be altermagnets, researchers can now, in principle, manufacture altermagnetic states from well-characterized magnetic layers by choosing the twist angle. Because the twist angle is a continuously tunable parameter, it opens a route to systematically exploring how altermagnetic spin splitting evolves with interlayer symmetry, something no fixed crystal structure can offer.

The experimental signatures reported here also add to a growing toolbox for identifying altermagnets. Earlier confirmations of altermagnetic band splitting relied on techniques such as spin-resolved and angle-resolved photoemission spectroscopy, x-ray magnetic circular dichroism, and magneto-optical Kerr effect measurements in compounds like CrSb, MnTe, and RuO2. The CrPS4 study demonstrates that circularly polarized photoluminescence and Raman spectroscopy, both accessible table-top optical methods, can detect altermagnetism in atomically thin devices. This accessibility matters: optical probes can be applied to microscopic samples inside cryostats, under magnetic fields, and across device geometries, accelerating the pace at which candidate altermagnetic structures can be screened and characterized.

For applications, the appeal of altermagnets lies in their potential to combine the speed and stability of antiferromagnetic spintronics with the readout convenience of ferromagnets. Antiferromagnetic memory elements are immune to external fields and can in principle switch at terahertz frequencies, but their vanishing net moment makes them hard to read. Altermagnets solve the readout problem because their spin-split bands allow spin-polarized transport and magneto-optical signals even without net magnetization. A twisted van der Waals altermagnet adds another dimension: the state exists in an atomically thin, air-stable semiconductor that can be integrated into heterostructures with other two-dimensional materials, potentially enabling spin filters, tunnel junctions, and valleytronic devices in which spin and momentum are locked by design.

Challenges remain before such devices materialize. The reported signatures are spectroscopic rather than transport-based, and future work will need to demonstrate electrical readout and manipulation of the altermagnetic state, quantify the magnitude and temperature stability of the spin splitting, and explore how different twist angles and layer numbers tune the effect. Still, the demonstration that a simple ninety-degree rotation of identical CrPS4 flakes produces a magnetic phase absent from either constituent marks a conceptual milestone. It establishes twisted van der Waals homostructures as an experimental platform for altermagnetism, transforming a theoretical proposal into a tangible, measurable state of matter and handing the spintronics community a new material class to engineer.

Subject of Research: Experimental observation of altermagnetism in orthogonally twisted CrPS4 van der Waals homostructures

Article Title: Altermagnetism in twisted van der Waals homostructures

Article References: Chen, J., Xie, X., Li, S., Zhang, S., Hou, S., Zhang, X., He, J., Liu, Z., Wang, J.-T., & Liu, Y. (2026). Altermagnetism in twisted van der Waals homostructures. Nature Physics. https://doi.org/10.1038/s41567-026-03440-y

Image Credits: AI Generated

DOI: 10.1038/s41567-026-03440-y

Keywords: altermagnetism, CrPS4, van der Waals heterostructures, twisted bilayers, spintronics, magneto-optical spectroscopy, Zeeman splitting, Raman spectroscopy, 2D magnets, spin splitting, antiferromagnetism, first-principles calculations