Chiral magnons and 'plaid' splitting in the altermagnet MnTe2 ✛ ✦
Context
Altermagnets are a recently discovered class of magnetic materials that combine compensated antiferromagnetic order with band spin splitting, usually typical of ferromagnets. This unique combination arises from special crystal symmetry operations (rotations or reflections) that connect oppositely oriented magnetic sublattices, without spin-orbit coupling. This phenomenon is a direct consequence of Noether's theorem, which links system symmetries to conservation laws. A promising feature of altermagnets is chiral magnons, for which the degeneracy between left- and right-polarized spin waves is lifted, leading to directional propagation asymmetry. Experimental confirmation of such excitations in noncoplanar antiferromagnets remained a challenge until this study on MnTe2.
Methods
To detect magnon chirality, scientists combined Raman spectroscopy with circular polarization control (ellipsometry) and first-principles calculations. MnTe2 single crystals were grown by chemical vapor transport. Raman spectra were recorded at temperatures from 10 to 305 K using a 515 nm laser and superachromatic wave plates to select RL (right-left) and LR (left-right) configurations. In parallel, DFT+U calculations, based on Schrödinger equation, were performed including Coulomb correlations (Ueff = 4.2 eV), and an effective spin Hamiltonian was constructed, including Heisenberg exchange interactions (Werner Heisenberg), Dzyaloshinskii-Moriya vectors, and anisotropic exchange. The magnon spectrum was obtained within linear spin-wave theory (Lev Landau) by diagonalizing the bosonic Hamiltonian using the Colpa method.
Results
The key result is the discovery of a chiral anomaly for the magnon at 2.5 meV. In crossed circular polarizations, the scattering intensity differed between RL and LR, and the sign of the imbalance reversed when switching from Stokes to anti-Stokes components. Normally, the anti-Stokes signal is suppressed due to thermal distribution, but here it is anomalously enhanced. This effect is quantified in the circular Raman dichroism (RCD) spectrum, which shows a sharp contrast specifically for the lower magnon branch. The high-energy magnon at 3.6 meV, on the other hand, showed no noticeable chirality. The angular dependence of the intensity upon rotating linear polarization revealed a symmetry lowering: instead of the expected fourfold symmetry corresponding to the cubic lattice, the magnons exhibited a twofold modulation, along with a 90° rotation of the pattern between Stokes and anti-Stokes parts. Numerical simulation confirmed that the three upper magnon bands near the Γ-point form a 'plaid' texture of spin polarization in k-space—an analog of altermagnetic electron splitting, where the spin projection changes sign with momentum direction. This explains the observed polarization asymmetry: for a given wave vector, one chirality is energetically favored over the other, which corresponds to a superposition of states with different circularity.
Implications
The work proves that noncoplanar antiferromagnets like MnTe2 can serve as a fully-fledged platform for studying altermagnetism, where chiral magnons are not a consequence of relativistic effects but arise from combined spin-lattice symmetry operations. This expands the class of materials for nonreciprocal magnonics. The proposed approach—polarization-resolved Raman spectroscopy—turns out to be a much more accessible method for characterizing altermagnets compared to neutron scattering or photoemission, especially for small samples, and allows direct probing of the chirality of elementary excitations.
Future development
In the future, similar experiments may be extended to other multi-sublattice magnets with nontrivial topology of spin textures. A theoretical description in terms of spin space groups will pave the way for designing materials with desired chiral properties for targeted control of magnon propagation. Integration with quantum optics methods may enable tunable frequency filters and diodes for spin waves.
Impact
The results will impact spintronics (through directional transmission of spin signals), magnonics (microwave devices for quantum information processing), and the fundamental physics of quantum magnets.
Next steps
Next steps include measuring the dispersion of chiral magnons by inelastic neutron scattering and searching for analogous effects in electrically controlled MnTe2 thin films.
Key open problems
The study addresses the problem of achieving nonreciprocal spin transport in magnets without an external magnetic field, which is directly linked to one of the fundamental challenges of nonequilibrium thermodynamics—controlling energy and information flows in quantum systems, where Pauli exclusion principle dictates the correlation of spin and charge degrees of freedom.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The work experimentally confirms the chirality of magnons in the altermagnet MnTe2 using Raman spectroscopy with circular polarization control and DFT calculations. A chiral anomaly was detected for the 2.5 meV magnon: differences in the intensities of RL and LR in the Stokes and anti-Stokes regions, an anomalously enhanced anti-Stokes signal, and a reduction in symmetry from fourfold to twofold.
Where its strength is
The combination of polarization-resolved Raman spectroscopy and first-principles calculations directly revealed the chiral properties of magnons in an altermagnet, providing an experimental foundation for further studies of spin excitations in this class of materials.
Where it could go next
- It might be interesting to explore the connection between the observed magnon chirality and the possible coexistence of multiple magnetic orders in altermagnets, as discussed in the work on the chameleon altermagnet.based on: Chameleon Altermagnet: Two Games on One Chessboard arXiv:2606.29140
- A related idea is using light to control magnetic states; perhaps chiral magnons in MnTe2 could be sensitive to optical excitation, paving the way for optical control of spin waves.based on: How to Paint a Magnet with Light arXiv:2605.03026
- In our archive, there is a work on how crystal symmetry can distinguish hidden magnetism; this could help in searching for other altermagnets with chiral magnons using symmetry criteria.based on: How to Spot Hidden Magnetism by Symmetry arXiv:2605.27151
Worth trying
- Test whether the chiral anomaly of magnons persists as temperature varies near the magnetic phase transition.
- Investigate the effect of an external magnetic field on the chiral splitting of magnons to identify possible rearrangements of the spin texture.
- Compare experimental Raman spectra with calculations for different magnetic configurations to refine the parameters of the spin Hamiltonian.
Why this may matter
The experimental discovery of chiral magnons in an altermagnet opens up the possibility of using these materials in spintronics and magnonics, where the directional propagation of spin waves could be harnessed for dissipationless information transfer.
Nearby works in our archive
- Magnetic Ripples: How Relativity Plays with Spinssimilarity 0.69
- How to Paint a Magnet with Lightsimilarity 0.67
- Mirror Crystal Splits Electron Highwayssimilarity 0.66
- Altermagnets: The Hidden Dance of Spinssimilarity 0.65
- How to Spot Hidden Magnetism by Symmetrysimilarity 0.65
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The closest work in the archive sits at 0.69 by meaning — the usual level for our corpus.
Original abstract
as written by the authors arXiv:2607.02114
Altermagnets constitute an emerging class of magnetic materials that combine compensated antiferromagnetic order with spin-split excitations arising from crystalline symmetries. Despite strong theoretical interest, their experimental identification remains challenging. Here, we demonstrate that helicity- and angle-resolved Raman scattering measurements reveal reduced rotational symmetries of magnons and a pronounced imbalance between left- and right-circular polarization channels, indicating momentum-dependent magnon handedness. First-principles DFT+$$U$$ calculations combined with linear spin-wave theory uncover a characteristic plaid-like spin-splitting structure in momentum space. The resulting magnon spin textures are dictated by the unconventional sublattice symmetries of MnTe$$_2$$ and closely emulate those of altermagnetic electronic bands. Our work provides evidence of chiral spin-wave excitations unique to this non-coplanar antiferromagnet.
Interestingly, the pyrite structure (FeS2), inherited by MnTe2, is known as 'fool's gold,' and it is inside this crystal lattice that chiral magnons hide, resembling tiny vortices swirling in opposite directions.
Key numbers
- lower magnon energy: 2.5 meV
- upper magnon energy: 3.6 meV
- Néel temperature: 87 K
- lattice constant: 6.90 Å
- intra-sublattice exchange J1: 0.675 meV