Chiral-Split Magnon in Altermagnetic MnTe

Recently, spin-symmetry classifications identified a third collinear magnetic class, altermagnetism, named after the alternating spin polarizations in both real and reciprocal spaces [1]. The magnets in the class, altermagnets, combine the features of conventional ferromagnets and antiferromagnets; zero net magnetization in the unit cell and spin-splitting electronic bands due to the non-relativistic exchange origin. In addition to the electronic bands, the altermagnetic magnon bands are theoretically predicted to exhibit chiral splitting as well [2]. The linear dispersive chiral magnons in altermagnets reach the THz frequencies near the Brillouin zone center, unveiling the potential for the stray-field-free ultra-fast spintronics [1, 2]. Though recent photoemission spectroscopy experiments provide evidence for the altermagnetic spin-splitting electronic bands [3], the altermagnetic magnon bands have not been observed yet.

In this work, inelastic neutron scattering (INS) experiments were performed on single crystals of the altermagnetic candidate MnTe by using HRC spectrometer at J-PARC. Well-defined magnon excitations were observed at T = 10 K. An unconventional splitting of magnon dispersions is clearly observed in the spectrum. The -wave harmonic symmetry of altermagnetism in MnTe is verified in the constant-energy slice. Both the split dispersions and -wave patterns are well reproduced by the linear spin-wave theory (LSWT) calculation considering a Heisenberg spin Hamiltonian with a pair of alternating exchange interactions. The calculated neutron chiral factor further demonstrates the chiral splitting of the magnon dispersions. Our results confirmed altermagnetism from the perspective of spin excitation and highlighted its non-relativistic exchange origin, establishing a firm foundation for future explorations in this new magnetic ground state. This work is published in Z. Liu et al., Phys. Rev. Lett. 133, 156702 (2024).



[1] L. Šmejkal et al., Phys. Rev. X 12, 031042 (2022). Phys. Rev. X 12, 040501 (2022).

[2] L. Šmejkal et al., Phys. Rev. Lett. 131, 256703 (2023).

[3] J. Krempaský et al., Nature 626, 517 (2024). S. Lee et al., Phys. Rev. Lett. 132, 036702 (2024).