Seminar QuantAlps Quantum Materials: Thursday, 5th March 2026 at 14:00
Dalila Bounoua (LLB)
Title: Polarized Neutrons Reveal Altermagnetism in MnF2
Institut Néel, Room K223 (Salle Rémy Lemaire)
Abstract: Altermagnets constitute a recently identified class of collinear, magnetically compensated materials in which oppositely oriented magnetic sublattices cannot be mapped onto each other another by a primitive lattice translation or inversion operation. Unlike conventional antiferromagnets, altermagnets break time-reversal symmetry. These distinctive symmetry properties give rise to spin-split electronic bands and chirality-split magnon branches, both exhibiting characteristic anisotropic patterns in momentum space, even in the absence of relativistic spin-orbit coupling [1].
Experimental evidence for spin-split electronic bands has been reported in materials such as MnTe and CrSb using angle-resolved photoemission spectroscopy (ARPES) [2,3], while resonant inelastic X-ray scattering (RIXS) has revealed chiral magnon excitations in CrSb [4]. Polarized neutron scattering, however, provides a unique probe of altermagnetism, as it enables a direct characterization of spin-wave excitations and allows both split magnons [5-7] and their associated chirality [8-10] to be measured simultaneously.
In this work, we investigated the chirality-split magnon spectrum of MnF₂ [9] using polarized inelastic neutron scattering (INS). Our measurements reveal, for the first time in MnF₂, a small but clearly resolvable splitting of the magnon branches, primarily driven by long-range dipolar interactions. Polarization analysis on a magnetically domain-biased sample further uncovers a finite chiral contribution to the neutron scattering cross section, which reverses sign between the two split magnon modes. These observations provide direct spectroscopic evidence of altermagnetism in MnF₂.
[1] G. L. Smejkal et al., Phys. Rev. X 12, 040501 (2022).
[2] J. Krempasky, et al., Nature 626, 517–522 (2024).
[3] S. Reimers et al., Nat. Comm 15, 2116 (2024), G. Yang et al. Nat Commun 16, 1442 (2025).
[4] N. Biniskos et al., Nat Commun 16, 9311 (2025).
[5] Z. Liu Phys. Rev. Lett. 133, 156702 (2024).
[6] Q. Sun et al., Phys. Rev. Lett. 135, 18 (2025).
[7] A. K. Singh et al., arXiv:2511.16086.
[8] P. A. McClarty et al., Phys. Rev. B 111, L060405 (2025).
[9] Q. Faure at al., arXiv:2509.07087 (under review).
[10] J. Sears et al., arXiv:2601.04303v1
