New Submission: Revisiting the Raman Mode Assignment in Altermagnetic MnTe.

MnTe is an extensively studied altermagnet, yet only a few Raman scattering experiments have been reported, likely because it was considered trivial. All studies observe a mode near 176–184 cm^-1, commonly assigned to the E_2g phonon—the only Raman-active mode allowed by symmetry in space group 194. However, Wu et al.[1] recently noticed that density functional theory (DFT) calculations place the E_2g mode near 90 cm^-1, an unusually large discrepancy. They further claimed that the 176 cm⁻¹ mode appears only in co-polarized spectra and is absent in cross-polarization, inconsistent with E_2g symmetry. To reconcile this, they proposed that MnTe actually adopts a lower-symmetry structure (space group 187) with an alternating uniform shift of the Mn planes (δ ≈ 0.1% of c), corresponding to a frozen displacement of the B_1g phonon, which makes this otherwise silent mode weakly Raman-active.

This is an appealing scenario, but our calculations show that the induced activity of this mode, proportional to δ², is negligible compared to the E_2g mode, making this explanation unlikely. Moreover, DFT structural relaxation consistently converges to the 194 structure. Instead, we suggest that the observed mode originates from a plasmon excitation of doped holes, whose frequency lies in the same range as the reported peak.

[1] A. Wu, D. Cheng, X. Wang, M. Zeng, C. Liu, and X. Li, arXiv preprint arXiv:2503.17742 (2025).