Optical signatures of noncentrosymmetric structural distortion in altermagnetic MnTe

Abstract: The hexagonal MnTe is a prime material candidate for altermagnets, an emerging class of magnetic compounds characterized by the nontrivial interplay of antiparallel spin arrangements with their underlying crystal structures. Recognizing precise knowledge of crystal symmetry as the cornerstone of the spin-group classification scheme, we report here a native inversion-symmetry-breaking structural distortion in this compound that has previously been overlooked. Through optical polarimetry experiments and first-principle calculations, we show that MnTe belongs to the noncentrosymmetric $D_{3h}$ group, effectively resolving key inconsistencies in the earlier interpretations of Raman spectroscopy data. Our finding impacts the symmetry analysis of MnTe within the altermagnetic class and sheds light on the mechanism of its magneto-controllable N\'eel order.