Pseudo-Goldstone mode in altermagnetic $α$-MnTe: High-field electron spin resonance studies

arXiv:2510.24376v2 Announce Type: replace Abstract: We report multi-frequency electron spin resonance spectroscopy studies of $\alpha$-MnTe in magnetic fields up to $16$ T, applied along the easy anisotropy axis. At temperatures below $T_\mathrm{N} = 310$ K, we observe a single resonance line corresponding to the pseudo-Goldstone mode of the antiferromagnetic resonance (AFMR). This mode exhibits the isotropic behavior with $g_\mathrm{eff}=2.01$, consistent with a complete quench of the orbital angular momenta for Mn$^{2+}$ ions. At low temperatures, the resonance mode is remarkably narrow ($\sim50$ mT for the full width at the half-maximum at $5$ K). The AFMR mode exhibits substantial broadening with increasing temperature, which can be understood in terms of the magnon-magnon scattering