Author(s): Hanchen Wang, Junfeng Hu, Wenjie Song, Artim L. Bassant, Jinlong Wang, Haishen Peng, Emir Karadža, Paul Noël, William Legrand, Richard Schlitz, Jilei Chen, Song Liu, Dapeng Yu, Jean-Philippe Ansermet, Rembert A. Duine, Pietro Gambardella, and Haiming Yu We report direct spectroscopic evidence of antimagnons, i.e., negative-energy spin waves identified by their signature inverted dispersion and left-handed precession with Brillouin light scattering (BLS) spectroscopy. We investigate an ultrathin BiYIG film with a perpendicular magnetic anisotropy th… [Phys. Rev. Lett. 137, 126703] Published Wed Sep 16, 2026