Chiral Magnonic Anomaly in Magnetic Weyl Semimetal FM-EuCd₂As₂

The interplay between topological band structure and magnetic ordering in magnetic topological phases can exhibit extraordinary physical properties enabling Axion insulator, magnetic Weyl semimetals, and quantum anomalous Hall insulator. The chemical tunability of EuCd₂As₂ materials has two magnetic ordering states: antiferromagnetic (AFM) and ferromagnetic (FM). While AFM-EuCd₂As₂ has an axion insulating state due to its symmetry breaking with spin configuration, FM-EuCd₂As₂ is an ideal candidate for Weyl physics studies because of the minimum number of Weyl points with opposite chirality. We use helictical-resolved Raman spectroscopy to observe phonon modes and signature of chiral magnons with applied magnetic field of a FM-EuCd₂As₂ crystal. We show the behavior of E_g and A_g phonon modes, and their dependence on magnetic ordering below the Curie temperature, at approximately 26 K. We also show that the two magnons peaks at 10.7 and 24 meV at cryogenic temperature move to blue- or red-shifts depending on the circularly polarized excitation with applied magnetic field. The energy shifting increases (1 meV/T at 4.2 K) as temperature decreases under the same field. This energy shifting behavior with each helical direction persists above the Curie temperature. Our results contribute to understanding the topological chirality of FM-EuCd₂As₂ coupled with a helictical light creating chirality imbalance by the magnetic field and allows deeper investigations of Weyl systems for novel applications.