Anomalous Quasiparticles in a Topological Metallic Ferromagnet

There are long-standing ideas and experiments concerning the emergence of unconventional quasiparticles in strongly interacting Fermi systerms. The most dramatic are the fractional states originally observed for the two-dimensional electron gases in semiconductor heterostructures subjected to perpendicular magnetic fields, and explained shortly thereafter by Laughlin. Others found in zero field are more subtle in the sense that their peculiarity is reflected in scattering rates which rise linearly with the quasiparticle energies; these are the "marginal" fermions first conjectured for the layered cuprates also displaying high temperature superconductivity. Here we describe experiments revealing signatures of both types of anomalous quasiparticles in zero applied field. The material is Fe3Sn2, a ferromagnet kagome metal, with – according to calculations - numerous Weyl nodes near the Fermi level, and a high Curie temperature of ca. 640K. We investigated the anomalous quasiparticles appearing in the compound at low temperatures using microfocused, laser-based angle-resolved photoemission, together with density functional theory.<br/><br/>Refs.<br/>S. A. Ekahana et al., Nature 627, 67-72 (2024)<br/>S. A. Ekahana et al., Mach. Learn.: Sci. Technol. 4 035021, https://doi.org/10.1088/2632- 2153/aced7d (2023).<br/>M. Yao et al. arXiv:1810.01514.