Electronic structure and topology across T_c in the magnetic Weyl semimetal Co₃Sn₂S₂

Half-metallic ferromagnet Co₃Sn₂S₂ was recently predicted and experimentally confirmed to host topological Weyl points just above the Fermi energy. Using a combination of tight binding models and first principles calculations, we present an analysis of the electronic structure and magnetism in this material. We argue that Co₃Sn₂S₂ evolves from a Mott ferromagnet below the Curie temperature (T_c = 177K) to a correlated metallic state above T_c. We show how the magnetism in Co₃Sn₂S₂ can be represented using a tight-binding model consisting of Co-3dx²-y² orbitals on the kagome lattice. At an electron filling of 5/6, this model reproduces the experimentally observed magnetism and results in a reduction of the Coulomb interaction due to cluster effects. This reduced value of Hubbard U leads to the Hubbard bands collapsing into a single quasiparticle band across the magnetic transition, creating a correlated metallic state. The consequences of this complex magnetic transition for the topology in this material are discussed with the aid of first principles calculations of the correlated system.