UC Davis

Co3Sn2S2 is a magnetic Weyl semimetal, in which ferromagnetic ordering at 177K is predicted to stabilize Weyl points. We perform temperature and spatial dependent angle--resolved photoemission spectroscopy measurements through the Curie temperature (Tc), which show large band shifts and renormalization concomitant with the onset of magnetism. We argue that Co3Sn2S2 evolves from a Mott ferromagnet below Tc to a correlated metallic state above Tc. To understand the magnetism, we derive a tight-binding model of Co-3dx2−y2 orbitals on the kagome lattice. At the filling obtained by first-principles calculations, this model reproduces the ferromagnetic ground state, and results in the reduction of Coulomb interactions due to cluster effects. Using a disordered local moment simulation, we show how this reduced Hubbard-U leads to a collapse of the bands across the magnetic transition, resulting in a correlated state which carries associated characteristic photoemission signatures that are distinct from those of a simple lifting of exchange splitting. The behavior of topology across Tc is discussed in the context of this description of the magnetism.