${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ is a magnetic Weyl semimetal, in which ferromagnetic ordering at 177 K is predicted to stabilize Weyl points. We perform temperature and spatial dependent angle-resolved photoemission spectroscopy measurements through the Curie temperature ($T_c$), which show large band shifts and renormalization concomitant with the onset of magnetism. We argue that ${\mathrm{Co}}_3{\mathrm{Sn}}_2{\mathrm{S}}_2$ evolves from a Mott ferromagnet below $T_c$ to a correlated metallic state above $T_c$. To understand the magnetism, we derive a tight-binding model of Co-$3d_{x^2-y^2}$ 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 $T_c$ is discussed in the context of this description of the magnetism.

• Received 18 May 2021
• Revised 1 August 2021
• Accepted 24 September 2021
• Corrected 2 November 2021

DOI:https://doi.org/10.1103/PhysRevB.104.155115