Electronic structure and topology across $T_c$ in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$

TL;DR

This study investigates the electronic structure and topological changes in the magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ across its Curie temperature, revealing a transition from a Mott ferromagnet to a correlated metal with distinct spectral signatures.

Contribution

It provides a combined experimental and theoretical analysis of the temperature-dependent electronic and topological properties of Co$_3$Sn$_2$S$_2$, highlighting the role of reduced Coulomb interactions and magnetic transition effects.

Findings

Large band shifts and renormalization across $T_c$

Collapse of bands due to reduced Hubbard-$U$

Distinct photoemission signatures of the magnetic transition

Abstract

Co$_3$Sn$_2$S$_2$ 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 ($T_c$), which show large band shifts and renormalization concomitant with the onset of magnetism. We argue that Co$_3$Sn$_2$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.