Chiral electronic excitations and strong electron-phonon coupling to Weyl fermions in the Kagome semimetal Co${}_3$Sn${}_2$S${}_2$

Abstract

We present results of a Raman scattering study of the Kagome ferromagnet Co${}_3$Sn${}_2$S${}_2$, with a focus on electronic and phononic excitations and their interplay. We provide a theoretical analysis of the electronic band structure, enabling a semi-quantitative explanation of the spectra. A prominent feature in the electronic spectra is a redistribution of spectral weight from low to high energies in all polarization configurations starting at the Curie temperature T${}_C$. In the symmetry-resolved spectra, the suppression of the A${}_{1g}$ continuum in the ferromagnetic state arises from the redistribution of electronic states below T${}_C$, while a strong enhancement of the A${}_{2g}$ continuum is linked to the dynamics of fermions near the Fermi level $E_{\mathrm{F}}$ being characterized by spin-momentum locking near Weyl points. The A${}_{1g}$ phonon modulates the position of these Weyl points and couples strongly to the related fermions close to $E_{\mathrm{F}}$. These results allow a comprehensive understanding of the bulk band structure evolution as a function of temperature in Co${}_3$Sn${}_2$S${}_2$, offering key insights for further studies of the driving force behind the long-range magnetic order and novel topological states in this compound.

9 pages, 4 figures