Anomalous electron-phonon coupling in the Kagome ferromagnetic Weyl semimetal Co₃Sn₂S₂

We present a theoretical analysis based on first principles of the Raman response from the magnetic Kagome Weyl semimetal Co₃Sn₂S₂. Two Raman active phonon modes have been identified in A_1g and E_g symmetry, with strong electron-phonon coupling (EPC) to the A_1g phonon above the ferromagnetic phase transition temperature T_C. Density functional theory (DFT) calculations accurately predict the experimentally observed A_1g and E_g phonon energies, and the phonon eigenvectors provide insight into the source of the electron-phonon coupling. A phenomenological approach allows us to quantify the observed EPC in the Raman spectrum, while first principles methods allow us to characterize the nature of the EPC for both modes. The strong electron-phonon coupling in A_1g can be explained by the asymmetric crystal field felt by the Co atoms: out-of-plane motion of the S atoms results in both intraband and interband EPC, the latter resulting in significant asymmetry in the Raman peak. These results give us a comprehensive understanding of the bulk band structure evolution as a function of temperature in Co₃Sn₂S₂, which paves the way for further study of the driving force of the long-range magnetic order and more emergent effects in this and similar compounds.