Chiral electronic excitations and strong electron-phonon coupling to Weyl fermions in the kagome semimetal Co 3 Sn 2 S 2

Near a Weyl point, spin-momentum locking forces opposite spin orientations above and below the node. When a Weyl point lies near the Fermi surface, electrons can scatter across it only by flipping spin, thereby breaking time-reversal symmetry. This process appears exclusively in the antisymmetric $A$${}_{2g}$ Raman channel. The authors observe here enhanced $A$${}_{2g}$ intensity below the ferromagnetic transition of Co${}_{3}$Sn${}_{2}$S${}_{2}$, providing strong evidence for Weyl points. Furthermore, the calculated resonant $A$${}_{2g}$ response shows qualitative agreement with experiment.