Signatures of spin-momentum locking in the Weyl semi-metal Co₃Sn₂S₂

We present symmetry-resolved Raman spectra of the kagome Weyl semimetal Co$_3$Sn$_2$S$_2$. In the low-energy range, a strongly coupled A1g phonon is observed which clearly experiences the transition into the ferromagnetic state at Curie temperature T_C = 174 K. Our DFT simulations indicate that the band splitting induced by the transition leads to a reduction of the electronic density of states (DOS) at the Fermi energy thus naturally explaining the substantial reduction of the electron-phonon coupling below T_C. Yet the phonon still modulates the band structure sufficiently strongly to make the Weyl points to move in momentum space. At high energies, we find a redistribution of spectral weight in the in A1g and E2g spectra which is compatible with the change of the DOS. In the chiral A2g channel no gap but additional intensity is found in the range of 0.2 eV. Supported by simulations of the resonant Raman response, we interpret the A2g spectra in terms of transitions between the Weyl bands that require a spin flip because of the spin-momentum locking and the resulting textures in k-space.