Phonon mixing in the charge density wave state of ScV_6Sn_6

Kagomé metals are widely recognized, versatile platforms for exploring topological properties, unconventional electronic correlations, magnetic frustration, and superconductivity. In the R V_6Sn_6 family of materials ( R = Sc, Y, Lu), ScV_6Sn_6 hosts an unusual charge density wave ground state as well as structural similarities with the A V_3Sb_5 system ( A = K, Cs, Rb). In this work, we combine Raman scattering spectroscopy with first-principles lattice dynamics calculations to reveal phonon mixing processes in the charge density wave state of ScV_6Sn_6. In the low temperature phase, we find at least four new peaks in the vicinity of the V-containing totally symmetric mode near 240 cm^−1 suggesting that the density wave acts to mix modes of P 6/ m m m and $$R\bar{3}m$$ R 3 ¯ m symmetry - a result that we quantify by projecting phonons of the high symmetry state onto those of the lower symmetry structure. We also test the stability of the short-range ordered density wave state under compression and propose that both physical and chemical pressure quench the effect. We discuss these findings in terms of symmetry and the structure-property trends that can be unraveled in this system.