Phonon mixing in the charge density wave state of ScV₆Sn₆

Kagome metals are widely recognized, versatile platforms for exploring topological properties, unconventional electronic correlations, magnetic frustration, and superconductivity. In the RV₆Sn₆ family of materials (R = Sc, Y, Lu), ScV₆Sn₆ hosts an unusual charge density wave ground state as well as structural similarities with the AV₃Sb₅ 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 ScV₆Sn₆. 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 P6/mmm and R ̅3m 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.