Competing charge-density wave instabilities in the kagome metal ScV(6)Sn(6)

Owing to its unique geometry, the kagome lattice hosts various many-body quantum states including frustrated magnetism, superconductivity, and charge-density waves (CDWs). In this work, using inelastic X-ray scattering, we discover a dynamic short-range [Formula: see text] CDW that is dominant in the kagome metal ScV(6)Sn(6) above T(CDW) ≈ 91 K, competing with the [Formula: see text] CDW that orders below T(CDW). The competing CDW instabilities lead to an unusual CDW formation process, with the most pronounced phonon softening and the static CDW occurring at different wavevectors. First-principles calculations indicate that the [Formula: see text] CDW is energetically favored, while a wavevector-dependent electron-phonon coupling (EPC) promotes the [Formula: see text] CDW as the ground state, and leads to enhanced electron scattering above T(CDW). These findings underscore EPC-driven correlated many-body physics in ScV(6)Sn(6) and motivate studies of emergent quantum phases in the strong EPC regime.