Fig. 1: Crystal structure, resistivity of ScV₆Sn₆, and schematics of its CDW formation.

a Crystal structure of ScV₆Sn₆⁴⁵, visualized using VESTA⁷⁰, with the Brillouin zone shown below. The blue circles are q-points probed in this work. b Expansion of the unit cell in the ab-plane for the CDWs in AV₃Sb₅ and ScV₆Sn₆. c The electrical resistivity of ScV₆Sn₆, the inset zooms in around T_CDW. d A comparison of the integrated intensities for q_s-CDW and q^*-CDW, obtained from l-scans centered at (0, 0, 6). The inset zooms out to highlight the rapid growth of q_s-CDW. The triangles represent the absence of a detectable peak. e Schematics of the formation process for CDWs of different origins. A nesting-driven CDW is triggered by a divergent electronic susceptibility χ^″, and phonon softening occurs over a small region in q-space. A conventional EPC-driven CDW results from a peak in the wavevector-dependent EPC and manifests through phonon softening over an extended region in q-space. In these two cases, the peak in χ^″ or EPC, the softest phonon mode, and static CDW order, all occur at the same position in q-space. In ScV₆Sn₆, the softest phonon mode occurs at q^*, whereas static CDW order and the EPC peak occur at a different wavevector q_s. The error bars in (d) are least-square fit errors of 1 s.d.