Fig. 1: Conduction (negative) and valence (positive) standard Fröhlich model ZPR^sFr and α values, for all but 10 (0) materials where the valence (conduction) ZPR^sFr exceeds 3000 meV.

The ZPR^sFr values are determined based on the full range coupling strength described in Eq. (46). The color corresponds to chemical elements from groups 15 to 17 of the periodic table (see inset), and brown for all other compounds. Materials with compounds from group 17 are more concentrated in the α < 5 domain, while materials with compounds from groups 16 and 14 have wider spreads. All classes of compound show outliers with very large α. Valence values are distributed over a wider range of α, and conduction values are more concentrated below α = 5. The vertical dashed line is at α = 6. An equivalent figure based on the full range α based on Feynman’s approach is provided in Supplementary Fig. 8.