Fig. 5

a The factors α (circles) and β (triangles) as defined in the main text for PtCoO₂ (orange) and PdCoO₂ (purple), respectively. Data for β for PdCoO₂ are included for completeness, but are less reliable because the extremely low resistivity at low temperatures leads to larger relative error in its estimation. In panel b we show the results of model calculations (described in Methods) for the ratio r of the weak- to strong-field Hall coefficients predicted for a Fermi surface approximated to a hexagon with rounded corners. Because the weak-field Hall conductivity is dominated by regions of high Fermi surface curvature, whereas the high-field Hall coefficient is independent of Fermi surface topography, the experimentally observed value of r = 0.3 (dotted line) can phenomenologically be accounted for by a factor δ suppressing the mean free path on the Fermi surface corners relative to that on the faces. Depending on the value chosen for the curvature factor η, δ varies between 0.3 and 0.6