Origin of the high electrical conductivity of the delafossite metal PdCoO2

Despite being an oxide, the delafossite ${\mathrm{PdCoO}}_{2}$ has an exceptionally high electrical conductivity that rivals those of the most conductive elemental metals, enabling a multitude of exotic transport phenomena. However, the reasons behind its unusually high electrical conductivity remained elusive for decades. Using first-principles transport calculations and theoretical modeling, we reveal that the ultrahigh electrical conductivity of ${\mathrm{PdCoO}}_{2}$ at room temperature originates from the contributions of both high Fermi velocities and exceptionally weak electron-phonon coupling, which leads to a coupling strength ($\ensuremath{\lambda}=0.057$) that is nearly an order of magnitude smaller than those of common metals. The abnormally weak electron-phonon coupling in ${\mathrm{PdCoO}}_{2}$ results from a low electronic density of states at the Fermi level, as well as the large and strongly facetted Fermi surface with suppressed Umklapp electron-phonon matrix elements. The insights gained from this work provide critical guidance for designing unconventional metals with superior electron transport properties.