Origin of the high electrical conductivity of the delafossite metal PdCoO2

Despite being an oxide, the delafossite PdCoO2 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 PdCoO2 at room temperature originates from the contributions of both high Fermi velocities and exceptionally weak electron-phonon coupling, which leads to a coupling strength (lambda = 0.057) that is nearly an order of magnitude smaller than those of common metals. The abnormally weak electron-phonon coupling in PdCoO2 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.