Understanding the role of electron correlations in strong spin-orbit transition-metal oxides is key to the realization of numerous exotic phases including spin-orbit–assisted Mott insulators, correlated topological solids, and prospective new high-temperature superconductors. To date, most attention has been focused on the 5 d iridium-based oxides. We instead consider the Pt-based delafossite oxide PtCoO 2 . Our transport measurements, performed on single-crystal samples etched to well-defined geometries using focused ion beam techniques, yield a room temperature resistivity of only 2.1 microhm·cm (μ-cm), establishing PtCoO 2 as the most conductive oxide known. From angle-resolved photoemission and density functional theory, we show that the underlying Fermi surface is a single cylinder of nearly hexagonal cross-section, with very weak dispersion along k z . Despite being predominantly composed of d -orbital character, the conduction band is remarkably steep, with an average effective mass of only 1.14 m e . Moreover, the sharp spectral features observed in photoemission remain well defined with little additional broadening for more than 500 meV below E F , pointing to suppressed electron-electron scattering. Together, our findings establish PtCoO 2 as a model nearly-free–electron system in a 5 d delafossite transition-metal oxide.
Natural Sciences in General