Angle-resolved photoemission on the delafossite oxide metal PtCoO$_{2}$

The delafossite structural series of oxides has recently attracted considerable attention because of the remarkable and varied properties of the compounds in the series. Here we consider the Pt-based $5d$ delafossite oxide PtCoO$_{2}$, the most conductive oxide known [1]. 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 over 500~meV below E$_{F}$, pointing to suppressed electron-electron scattering. Together, our findings establish PtCoO$_{2}$ as a model nearly-free electron system and an ideal testbed for elucidating the ultrahigh conductivity in delafossite oxides. [1] Kushwaha P. et al., Sci. Adv. {\textbf 1}, 9 (2015)