Hidden kagome-lattice picture and origin of high conductivity in delafossite PtCoO₂

We study the electronic structure of delafossite PtCoO₂ to elucidate its extremely small resistivity and high mobility. The band exhibits steep dispersion near the Fermi level despite the fact that itis formed mainly by Pt d orbitals that are typically localized. We propose a picture based on two hidden kagome-lattice-like electronic structure: one originating from Pt s + p_x/p_y orbitals, and the other from Pt d_3z^2-r^2 + d_xy/d_x^2y^2 orbitals, each placed on the bonds of the triangular lattice. In particular, we find that the underlying Pt s + p_x/p_y bands actually determine the steepness of the original dispersion, so that the large Fermi velocity can be attributed to the large width of the Pt s + p_x/p_y band. In addition, the kagome-like electronic structure gives rise to "orbital-momentum locking" on the Fermi surface, which reduces the electron scattering by impurities. We conclude that the combination of the large Fermi velocity and the orbital-momentum locking is likely to be the origin of the extremely small resistivity in PtCoO₂.