# Hidden kagome-lattice picture and origin of high conductivity in delafossite PtCoO$_2$

## TL;DR

This paper reveals that the high conductivity in delafossite PtCoO$_2$ stems from a hidden kagome-lattice electronic structure, large Fermi velocity, and orbital-momentum locking, which together reduce electron scattering and enable high mobility.

## Contribution

It introduces a novel hidden kagome-lattice picture in PtCoO$_2$'s electronic structure, explaining its high conductivity and low resistivity.

## Key findings

- Steep dispersion near the Fermi level from Pt s+p orbitals.
- Kagome-like electronic structure causes orbital-momentum locking.
- Large Fermi velocity due to wide Pt s+p band.

## Abstract

We study the electronic structure of delafossite PtCoO$_2$ to elucidate its extremely small resistivity and high mobility. The band exhibits steep dispersion near the Fermi level despite the fact that it is 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 $d_{3z^2-r^2}+d_{xy}/d_{x^2-y^2}$ 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. More importantly, 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 PtCoO$_2$.