Fermi surface of PtCoO₂ from quantum oscillations and electronic structure calculations

The delafossite series of layered oxides includes some of the highest conductivity metals ever discovered. Of these, PtCoO₂, with a room-temperature resistivity of 1.8 μΩcm for in-plane transport, is the most conducting of all. The high conduction takes place in triangular lattice Pt layers, separated by layers of Co-O octahedra, and the electronic structure is determined by the interplay of the two types of layers. We present a detailed study of quantum oscillations in PtCoO₂, at temperatures down to 35 mK and magnetic fields up to 30 T. As for PdCoO₂ and PdRhO₂, the Fermi surface consists of a single cylinder with mainly Pt character and an effective mass close to the free-electron value. Due to Fermi-surface warping, two close-lying high frequencies are observed. Additionally, a pronounced difference frequency appears. By analyzing the detailed angular dependence of the quantum-oscillation frequencies, we establish the warping parameters of the Fermi surface. We compare these results to the predictions of first-principles electronic-structure calculations including spin-orbit coupling on Pt and Co and on-site correlation U on Co, and hence demonstrate that electronic correlations in the Co-O layers play an important role in determining characteristic features of the electronic structure of PtCoO₂.