Electronic structure properties and BCS superconductivity in β-pyrochlore oxides: KOs₂O₆

We report a first-principles density-functional calculation of the electronic structure and properties of the recently discovered superconducting β-pyrochlore oxide KOs₂O₆. We find that the electronic structure near the Fermi energy E_F is dominated by strongly hybridized Os 5d and O 2p states. A van Hove singularity very close to E_f leads to a relatively large density of states at E_F, and the Fermi surface exhibits strong nesting along several directions. These features could provide the scattering processes leading to the observed anomalous temperature dependence of the resistivity and to the rather large specific-heat mass enhancement we obtain from the calculated density of states and the observed specific-heat coefficient. An estimate of T_c within the framework of the BCS theory of superconductivity taking into account the possible effects of spin fluctuations arising from nesting yields the experimental value.