Electronic structure properties and BCS superconductivity in beta-pyrochlore oxides: KOs_2O_6

TL;DR

This paper uses first-principles calculations to analyze the electronic structure of KOs_2O_6, revealing features that support its superconductivity within the BCS framework, including a high density of states and Fermi surface nesting.

Contribution

It provides the first detailed electronic structure analysis of KOs_2O_6, linking Fermi surface features to its superconducting properties and estimating T_c from BCS theory.

Findings

High density of states at the Fermi level due to van Hove singularity

Strong Fermi surface nesting along several directions

Estimated T_c matches experimental value

Abstract

We report a first-principles density-functional calculation of the electronic structure and properties of the recently discovered superconducting beta-pyrochlore oxide KOs_2O_6. 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.