First-Principles Calculations on β-Pyrochlore Superconductors AOs₂O₆ (A = K, Rb, Cs)

We report first-principles calculations of the electronic structures and properties of superconducting beta-pyrochlore oxides AOs(2)O(6) (A = K, Rb, Cs). The values of electronic density of states at the Fermi level have been significantly enhanced for the three compounds by considering the spin-orbit coupling and the on-site Coulomb interactions. The electronic Coulomb correlation constants lambda (c) =1.55, 1.12 and 0.73 are obtained. Analyzing the electronic mass enhancement parameters obtained from the experimental data and the calculated electronic density of states, we deduce the electron-phonon coupling constants lambda (ep)=1.56, 0.78 and 1.08 for the three compounds, respectively. It is suggested that KOs2O6 is a strong-correlated and strong electron-phonon coupled system, while RbOs2O6 and CsOs2O6 are intermediate-correlated ones. The novel superconductivities of KOs2O6 are also discussed.