Band structure of metallic pyrochlore ruthenates Bi₂Ru ₂O₇ and Pb₂Ru₂O_6.5

The band structure of Bi₂Ru₂O₇ and Pb ₂Ru₂O_6.5 has been computed self-consistently from first principles for the first time by the pseudofunction method. We discover that the 6s bands of Bi and Pb are very deep and unlikely to contribute to the metallic behavior as previously believed. The unoccupied 6p bands, however, are only several eV above the Fermi energy and are mixed with the Ru 4d band at the Fermi surface via the framework O atoms, leading to band conduction and delocalized magnetic moments. The predicted location of the 6s bands and the location and width of the O 2p band are confirmed by synchrotron radiation and ultraviolet electron spectroscopy of single crystals.