SUPERCONDUCTIVITY IN Ba_1-xK_xBiO₃: POSSIBLE SCENARIO OF SPATIALLY SEPARATED FERMI-BOSE MIXTURE
Menushenkov A.P., Klementev K.V., Kuznetsov A.V., Kagan M.Yu.

Received: March 16, 2001

PACS: 74.20.Mn, 74.72.Yg

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We propose a new scenario for the metal-insulator phase transition and superconductivity in the perovskite-like bismuthates Ba_1-xK_xBiO₃ (BKBO) based on our EXAFS studies. We show that two types of charge carriers, the local pairs (real-space bosons) and the itinerant electrons, exist in the metallic compound Ba_1-xK_xBiO₃ (). The real-space bosons are responsible for the charge transport in semiconducting BaBiO₃ and for superconductivity in the metallic BKBO. The appearance of the Fermi-liquid state as the percolation threshold is overcome () explains the observed metal-insulator phase transition. Because bosons and fermions occupy different types of the octahedral BiO₆ complexes, they are separated in real space, and therefore, the spatially separated Fermi-Bose mixture of a new type is likely to be realized in the bismuthates. The nature of superconductivity is consistently explained in the framework of this scenario. A new superconducting oxide Ba_1-xLa_xPbO₃ has been successfully synthesized to check our conclusions.