Authors: JOHN A. WILSON, ALİ İHSAN DEMİREL
Abstract: The \( p/d \) hybridization that primarily characterizes copper leads to local moments, lacking of the pair-breaking variety, both at di- and trivalent sites. Support for the negative-U model is extracted from the author's earlier work on the metal-insulator transition. A more magnetically oriented model, like the resonant valence band model which we have recently associated with our observations in d1 TiOCl etc., does not really seem suited to the geometry and electronic conditions in the copper oxides present. However it is suggested that TiB$_2$, La$_3$S$_4$ and the Chevrel phases might be open to treatment by such a model. Comment it also made about how the superconductivity of PdH$_x$ and Ba(Pb/Bi)O$_3$ might be seen in the light of the present model, and attention is directed once again to what might be happening in the pressure-quenched CuCl and CdS.
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