Electronic Structure and Valence-Bond Band Structure of Cuprate Superconducting Materials

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Science  19 Feb 1988:
Vol. 239, Issue 4842, pp. 896-899
DOI: 10.1126/science.239.4842.896


From ab initio calculations on various clusters representing the La2-xSrxCu1O4 and Y1Ba2Cu3O7 classes of high-temperature superconductors, it is shown that (i) all copper sites have a CuII(d9)oxidation state with one unpaired spin that is coupled antiferromagnetically to the spins of adjacent CuII sites; (ii) oxidation beyond the cupric (CuII) state leads not to CuIII but rather to oxidized oxygen atoms, with an oxygen pπ hole bridging two CuII sites; (iii) the oxygen pπhole at these oxidized sites is ferromagnetically coupled to the adjacent CuIId electrons despite the fact that this is opposed by the direct dd exchange; and (iv) the hopping of these oxygen pπ holes (in CuO sheets or chains) from site to site is responsible for the conductivity in these systems (N-electron band structures are reported for the migration of these localized charges).