Results of highly precise all-electron local density calculations of the electronic structure for the high Tc superonductors (La2-xMxCuO4, YBa2Cu3O7-δ, Bi2Sr2CaCu2O8, Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10), as determined with the full potential linearized augmented plane wave (FLAPW) method are presented. In all these high Tc materials, the Cu-O dpσ (anti-bonding) bands arising from the CuO2 planes cross EF and are strongly two-dimensional. The Y, Ba, Sr, and Ca atoms are highly ionic with the Ca2+ ions serving to insulate the Cu-O planes. In both Bi2Sr2CaCu2O8 and the Tl compounds, the Bi-O and Ti-O planes contribute to the density of states at EF and hence to the transport properties. The similarity and difference between these systems are described in detail. The results obtained demonstrate the close relation of the band structure to the structural arrangements of the constituent atoms and provide an integrated chemical and physical picture of their interactions and their possible relation to the origin of their high Tc superconductivity. Our calculations indicate the inadequacy of a purely electron-phonon mechanism in explaining the high Tc. An excitonic mechanism of superconductivity is discussed.
ASJC Scopus subject areas
- Chemical Engineering(all)