INDIRECT EXCHANGE PAIRING - A POSSIBLE KEY TO HIGH-TEMPERATURE SUPERCONDUCTIVITY

Quantitative agreement with experiment provided by a recently proposed indirectexchange mechanism of pairing in high-T, superconductors is illustrated for several specific properties. Within this pairing mechanism, conduction electrons couple due to an indirectexchange interaction between them, via closed-shell oxygen anions. A striking prediction of the theory is the occurrence of a maximum in T, with increasing number of Cu02 layers. In the same framework the recently observed steep decrease in Tc in Bi2(Lnl-, Ce, 0)2Sr2Cu208 (Ln = Sm, Eu or Gd) and BaPbl-, Sb, 03, relative to Bi&aSr2Cu2O8 and BaPbl-, Bi, Os, respectively, can be readily understood. The theory accounts quantitatively for the observed T, of 60 K in the new double-layer superconductor Lal, 60Sro, 40CaCu206T.h e calculated pressure gradient of T, in (La, Ba)-Cu-0 is in agreement with experiment and some hole-doped superconductors are predicted to have negative pressure gradients of T,. In Bi2(Lnl-, Ce, 0)2Sr2Cu208 the value of dln T, IdP is predicted to be 2: 0.6- lo-' kbar-l. © 1990 IOP Publishing Ltd.