Transition metal ion substitution into the Cu(1) sites in the "123" high-temperature superconductors

Abstract

The effects of substituting either non-magnetic or magnetic (trivalent) transition metal (TM) ions into the Cu(1) sites in the CuO chains occurring in the "123" YBa2Cu3O7-xsuperconductor are studied. It is assumed that pair condensation occurs in both the 2D CuO2planes and the 1D CuO chains, that the exchange of the spin fluctuations (SF) is responsible for the pair formation and that the order parameters in the chains and planes are coupled together by pair tunneling. Just like the case for substitution into the Cu(2) sites, the depressions of Tcdue to non-magnetic and magnetic TM ions substitution into the Cu(1) sites are caused by the different ways the two type of ions act on the Cooper pairs. The non-magnetic TM ions suppress the formation of the Cooper pairs through their suppression of the SF-induced pairing interaction while the magnetic TM ions break the Cooper pairs through their sping flipping of one of the carriers. For both types of ions, the suppression of superconductivity is enhanced by the normal scattering process.