Spin gap in the normal state of Pr-doped and oxygen-deficient RBa2Cu3O7 superconductors

The spin-gap temperatures (T-S) in the normal state of bulk Pr-doped RBa2Cu3O7 (R1-xPTxBa2Cu3O7) and oxygen-deficient RBa2Cu3Ox (R = Yb, Er, Y, Ho, Dy, Gd, Eu, Sm, and Nd) are investigated. The elements on the R sites and the distance between CaO2 planes are found to have no influence on T-S in oxygen-deficient RBa2Cu3Ox in terms of the relationship between the superconducting temperature (T-C) and T-S. However, for R1-xPrxBa2Cu3O7, T-S increases with increasing ionic size of R-site elements for a fixed Pr concentration. Furthermore, by comparing T-S of oxygen-deficient RBa2Cu3Ox to that of R1-xPrxBa2Cu3O7 at the same T-C, it is observed that Pr atoms doped on the R sites not only reduce the carrier density and induce the spin gap, but will also simultaneously suppress T-S. [S0163-1829(98)05837-8].