Ion-size effect on normal-state transport properties in R0.8Pr0.2Ba2Cu3O7-y systems (R=Yb, Er, Dy, Gd, Eu, and Nd).

We report detailed studies of the normal-state resistivity and the Hall-effect in bulk {ital R}{sub 0.8}Pr{sub 0.2}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}} samples ({ital R}=Yb, Er, Dy, Gd, Eu, and Nd). We find a linear temperature dependence of the normal-state resistivity {rho}{sub {ital u}} and the Hall number {ital n}{sub {ital H}} above {ital T}{sub {ital c}} in these systems. At a constant temperature both {rho}{sub {ital n}} and {ital n}{sub {ital H}} are linearly dependent on the ion-size of the rare earth, viz., the larger {ital R}{sup 3+} ionic radius, the larger {rho}{sub {ital n}}, but the lower {ital n}{sub {ital H}}. The cotangent of the Hall angle follows a universal {ital T}{sup 2} dependence, i.e., cot{theta}{sub {ital H}}={alpha}{ital T}{sup 2}+{ital C}. Both the slope {alpha} and the quantity {ital C} is insensitive to the {ital R} ion and remains almost constant. On the basis of our data we propose a {ital T}{sub {ital c}}-{ital n}{sub {ital H}} diagram which manifests an {open_quote}{open_quote}underdoping{close_quote}{close_quote} behavior of {ital R}{sub 0.8}Pr{sub 0.2}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}} systems. We suggest that the strong hybridization between the 4{ital f} states of the Pr ion and the conduction-band states in CuO{sub 2} planes, leading to holemore » localization and pair breaking, are the mechanism for the suppression of superconductivity in {ital R}{sub 1{minus}{ital x}}Pr{sub {ital x}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{ital y}} systems. {copyright} {ital 1996 The American Physical Society.}« less