Incommensurate defect-driven electron correlations in Pr1.85Ce0.15CuO4+δ

We have varied the oxygen defect concentration in Pr2-xCexCuO4+delta and characterized the mean-free path length l and the superconducting coherence length xi of Pr2-xCexCuO4+delta by means of low-temperature transport measurements. Concomitant with the clean-to-dirty crossover around l approximate to xi. we find the emergence of linear resistivity behavior being persistent far into the clean limit (l >> xi). We find a violation of Matthiessen's rule that can be explained by a model of s involving a defect-assisted interlayer channel which acts in parallel with the bandlike conductivity. We observe an unusual dependence of T-c on residual resistivity, inconsistent with the generalized Abrikosov-Gor'kov theory for an order parameter with a single component, providing an important constraint on models of the superconductivity in this material system.