Incommensurate defect-driven electron correlations inPr1.85Ce0.15CuO4+δ

We have varied the oxygen defect concentration in ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ and characterized the mean-free path length $\ensuremath{\ell}$ and the superconducting coherence length $\ensuremath{\xi}$ of ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ by means of low-temperature transport measurements. Concomitant with the clean-to-dirty crossover around $\ensuremath{\ell}\ensuremath{\approx}\ensuremath{\xi}$ we find the emergence of linear resistivity behavior being persistent far into the clean limit $(\ensuremath{\ell}\ensuremath{\gg}\ensuremath{\xi})$. We find a violation of Matthiessen's rule that can be explained by a model of $\ensuremath{\sigma}$ 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.