Superstructural lattice distortion within electron doped superconductor Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4}$*

It is well-known that electron-doped Nd$_{0.85}$Ce$_{0.15}$CuO$_{4}$ can be reversibly converted between the superconductor and non-superconductor by appropriate high-temperature treatments in reducing or oxidizing environments, respectively. Samples that exhibit superconductivity also present a crystalline Nd$_{2}$O$_{3}$ (bixbyite structure) impurity phase as well as diffuse (0, 0, L) rods of scattering at superlattice positions in the (H, K, 0) plane that coincide with the reciprocal lattice of the larger 2$\surd $2 $\times $ 2$\surd $2 impurity cell. We present a diffuse scattering analysis of the rod scattering in related compound Pr$_{0.88}$LaCe$_{0.12}$CuO$_{4}$ (PLCCO) and demonstrate that they are evidence of a superstructural distortion of the CuO$_{2}$ sheets, rather than an impurity effect. This in-plane superstructure may prove to be a necessary condition for superconductivity in the electron-doped cuprates.