Properties of Phase-Separated, Super-Oxygenated La2−x Sr x CuO4+y

We review a series of experiments that have established that super-oxygenated La_2−x Sr _x CuO_4+y phase-separates at low temperature into large magnetic and superconducting regions, driven by the physics of the doped holes themselves. Magnetization studies of trapped flux indicate that the large phase-separated magnetic and superconducting regions develop from nanoscale regions of charge inhomogeneity present in Sr-doped La₂CuO₄ and other more commonly studied cuprates. Neutron studies of the elastic magnetic diffraction show that the peak intensity grows with applied field as in La_2−x Sr _x CuO₄. However, the magnitude of the increase varies widely and is not well accounted for by current theory.