Phase separation in superoxygenated La2-xSrxCuO4+y.

The complex interplay between superconducting and magnetic phases remains poorly understood. Here, we report on the phase separation of doped holes into separate magnetic and superconducting regions in superoxygenated La(2-x)Sr(x)CuO(4+y), with various Sr contents. Irrespective of Sr-doping, excess oxygen raises the superconducting onset to 40 K with a coexisting magnetic spin-density wave that also orders near 40 K in each of our samples.