Flux pinning and phase separation in oxygen rich La2-xSrxCuO4+y system

We have studied the magnetic characteristics of a series of super-oxygenated La2-xSrxCuO4+y samples. As shown in previous work, these samples spontaneously phase separate into an oxygen rich superconducting phase with a TC near 40 K and an oxygen poor magnetic phase that also orders near 40 K. All samples studied are highly magnetically reversible even to low temperatures. Although the internal magnetic regions of these samples might be expected to act as pinning sites, our present study shows that they do not favor flux pinning. Flux pinning requires a matching condition between the defect and the superconducting coherence length. Thus, our results imply that the magnetic regions are too large to act as pinning centers. This also implies that the much greater flux pinning in typical La2-xSrxCuO4 materials is the result of nanoscale inhomogeneities that grow to become the large magnetic regions in the super-oxygenated materials. The superconducting regions of the phase separated materials are in that sense cleaner and more homogenous than in the typical cuprate superconductor.Comment: 4 figures 8 pages Submitted to PR

Electronic phase separation in super-oxygenated La2-xSrxCuO4+y

We studied microscopic and macroscopic properties of a series of superconducting La2-xSrxCuO4+y samples with various Sr contents. These samples are unique as they are doped with excess oxygen using wet chemical techniques. The properties of the system were studied by means of muon spin rotation (μSR), neutron scattering and bulk magnetization experiments. We have determined that the superoxygenated La2-xSrxCuO4+y system undergoes an electronically driven phase separation of doped holes into separate magnetic and superconducting regions. In the range where x is ≤ 1/8, we found that excess oxygen raises the superconducting onset temperature close to 40 K with a coexisting magnetic ordering temperature that also orders near 40 K. Neutron scattering experiments indicate the presence of incommensurate magnetism, consistent with previous reports on 1/8 th hole doped magnetic materials. Thus we determined the magnetic regions of our phase separated system to be anomalous, 1/8 th hole doped, magnetic versions of La2-xSr xCuO4, and the superconducting regions to be optimally doped versions of La2-xSrxCuO4. The superconducting and magnetic phases in the oxygen rich La 2-xSrxCuO4+y system seem to be the only stable ground states in the hole-rich side of the phase diagram. This simple two-component system is a key to understanding seemingly conflicting experimental observations and will give a new insight to the understanding of cuprate based high temperature superconductors.