Title

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

Date of Completion

January 2006

Keywords

Physics, Condensed Matter

Degree

Ph.D.

Abstract

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. ^