Condensed-Matter Physics Seminar

The physics of high temperature superconductors in particular, and transition metal oxides in general, is that of strongly interacting, localized electrons. It has long been recognized that under many conditions strongly interacting electrons might not form a homogenous
electron sea but rather intrinsically phase separate into just a few stable phases, notably hole rich and hole poor regions. Several experimental candidates have been found for such a phase separation in the high temperature superconductors, but in no case has it been clear that the observed phenomenon was both true phase separation and
electronically driven. And typically the relationship of the phenomenon to superconductivity has not been clear. We have produced samples of the rarely studied system La2-xSrxCuO4+y using starting compounds with various x values (Sr content) and oxidized with an electrochemical
technique. A combination of muon spin rotation (mSR) and magnetization measurements give a convincing case for an electronically driven phase separation in these samples between a nonsuperconducting, magnetic phase and a nonmagnetic, superconducting phase. I present the evidence for the phase separation, its electronic nature, and discuss some implications for current issues in high Tc superconductivity.