PhD Dissertation Defense

Electronic Phase Separation in Oxygen Doped La2-xSrxCuO4+y System

Hashini Mohottala
Physics Department

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 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 ≤ 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 1/8th hole doped magnetic materials. Thus we determined the magnetic regions of our phase separated system to be anomalous, 1/8th hole doped, magnetic versions of La2-xSrxCuO4, and the superconducting regions to be optimally doped versions of La2-xSrxCuO4. The superconducting and magnetic phases in the oxygen rich La2-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 theory of cuprate based high temperature superconductors.

Thursday, December 14, 2006
1:00 pm
Gant Science Complex
Physics Department
Room P121

(Refreshments will be served before and after the defense in the Physics Library, Room P-103)

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