A series of neutron scattering studies of unconventional superconductors is presented.
These measurements are split into two parts. The first part considers the purely
magnetic scattering in low-doped $La_{2−x}Ba_{x}CuO_{4}$. This study is comprehensive and elucidates much of the doping and temperature dependence of the low energy magnetic
scattering in this system. It also clearly demonstrates that two dimensional incommensurate
magnetic order in this system forms at the expense of three dimensional
commensurate magnetic order. The remainder of the thesis is concerned with characterizing
and determining the physics underlying pronounced enhancements of the
inelastic scattering found to exist at 20 meV at equivalent two dimensional magnetic
zone centers in both $La_{2−x}Ba_{x}CuO_{4}$ and $La_{2−x}Sr_{x}CuO_{4}$. Arguments are presented to interpret these features as a result spin-phonon hybridization in 214 cuprate superconductors. The measurements also explore the temperature and doping dependence of these features, determining that the enhancements are largely insensitive to doping and only present parametric response at temperatures relevant for three dimensional
magnetic order in this system. In addition, the first evidence for a superconducting spin
gap in $La_{2−x}Ba_{x}CuO_{4}$ is presented. The implications of these findings are discussed. / Thesis / Doctor of Philosophy (PhD) / This thesis discusses a series of measurements using brand new state of the art facilities to re-examine the family of high temperature superconductors with the simplest structure. By taking advantage of these new facilities and applying their capabilities to a, relatively speaking, simpler material family, the goal is to try and learn more about what may be the cause of high temperature superconductivity - a magnetism based phenomenon with profound implications for energy efficiency, energy storage, diagnostic healthcare, quantum computing and much more. While many interesting effects were observed, two of the more important findings were observations that unify the physical descriptions of $La_{2−x}Ba_{x}CuO_{4}$ and $La_{2−x}Sr_{x}CuO_{4}$, as is necessary to have a truly universal understanding of high temperature superconductivity, and a detailed characterization we interpret as hybridization. It is clear from this work that any complete solution of superconductivity must also explain this part magnetic and part crystalline structural hybridization phenomenon.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18173 |
| Date | 11 1900 |
| Creators | Wagman, Jerod Justin |
| Contributors | Gaulin, Bruce D., Physics and Astronomy |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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