NEUTRON SCATTERING STUDIES OF STRONG DYNAMIC CORRELATIONS IN UNCONVENTIONAL SUPERCONDUCTORS: LOOKING THROUGH THE HOUR-GLASS TO HYBRIDIZATION AND A SUPERCONDUCTING SPIN RESONANCE

Abstract

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.