This dissertation presents a Nuclear Magnetic Resonance (NMR) study of anisotropic superconductors, MgB$_2$ and Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212), and diffusion in glass-forming aqueous solutions of glycerol. In glycerol and deuterated water mixtures, the diffusion of glycerol is measured selectively by the $^1$H NMR stimulated echo technique in the gradient field of a superconductive magnet. The breakdown of the Stokes-Einstein (SE) relation is identified in the supercooled stage. Deviation from the SE-relation scales with the water concentration of the mixture. An interpretation is proposed based on the molecular bonding in the system. In the study of the two-gap superconductor MgB$_2$, $^{11}$B NMR spectra of a polycrystalline MgB$_2$ sample are measured in the temperature range between 5 K and 40 K at several magnetic fields. The anisotropy of the coherence length is obtained from the temperature and field dependence of the anisotropy of the spectra. The spectrum in the vortex solid state is simulated with Ginzburg-Landau theory. The penetration depth is estimated to be isotropic at low temperature and the absolute value of the penetration depth is determined from the simulation.</DISS_para> In the study of Bi2212, a highly anisotropic high temperature superconductor, $^{17}$O NMR spectra are measured as a function of temperature and magnetic field in different oxygen doped single crystals. The two-dimensional vortex melting transition is observed in high magnetic fields and the transition temperature is found to be field independent. The symmetry and linewidth from vortices exhibit field dependence from 3 T up to 29 T, indicating the rearrangement of vortices as a function of magnetic field. At high temperature the linewidth of the spectra scales with magnetic field, the temperature dependence of the linewidth follows a Curie temperature dependence, and the inverse of the Curie coefficients is found to be proportional to the non-stoichiometric oxygen, suggesting that there are impurity states induced by oxygen doping in the copper oxygen planes

Last modified

• 05/30/2018

Creator

• Bo Chen

DOI

• https://doi.org/10.21985/N23M6X

Subject

• Physics and Astronomy

Keyword

• Physics

Date created

• 2007-05-14

Resource type

• Dissertation

Rights statement

• In Copyright