Nuclear magnetic resonance study of anisotropic superconductors and diffusion in glass-forming aqueous mixtures of glycerol.

摘要

This dissertation presents a Nuclear Magnetic Resonance (NMR) study of anisotropic superconductors, MgB2 and Bi2Sr2CaCu 2O8+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 1H 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 MgB2, 11 B NMR spectra of a polycrystalline MgB2 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.;In the study of Bi2212, a highly anisotropic high temperature superconductor, 17O 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.