| Transverse pulsed nuclear magnetic resonance (NMR) measurements performed on three different types of high porosity silica aerogel samples are reported in this thesis. The relative phase stability and order parameter symmetry determined for superfluid 3He confined in the isotropic aerogel, are compared with the globally anisotropic aerogel samples. By straining the aerogel samples, global anisotropy is introduced into an isotropic aerogel. We will refer to compressive strain along the cylinder axis as negative strain, and growth induced stretching as positive strain. Both isotropic and anisotropic aerogel samples are characterized using optical birefringence and cross polarization. Stress-strain measurements were performed to characterize the negatively strained sample.;In the isotropic aerogel sample that was used in several previous experiments, the temperature versus magnetic field phase diagram was measured both on warming and cooling. The first order thermodynamic transition from the B to A-phase on warming displays quadratic field dependence, which extrapolates to the superfluid transition temperature in aerogel at zero magnetic field. This demonstrates that the isotropic B-phase, which corresponds to the Balian-Werthamer (BW) state in zero field, is the equilibrium superfluid state in the presence of isotropic impurity scattering. On cooling from the normal state, the NMR response of the field stabilized A-phase completely vanishes, i.e., the frequency shift, lineshape, and magnetic susceptibility of the A-phase is the same as the normal state, a phenomenon that is consistent with the predicted 3-dimensional (3D) superfluid glass state of the A-phase. On warming from the B-phase, the A-phase displays maximum frequency shift and narrow linewidth, indicative of maximum superfluid order, providing a mechanism for restoring the long range orientational order (LROO) and switching off the glass state.;To study how negatively strained aerogel changes the properties of superfluid 3He, global anisotropy was introduced into isotropic aerogel samples with compressive strain. The temperature versus magnetic field phase diagram of these samples showed that the B-phase is made more stable than the anisotropic A-phase, resulting in a tricritical point for A, B, and normal phases. The critical field was measured to be ~ 100 mT in the aerogel sample with negative strain of ~ -20%. This suggests that the B-phase continuously evolves into an anisotropic B-phase under the influence of aerogel anisotropy. This proposal is supported by the strain dependence of the critical field, as well as the NMR response of the distorted B-phase. Additionally, the 3D glass phase, observed in the isotropic aerogel, was suppressed by the global anisotropy, and LROO was restored along the strain axis, resulting in a continuous 2-dimensional (2D) degeneracy and a 2D glass phase due to random anisotropy perpendicular to the strain axis.;We have also reoriented the positively strained aerogel sample used in previous experiments with strain axis parallel to the magnetic field, in order to determine the direction of the chiral axis relative to the strain axis. Near the superfluid transition temperature Tca, the orbital angular momentum was measured to be parallel to the strain axis, consistent with the theory of Sauls. At low temperature, however, the orbital angular momentum is oriented perpendicular to the strain axis, consistent with the theory of Volovik. A first order disorder transition was observed at Td separating the two different order parameter configurations of the axial state. The tip angle dependent frequency shift of the axial state both above and below Td are fully explored, although a complete quantitative theory is still lacking. |
