Acoustic Spectroscopy of Superfluid 3He in Aerogel

We have designed an experiment to study the role of global anisotropic quasiparticle scattering on the dirty aerogel superfluid 3He system. We observe significant regions of two stable phases at temperatures below the superfluid transition at a pressure of 25 bar for a 98% aerogel.Comment: 2 pages, 2 figures, accepted for publication in proceedings of Low Temperature Conference 2

Charge metastability and hysteresis in the quantum Hall regime

We report simultaneous quasi-dc magnetotransport and high frequency surface acoustic wave measurements on bilayer two-dimensional electron systems in GaAs. Near strong integer quantized Hall states a strong magnetic field sweep hysteresis in the velocity of the acoustic waves is observed at low temperatures. This hysteresis indicates the presence of a metastable state with anomalously high conductivity in the interior of the sample. This non-equilibrium state is not revealed by conventional low frequency transport measurements which are dominated by dissipationless transport at the edge of the 2D system. We find that a field-cooling technique allows the equilibrium charge configuration within the interior of the sample to be established. A simple model for this behavior is discussed.Comment: 8 pages, 4 postscript figure

Specific Heat of Disordered 3^{3}He

Porous aerogel is a source of elastic scattering in superfluid 3He and modifies the properties of the superfluid, suppressing the transition temperature and order parameter. The specific heat jumps for the B-phase of superfluid 3He in aerogel have been measured as a function of pressure and interpreted using the homogeneous and inhomogeneous isotropic scattering models. The specific heat jumps for other p-wave states are estimated for comparison.Comment: Manuscript prepared for LT 2

Anisotropic Aerogels for Studying Superfluid 3^3He

It may be possible to stabilize new superfluid phases of $^{3}$He with anisotropic silica aerogels. We discuss two methods that introduce anisotropy in the aerogel on length scales relevant to superfluid $^{3}$He. First, anisotropy can be induced with uniaxial strain. A second method generates anisotropy during the growth and drying stages. We have grown cylindrical $\sim$98% aerogels with anisotropy indicated by preferential radial shrinkage after supercritical drying and find that this shrinkage correlates with small angle x-ray scattering (SAXS). The growth-induced anisotropy was found to be $\sim90^\circ$ out of phase relative to that induced by strain. This has implications for the possible stabilization of superfluid phases with specific symmetry.Comment: 6 pages, 4 figures, submitted to Quantum Fluids and Solids (QFS) conference 200