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We have measured the energy dependence of roton quantum evaporation. A transiently heated cavity filled with superfluid
He generates R+ and R− rotons. The emitted rotons are collimated and arrive at the free liquid surface with a narrow range of incident angles. We detect two beams of...
We describe procedure and main results of numerical simulations on the response of the vortex sheet in
He-A to changes in the rotation velocity. The response is studied for different configurations of the sheet consisting of single or multiple pieces. The behavior of the vortex sheet is found...
The importance of Castaing instabilities in θ−Δt−π spin-echo experiments in spin-polarized normal Fermi fluids is investigated. For small tip angles and very large values of the spin rotation parameter μM, a previous stability analysis is extended to account for angular relaxation, an effect...
We report simultaneous heat capacity and torsional oscillator measurement of
He in aerogel near the superfluid transition. The heat capacity has a peak at the temperature Tc where the torsional oscillator shows the onset of superfluid decoupling. The coincidence of these signatures suggests...
Far from the lambda transition the critical flow of superfluid
He through a small orifice is determined by thermal nucleation of quantized vortices. Between 300 mK and 2 K linearly decreasing critical flow velocity has been observed earlier. As the temperature approaches Tλ the size of the...
We have been searching for two-dimensional (2-D) superfluidity of spin-polarized atomic hydrogen (H↓) adsorbed on liquid helium surface. We have investigated H↓ adsorbed on
He mixtures instead of pure
He because the thermal coupling of H↓ to the mixtures is stronger than
He. ESR at...
We have performed simultaneous adsorption isotherm and small angle x-ray scattering (SAXS) measurements of
He adsorption into 98% porous aerogel at 3.5K. Measurements indicate a two phase coexistence at vapor pressures slightly below the bulk liquid-vapor equilibrium point. SAXS data are...
The persistent induction signal (PIS) is an extremely long lived NMR mode in the B-phase of superfluid
He. The first signals observed lived for up to 25s following a moderate NMR tipping pulse, but were found to be highly irreproducible. Here we present new measurements obtained in a smooth...
We have designed and built a demagnetization stage to operate between 1.8K and 0.5K, a somewhat unusual temperature range for adiabatic demagnetization refrigeration. The lower bound in temperature is dictated by the thermal performance of our
He gas heat switch, the upper by NASA...
For thin films of
He at low temperatures the addition of sub-monolayer numbers of
He atoms results in the
He residing in a ground state at the free surface of the
He film. For low
He coverage the
He are a nearly ideal two-dimensional Fermi system. With increasing numbers of
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