Universal temperature dependence, flux extinction, and the role of 3He impurities in superfluid mass transport through solid 4He.

The mass flux, F, carried by as-grown solid (4)He in the range 25.6-26.3 bar rises with falling temperature, and at a concentration-dependent temperature, T(d), the flux decreases sharply within a few mK. We study F as a function of (3)He impurity concentration, χ. We find that T(d) is an increasing function of increasing χ. At temperatures above T(d) the flux has a universal temperature dependence and the flux terminates in a narrow window near a characteristic temperature T(h) ≈ 625 mK, which is independent of χ.

Mass flux characteristics in solid 4He for T>100 mK: evidence for bosonic Luttinger-liquid behavior.

At a pressure of ~25.7 bar, the flux F carried by solid (4)He for T>100 mK depends on the net chemical potential difference between two reservoirs in series with the solid, Δµ, and obeys F~(Δµ)(b), where b≈0.3 is independent of temperature. At fixed Δµ the temperature dependence of the flux F can be adequately represented by F~-ln(T/τ), τ≈0.6 K, for 0.1≤T≤0.5 K. A single function F=F(0)(Δµ)(b)ln(T/τ) fits all of the available data sets in the range 25.6-25.8 bar reasonably well. We suggest that the mass flux in solid (4)He for T>100 mK may have a Luttinger liquidlike behavior in this bosonic system.

Mass flux and solid growth in solid 4He for 60-700 mK.

We use the thermomechanical effect to confirm that a flux of atoms takes place in hcp solid 4He below ∼600 mK. We find that the flux falls abruptly in the vicinity of 80 mK and rises with further reduction of temperature. Samples freshly made at 60 mK do not allow mass flux and cannot be grown off the melting curve even when raised in temperature to 200 mK. Solids created above ∼300 mK and cooled to 60 mK can be grown further and demonstrate finite mass flux.

Observation of unusual mass transport in solid hcp (4)He.

Solid (4)He has been created off the melting curve by growth at a nearly constant mass via the "blocked capillary" technique and growth from the (4)He superfluid at constant temperature. The experimental apparatus allows injection of (4)He atoms from superfluid directly into the solid. Evidence for the superfluidlike transport of mass through a sample cell filled with hcp solid (4)He off the melting curve is found. This mass flux depends on temperature and pressure.

Unexpected Mass Decoupling for 3He-4He Films on a Solid Hydrogen Substrate.

Quartz oscillator measurements reveal new behavior in 3He-4He mixture films on a H2 substrate. For mixture films of total coverage greater than one monolayer, in addition to the expected Kosterlitz-Thouless transition, a second mass decoupling event is observed, which behaves differently from the Kosterlitz-Thouless transition.

Observation of two-dimensional classical wave localization: third sound on superfluid 4He films on a disordered substrate.

We present the results of measurements of the propagation of third sound waves on superfluid 4He adsorbed to two-dimensional ordered and disordered substrates. In the disordered case we compare the experimental results to theoretical predictions of classical wave localization in such systems and conclude that classical wave localization is present in our system.

Statistical characterization of thermally evaporated rough CaF2 films.

Thermal deposition of CaF2 onto a glass substrate creates a nanoscale rough surface. A series of samples with differing nominal CaF2 film thicknesses have been fabricated, and the topography has been investigated using atomic force microscopy. Measured values for the statistical characterization of the samples are presented including the exponents describing the scaling behavior of the surfaces. We find that the roughness exponent alpha=0.88+/-0.03 , the growth exponent beta=0.75+/-0.03 , and the dynamical exponent z=alpha/beta=1.17+/-0.06 . We also measure the multifractal spectra and nearest neighbor height difference probability distribution. The results are consistent with noise dominated by a power-law distribution with exponent mu+1 approximately equal to 4.6. Profilometer measurements were used to determine the porosity phi of the deposited films, which we find to be constant for all film thicknesses with phi approximately 0.46 .

Kosterlitz-Thouless transition for 4He films adsorbed to rough surfaces.

We report the study of adsorption isotherms of 4He on several well characterized rough CaF2 surfaces using a quartz crystal microbalance technique at 1.672 K. The signature of decoupled mass observed on crossing the Kosterlitz-Thouless transition as a function of 4He film thickness decreases and becomes increasingly difficult to identify as the surface roughness is increased. A peak in the dissipation, indicative of the onset of superfluidity, changes little with roughness.

Evidence for power-law dominated noise in vacuum deposited CaF2.

We have studied the surface roughness of CaF2 vacuum deposited on glass using atomic force microscopy for film coverages spanning an order of magnitude. We find the roughness exponent alpha=0.88+/-0.03, the growth exponent beta=0.75+/-0.03, and the dynamic exponent z=alpha/beta=1.17+/-0.06. Multifractality is also present, along with power-law behavior in the nearest neighbor height difference probability distribution. The results indicate noise dominated by a power-law distribution with exponent micro+1 approximately 4.6.

Superfluid Avalanches in Nuclepore: Constrained versus Free-Boundary Experiments and Simulations.

Superfluid 4He exhibits hysteretic behavior in the percolated nanoporous material Nuclepore during the filling and draining of pores due to capillary condensation, and one observes avalanches during the pore draining. We observe that the size and frequency of the avalanches depend upon whether the fluid flow off the substrate during draining is impeded or unimpeded. We simulate the draining of superfluid 4He from Nuclepore with and without a perturbation of the pore menisci and find results similar to the results seen in the experiments in the presence or the absence of flow inhibition.

Heat-capacity studies of (3)He in (3)He-(4)He mixture films and the coverage dependence of the two-dimensional (3)He Landau Fermi-liquid parameters.

The heat capacity of (3)He in (3)He-(4)He mixture films on a nuclepore substrate is reported over the temperature range 90

Immunoassay based on surface plasmon oscillations.

An in situ immunoassay technique is described which is sensitive to specific binding to surface immobile antigen or antibody. The phenomena of surface plasmon oscillations are shown to be sensitive to antigen-antibody binding on a substrate. An advantage of the technique is that no molecular labeling is required. The technique allows the detection of the presence of approximately 6 X 10(8) molecules on the approximately 1 mm2 area of detection (approximately 1.5 X 10(-8) g/cm2). An elementary apparatus is described which allows the kinetics of the antigen-antibody binding to be accurately recorded in real time. A detailed example is presented. A second version of the apparatus of similar accuracy with improved temporal resolution is described.