Bulk Liquid 3He Research Articles

Dynamic properties and the roton mode attenuation in liquid 3He: ab initio study within the self-consistent method of moments.

The dynamic structure factor and the eigenmodes of density fluctuations in liquid 3He are studied using a novel non-perturbative approach. This new version of the self-consistent method of moments invokes up to nine sum rules and other exact relations, the two-parameter Shannon information entropy maximization procedure, and the ab initio path integral Monte Carlo simulations which provide necessary reliable input information on the system static properties. Detailed analysis is performed of the collective excitations dispersion relations, the modes' decrements and the static structure factor of 3He at the saturated vapour pressure. The results are compared to available experimental data by Albergamo et al. (Albergamo et al. 2007 Phys. Rev. Lett. 99, 205301. (doi:10.1103/PhysRevLett.99.205301)) and Fåk et al. (Fåk et al. 1994 J. Low Temp. Phys. 97, 445-487. (doi:10.1007/BF00754303)). The theory reveals a clear signature of the roton-like feature in the particle-hole segment of the excitation spectrum with a significant reduction of the roton decrement in the wavenumber range [Formula: see text]. The observed roton mode remains a well-defined collective mode even in the particle-hole band, where it is strongly damped. The existence of the roton-like mode in the bulk liquid 3He is confirmed like in other quantum fluids. The phonon branch of the spectrum is in a reasonable agreement with the same experimental data. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.

Evidence for 4D XY Quantum Criticality in 4He Confined in Nanoporous Media at Finite Temperatures

$^4$He confined in nanoporous media is a model Bose system that exhibits quantum phase transition (QPT) by varying pressure. We have precisely determined the critical exponent of the superfluid density of $^4$He in porous Gelsil glasses with pore size of 3.0 nm using the Helmholtz resonator technique. The critical exponent $\zeta$ of the superfluid density was found to be 1.0 $\pm$ 0.1 for the pressure range 0.1 < P < 2.4 MPa. This value provides decisive evidence that the finite-temperature superfluid transition belongs to the four-dimensional (4D) XY universality class, in contrast to the classical 3D XY one in bulk liquid 4He, in which $\zeta$ = 0.67. The quantum critical behavior at a finite temperature is understood by strong phase fluctuation in local Bose-Einstein condensates above the superfluid transition temperature. $^4$He in nanoporous media is a unique example in which quantum criticality emerges not only at 0 K but at finite temperatures.

High-temperature supersolid ofHe4in a one-dimensional periodic potential

The search for robust experimental proof of supersolidity has encountered many complicating factors, such as temperature dependent changes in the mechanical properties of solid 4He which mimic the signature of superfluid flow. As a result, the physical existence and true nature of this unique state of matter are still under debate. Here we consider 4He stabilized by a one-dimensional periodic potential whose lattice spacing is similar to the length scale of the 4He-4He interaction. We use the Bogoliubov transformation to calculate the excitation spectrum, finding that when interactions between nearest or next-nearest neighbors are attractive, there is a finite positive gap in energy between the delocalized ground state and the lowest energy excitations which, under certain conditions, is significantly larger than both the melting temperature and the lambda temperature. This means that it should be possible to observe a supersolid at a high enough temperature that superfluidity in bulk liquid 4He or changes in the mechanical properties of bulk solid 4He do not obscure it. The properties of experimentally achievable materials which could support this type of supersolid are also discussed.

Potential generation and path‐integral Monte Carlo in study of microscopic superfluidity

The idea of a macroscopic Andronikashvili experiment used to measure superfluid fraction of bulk liquid 4He can be ported into the realm of spectroscopic studies to measure the superfluid fraction of microscopic systems at the nanoscale. Theoretical studies are needed to fully unravel the superfluid information contained in such a microscopic Andronikashvili experiment. Two aspects of the theoretical studies, the generation of accurate and efficient potential energy surfaces, and the methodology of path‐integral Monte Carlo simulations are briefly introduced in this article. © 2014 Wiley Periodicals, Inc.

The Quest for Bose-Einstein Condensation in Solid 4He

Ever since the seminal torsional oscillator (TO) measurements of Kim and Chan which suggested the existence of a phase transition in solid 4He, from normal to a ‘supersolid’ state below a critical temperature Tc= 200 mK, there has been an unprecedented amount of excitement and research activity aimed at better understanding this phase. Despite much work, this remarkable phase has yet to be independently confirmed by conventional scattering techniques, such as neutron scattering. We have carried out a series of neutron scattering measurements, which we here review, aimed at observing Bose-Einstein condensation (BEC) in solid 4He at temperatures below Tc. In bulk liquid 4He, the appearance of BEC below Tλ signals the onset of superfluidity. The observation of a condensate fraction in the solid would provide an unambiguous confirmation for ‘supersolidity’. Although, our measurements have not yet revealed a non-zero condensate fraction or algebraic off diagonal long-range order n0 in solid 4He down to 65 mK, i.e. n0=(0±0.3)%, our search for BEC and its corollaries continues with improved instrumentation.

Electrostatic Manipulation of Level of Bulk Liquid for Studies of Saturated Superfluid 3He Films

In studies of saturated superfluid helium films, the level of bulk liquid is an important parameter in determining the thickness of the film. To change the level at low temperatures, a complicated system with a bellows and an extra fill line is usually needed. In this paper, we report a simple device that can be used to change the level using an electrostatic force. This level controller consists of a stack of 60 silver plates of 0.1 mm thickness, separated from each other by a 0.1 mm gap. The application of a dc voltage V to every other plate pulls the dielectric liquid 3He into the gaps, resulting in the drop of the bulk level. The change in level is in agreement with that expected by the balance between the electrostatic force and gravity, and the decrease is as large as 0.27 mm at V=200 V. The level controller is also used to detect the superfluid transition of bulk liquid 3He through the sudden reduction of the response time after V is varied.

Superfluid Transition of a 4He Thin Film Pressurized by Bulk Liquid 3He

We measured transverse acoustic impedance Z of normal fluid 3He at 46.6 MHz on a surface coated with a thin 4He film. The real component of the impedance, Z′, in the coated samples deviates from Z′ in the pure 3He in the low temperature region. Z′ on the coated samples is almost identical with Z′ in the pure sample at high temperature and gradually deviates below a particular temperature T onset . T onset is possibly the superfluid onset temperature of the 4He film pressurized by the bulk liquid 3He. The gradual decrease in Z′ means that the superfluid component in 4He film increases gradually, which is expected from the dynamic KT transition at high frequency. The thicker is the film, the higher is the T onset . The range of T onset we observed was between 40 and 160 mK. This is much lower than that at the saturated vapor pressure. Suppression of T onset achieved by the applied pressure from bulk liquid 3He was presumably caused by the dissolved 3He in the film, thickening of the inert layers and/or by the strong correlation effect. The result shows that the specularity of 3He quasiparticle scattering is strongly affected by superfluidity of the 4He film.

Large Boundary Magnetism and Superfluidity of Liquid 3He in Nanometer-sized Porous Alumina

Continuous-wave NMR measurements were performed for liquid 3He in porous alumina with nominal pore size of 20 nm in diameter, at temperatures down to 0.3 mK. The signal is composed of two contributions: from the liquid and from the boundary solid layer of 3He on the alumina’s surface. The latter shows a well-known ferromagnetic tendency and signal intensities can be fitted to a Curie-Weiss law in the high temperature region. The obtained Weiss temperatures are 0.18 and 0.50 mK at 7.5 and 28 bar, respectively. 4He coverage (4 monolayers) completely eliminates boundary signal between 7.5 bar and 32.5 bar. The residual liquid signal shows frequency shift and broadening below superfluid transition temperatures depending on liquid pressures. The obtained P-T phase diagram well resembles that of bulk liquid 3He in spite of the very narrow pore-size comparable to the coherence length of superfluid 3He.

3He Anomalously High Spin Diffusion in Solid Para-Hydrogen

NMR measurements of 3He spin diffusion coefficient in solid para-H2 are carried out at the temperatures 0.45–1.5 K. The crystals have been grown under constant pressure 20–130 bar. The 3He concentrations in the initial para-H2–3He gas mixtures were 0.1% and 0.3%. It is found out that the decay of echo amplitude vs both magnetic field gradient G and time interval τ between RF pulses is of non-exponential character, typical of one-dimensional diffusion in restricted geometry. The values of true spin-diffusion coefficient DS measured are found to be ∼10−4 cm2/s at 20 bar. At 108 bar DS value is one order of magnitude less. DS does not depend on temperature. Such spin diffusion coefficient values seem to be anomalously high in comparison with well-known values of DS=10−5 cm2/s for bulk liquid 3He at 27 bar and DS=10−8 cm2/s for bulk solid 3He at 108 bar. The special experiments with the crystal annealing make it clear that the high spin diffusion here is connected with fast diffusion along dislocation lines.

Heat Capacity of Adsorbed Helium-3 at Ultra-Low Temperatures

We report on direct measurements of the heat capacity of monolayers of 3He adsorbed on the surface of a copper cell filled with superfluid 3He. We found that at ultra low temperatures the surface 3He heat capacity dominates over the heat capacity of the bulk liquid 3He. The replacement of adsorbed 3He by 4He changes the heat capacity of the sample by an order of magnitude. These investigations were made in the framework of the “ULTIMA” project, a dark matter detector based on superfluid 3He in the limit of ultra low temperatures.

可視化法による液体3Heの沸騰観測

The behaviors of bubble nucleation and growth in liquid 3He were investigated visually using the shadowgraph method. We have constructed two types of cryostats and sample cells for measurements between 0.5 and 1K. The 3He bubble that formed on the heated copper surface was spheroid-like due to a low surface tension and small buoyancy force. The time for required for the bubble to grow and separate from the surface was 14ms at a heat flux of q = 8=10-5 W/cm2 and bulk liquid 3He temperature of 0.7K. This means that the bubble growth rate is high as compared to other low-temperature liquids. The bubble size, number of bubbles separating from the heated surface in a specific time and the rising velocity of the bubbles were analyzed using photographs obtained from a high-speed camera as a function of heat flux and liquid 3He temperature. In the region of large heat flux, large bubbles formed by bubble accumulation covered the copper surface and the increase in bubble number as q increased became insignificant. In this region, the amount of heat flux carried by bubbles as latent vaporization heat was approximately 60% of the applied heat flux. The characteristic heat transfer curve of liquid 3He measured previously by our group could be explained qualitatively by these boiling behaviors.

Microscopic calculations of the dynamic structure factor of bulk liquid 4He

Results of many-body calculations of the dynamic structure factor of bulk liquid 4He in 2D and 3D are presented and analyzed. The problem is reformulated as one of solving equations of motion for the one- and two-body correlations derived from a microscopic Hamiltonian and from a Jastrow-Feenberg wave function with time-dependent correlation functions through the least-action principle. At the first practical level of implementation this reproduces the correlated basis functions (CBF) theory, which gives qualitatively correct low-energy properties. The theory is used to study the anomalous dispersion of low-momentum phonons and the high-momentum behavior of the single-excitation branch near the two-roton continuum.

Finite H 2 concentrations in superfluid 4He

We have studied the solubility of molecular hydrogen in bulk liquid 4He at zero temperature using the diffusion Monte Carlo method and realistic interatomic potentials between the different species of the mixture. Around the 4He equilibrium density, the H 2 molecules clusterize in liquid-like drops blocking the existence of a uniform dilution. On the contrary, at higher densities the cluster formation is less feasible and metastable dilute solutions may exist.

Dynamics of liquid 4He in vycor

Using inelastic neutron scattering, we have observed well-defined phonon-roton ( p-r) excitations in superfluid 4He in Vycor over a wide wave-vector range, 0.3</=Q</=2.15 A(-1). The p-r energies and lifetimes at all temperatures are the same as in bulk liquid 4He. However, the weight of the single p-r component does not scale with the superfluid fraction rho(S)(T)/rho as it does in the bulk. In particular, we observe a p-r excitation above T(c) = 1.952 K, where rho(s)(T) = 0 in Vycor. This suggests, if the p-r excitation intensity scales with the Bose condensate, that there is a separation of the Bose-Einstein condensation temperature and the superfluid transition temperature T(c) of 4He in Vycor.

Energetics, surface tension, and prewetting jump of superfluid 4He films adsorbed on planar substrates

The energetics of superfluid films of 4 He adsorbed on planar substrates is studied. For this purpose, the energy per particle of the systems e is expressed as a polynomial expansion in powers of the inverse of coverage. The surface energy σA and the chemical potential μ, defined according to basic equations of thermodynamics, are written in terms of the proposed expansion. From the expression derived for the third-sound velocity c3 it is possible to estimate the prewetting jump. This formalism is applied for analyzing films adsorbed on alkali metal and H 2 surfaces. For all the examined substrates the determined energy per particle in the limit of films with infinite width, e∞ , is in agreement with the value for bulk liquid 4 He. The surface tensions and prewetting jumps obtained in the present work are compared with results of previous studies.

Giant thermomechanical effect in normal liquid 3He

Measurements are presented of the thermomechanical coefficient of normalliquid 3He confined in a porous plug preplated with four monolayersof 4He. These nonmagnetic monolayers displace the magnetic solid-like3He monolayers that are adjacent to the pore surfaces when the plugis filled with pure 3He. In the low-temperature limit (T &lt;= 10mK) the coefficient can be described by Δ P/Δ T ~ s/6vwhere Δ P is the pressure difference across the plug generated bythe temperature difference Δ T, and s and v are the molarentropy and molar volume. This low-temperature limit corresponds to thecondition d &lt;&lt;lq where d is the pore diameter and lq isthe bulk liquid 3He quasiparticle mean free path; that is, thequasiparticles are predominantly boundary scattered in the pores. Themeasured coefficient is half that calculated by Edwards Culman and He. When compared with this new experimental result for the 4He-platedporous plug, the earlier result for pure liquid 3He is strikinglylarger (by up to 30x at 2~mK). This enhancement is reminiscent ofthe giant thermopowers measured in Kondo and other dilute magneticalloys. It is speculated that the enhanced thermomechanical coefficientfor pure liquid 3He is due to magnetic scattering of the 3Hequasiparticles by the two magnetic solid-like 3He monolayers adjacentto the pore surfaces. PACS Nos.: 67.55.-s and 67.55.Hc

Thermal conductivity and first viscosity via temperature-dependent elementary excitation spectra in thin and bulk liquid 4He

The coefficients of thermal conductivity (ϰ) and first viscosity (η) in thin and bulk liquid 4He are evaluated explicitly as a function of temperature via the zero-temperature and temperature-dependent two- and three-dimensional elementary excitation spectra that are microscopic only in the long-wavelength limit. The coefficients ϰ( T) and η( T) obtained from the temperature-dependent spectrum have slightly larger values than those of the zero-temperature spectrum through the whole range of temperatures, while as the temperature approaches absolute zero, the coefficients ϰ( T) and η( T) coincide with each other in both spectra. Below about 0.8 K, both coefficients increase exponentially with decreasing temperature. At temperatures below about 0.3 K, ϰ( T) in the thin and bulk cases have T -5 and T -6 dependences, respectively, whereas η ph( T) has a T -1 dependence in both dimensions with extra temperature-dependent terms, which originate from three-phonon processes for both excitation spectra.

Two-ripplon processes of electrons on the liquid 4He surface

Effects of two-ripplon processes of electrons on the surface of liquid 4He are examined theoretically. In the derivation of the electron-ripplon interaction, effects of the barrier potential due to bulk liquid 4He are removed exactly by the canonical transformation. The effective interaction Hamiltonian so derived is different from the one used earlier. Calculations of the momentum loss rate and the energy loss rate of warm electrons are performed based on this Hamiltonian, and the momentum and energy loss rates due to the two-ripplon process are smaller by approximately an order of 10 −5 than those due to the one-ripplon process. This is in contrast to the earlier calculations in which the energy loss rate was claimed to be governed by the two-ripplon process.

3He impurities on liquid 4He : From the bulk surface to films

The properties of the system formed by 3He atoms on the surface of the bulk liquid 4He are studied, using a density functional approach. Two types of states are well localized at the surface. Recent experiment by Hallock et al. on magnetization of 3He on 4He films agree with this prediction.

Fermi liquid parameters of a 2D 3He film

Abstract A temperature independent magnetic susceptibility has been observed for the second layer of 3He on graphite for second layer surface densities less than 0.055 A-2, consistent with 2D Fermi liquid behaviour. The Landau parameter Foa is determined using known values of m∗/m. The relative dependence of these two parameters is in good agreement with almost localised Fermion theory, as is the case in bulk liquid 3He.