Liquid 4He Research Articles

Ideal Bose-gas in nonadditive statistics

The paper analyzes an approach to the generalization of the conventional Bose–Einstein statistics based on the nonadditive entropy of Tsallis. A detailed derivation of thermodynamic functions is presented. The calcu-lations are made for the specific heat of two model systems, namely, the ideal three-dimensional gas obeying the nonadditive modification of the Bose–Einstein statistics and the system with linear excitation spectrum at-tempted as a qualitative approximation of liquid 4He thermodynamics.

Nucleation at quantized vortices and the heterogeneous phase separation in supersaturated superfluid 3He–4He liquid mixtures

Supersaturated superfluid 3He–4He liquid mixture, separating into the 3He-concentrated c-phase and 3He-diluted d-phase, represents a unique possibility for studying macroscopic quantum nucleation and quantum phase-separation kinetics in binary mixtures at low temperatures down to absolute zero. One of possible heterogeneous mechanisms for the phase separation of supersaturated d-phase is associated with superfluidity of this phase and with a possible existence of quantized vortices playing a role of nucleation sites for the c-phase of liquid mixture. We analyze the growth dynamics of vortex core filled with the c-phase and determine the temperature behavior of c-phase nucleation rate and the crossover temperature between the classical and quantum nucleation mechanisms.

λ Phase Transition in Horava Gravity

We present another example of superfluid black hole containing λ phase transition in Horava gravity. After studying the extended thermodynamics of general dimensional Horava-Lifshitz AdS black holes, it is found that only the one with spherical horizon in four and five dimensions has λ phase transition, which is a line of (continuous) second-order phase transitions and was famous in the discussion of superfluidity of liquid He4. The “superfluid” black hole phase and “normal” black hole phase are also distinguished. Particularly, six-dimensional Horava-Lifshitz AdS black holes exhibit infinitely many critical points in P-ν plane and the divergent points for specific heat, for which they only contain the “normal” black hole phase and the “superfluid” black hole phase disappears due to the physical temperature constraint; therefore there is no similar phase transition. In more than six dimensions, there is no P-ν critical behavior. After choosing the appropriate ordering field, we study the critical phenomena in different planes of thermodynamical phase space. We also calculate the critical exponents, which are the same as the van der Waals fluid.

Superfluidity of 4He in dense aerogel studied using quartz tuning fork

Superfluid 4He in aerogel is of interest because it has a normal component coupling to gel strand due to viscosity and a superfluid component with zero viscosity. Superfluid helium in aerogel has two sound modes, a slow critical mode and a fast one. In this study, quartz tuning fork was used in order to study acoustic properties of liquid 4He in aerogel with 90% porosity. Two pieces of aerogel were glued on both prongs of quartz tuning fork that had a resonance frequency of 33 kHz. The tuning fork was immersed in liquid 4He from 2 to 20 bar. The resonance frequency increased in the superfluid phase due to decrease in loaded mass. Temperature variation of resonance frequency was explained by that of superfluid density. Superfluid transition in aerogel was 2 mK lower than that without gel. Additional dissipation was observed in the temperature range between 1 K and transition temperature.

Torsional Oscillator Measurements of Liquid 4He Confined in 2.5-nm Channel of FSM

We measured the superfluid response of liquid 4He confined in 2.5-nm channel under low pressure by means of the torsional oscillator to clarify how the superfluid response varies with decreasing channel diameter. In the previous measurements, in the 2.8-nm channel under 0.13 MPa, the superfluid fraction appears at 1.8 K, and then shows a sharp rise at 0.9 K. On the other hand, in the 2.2-nm channel, no sharp rise is observed although the superfluid fraction appears. In the present measurements for 2.5-nm channel, the superfluid appears at around 1.5 K, and then shows a sharp rise at 0.13 K. By comparison, with decreasing channel diameter, the temperature of superfluid appearance is suppressed with gentle acceleration, which is attributable to the suppression of falling into a BEC-like state. In contrast, the temperature of the rise in the superfluid is suppressed drastically compared with that of superfluid appearance, by decreasing the channel diameter from 2.8 to 2.5 nm.

Attractor Bifurcation and Phase Transition for Liquid 4He

Experiments show that the liquid helium-4 has either superfluid phase or solid phase when temperature decreases or the pressure of the system changes. In this paper, we discuss the equations which govern these phase transitions and derive the criterions for these phase changes. Meanwhile, we give related approximate solutions and draw the phase diagram. In addition, we also prove that the liquid helium-4 bifurcates from the trivial solution to an attractor as parameters cross certain critical value. The topological structure of the bifurcated attractor is also illustrated.

Magnetotransport properties of microstructured AlCu2Mn Heusler alloy thin films in the amorphous and crystalline phase

We have studied the resistance, magnetoresistance and Hall effect of AlCu2Mn Heusler alloy thin films prepared by flash evaporation on substrates cooled at 4He liquid temperature. The as-prepared samples were amorphous and were annealed stepwise to induce the transformation to the crystalline phase. The amorphous phase is metastable up to above room temperature and the transition to the crystalline phase was observed by means of resistance measurements. Using transmission electron microscopy, we have determined the structure factor S(K) and the pair correlation function g(r), both results indicate that amorphous AlCu2Mn is an electronic stabilized phase. The X-ray diffraction of the crystallized film shows peaks corresponding to the well ordered L21 phase. The resistance shows a negative temperature coefficient in both phases. The magnetoresistance (MR) is negative in both phases, yet larger in the crystalline state compared to the amorphous one. The magnetic properties were studied further by anomalous Hall effect measurements, which were present in both phases. In the amorphous state, the anomalous Hall effect disappears at temperatures below 175 K and is present up to above room temperature in the case of crystalline AlCu2Mn.

Constraining spacetime nonmetricity with Lorentz-violation methods

In this report, we will give the first constraints on in-matter nonmetricity. We will show how the effective-field-theory (EFT) toolbox developed for the study of Lorentz violation (LV) can be employed for investigations of the “effective LV” background caused by nonmetricity, a geometric object extending the notion of a Riemannian manifold. The idea is to probe for the effects of spacetime nonmetricity sourced by liquid 4He with polarized slow neutrons. We present the first constraints on isotropic and parity-odd nonmetricity components. Further constraints on anisotropic nonmetricity components within this EFT framework may be feasible with proper experimental techniques in the near future.

Spectroscopy of Ba+ ions in liquid 4He

Atomic ions and free electrons embedded in condensed helium play important role in modern research on quantum fluids and solids. Here we present experimental and theoretical study of Ba+ cations immersed in superfluid He. We observe laser-induced fluorescence of Ba+ injected into liquid He from the plasma of radio frequency discharge in He-Ba gas mixture. The structure of trapping site is studied theoretically in the frame of the atomic bubble model making use of ab initio Ba+ - He pair potentials available in the literature. Calculated spectra of the ion are compared with the results of the experiment.

Spin Kinetics of Liquid 3He in Contact with a DyF3 Micropowder at Ferromagnetic Ordering of Dy3+ Ions

The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.67%) and DyF3 (0.33%) micropowders at temperatures of 1.5–3 K has been studied by pulsed nuclear magnetic resonance (NMR). The DyF3 is a dipolar dielectric ferromagnet with the phase transition temperature Tc= 2.55 K, whereas the diamagnetic fluoride LaF3 is a diluting substance for the optimal observation conditions of 3Не NMR in powder pores. The magnetic phase transition in DyF3 is accompanied by a considerable change in the character of fluctuations of the magnetic moments of dysprosium ions, which affect the spin kinetics of 3Не in contact with the substrate. Significant changes in the relaxations rates of the longitudinal and transverse magnetizations of 3Не have been discovered in the region of magnetic ordering of the solid matrix. The technique of studying the static and fluctuating magnetic fields of a solid matrix at low temperatures using liquid 3He as a probe has been proposed.

Unstable plastic deformation of ultrafine-grained copper at 0.5 K

We investigate the relation between the strain-hardening rate and flow instability of polycrystalline Cu–OF deformed by tension at a constant rate in a liquid 3He atmosphere. The microstructure of the ultrafine-grained crystal, obtained by the equal-channel angular hydro-extrusion method, was varied by annealing at recovery and recrystallization temperatures and was monitored by x-ray diffraction. It is shown that that the flow instability, manifesting itself as macroscopic stress serrations on the tension curve, appears at a threshold tension sufficient for activation of a dynamic recovery that leads to a decrease of the strain-hardening coefficient. We discuss the effect of grain size and the initial dislocation density on the evolution of the dislocation structure that determines the scale and the statistical properties of the flow instability in the investigated crystals at low temperature.

Surface Microparticles in Liquid Helium. Quantum Archimedes’ Principle

Deviations from Archimedes’ principle for spherical molecular hydrogen particles with the radius R0 at the surface of 4He liquid helium have been investigated. The classical Archimedes’ principle holds if R0 is larger than the helium capillary length Lcap ≅ 500 μm. In this case, the elevation of a particle above the liquid is h+ ~ R0. At 30 μm Rc. Here, $${R_c} \cong {\left( {\frac{{\hbar c}}{{\rho g}}} \right)^{1/5}} \approx 1$$ , where ħ is Planck’s constant, c is the speed of light, g is the acceleration due to gravity, and ρ is the mass density of helium. For very small particles (R0 < Rc), the distance h_ to the surface of the liquid is independent of their size, h_ = Rc.

Inelastic Neutrino Scattering on Hot Nuclei of Supernova Matter within the Theory of Finite Fermi Systems

The Nozieres–Pines method for describing neutron scattering on a heated Fermi liquid (liquid 3He) is used to calculate cross sections for inelastic neutrino scattering on the isotope 54Fe, which is an element that plays a key role in the cooling of supernovae. The calculation in question is performed on the basis of the the theory of finite Fermi systems with the aid of the DF3-a Fayans energy density functional.

Bose–Einstein condensation and liquid–gas phase transition in strongly interacting matter composed of α particles

Systems of Bose particles with both repulsive and attractive interactions are studied using the Skyrme-like mean-field model. The phase diagram of such systems exhibits two special lines in the chemical potential-temperature plane: one line which represents the first-order liquid–gas phase transition with the critical end point, and another line which represents the onset of Bose–Einstein condensation. The calculations are made for strongly interacting matter composed of α particles. The phase diagram of this matter is qualitatively similar to that observed for the atomic 4He liquid. The sensitivity of the results to the model parameters is studied. For weak interaction coupling, the critical point is located at the Bose-condensation line.

Variational calculations for ground state properties of liquid 3He injected in a carbon nanotube

Liquid 3He injected in a carbon nanotube is of high interests due to different behavior of the liquid helium in the quasi-one-dimensional systems. In this work, a variational approach has been performed to calculate some thermodynamic properties of this quantum system. In order to do so, a single-walled carbon nanotube containing liquid 3He is considered, applying the Lennard-Jones and Stan–Cole potentials for 3He–3He and 3He–C interactions, respectively. Finally the total energy, equation of state and incompressibility of the system have been calculated. Our calculations show the high values for the incompressibility at high densities, especially for high radii.

Constraining spacetime nonmetricity with neutron spin rotation in liquid 4He

General spacetime nonmetricity coupled to neutrons is studied. In this context, it is shown that certain nonmetricity components can generate a rotation of the neutron's spin. Available data on this effect obtained from slow-neutron propagation in liquid helium are used to constrain isotropic nonmetricity components at the level of 10−22 GeV. These results represent the first limit on the nonmetricity ζ(6)2S000 parameter as well as the first measurement of nonmetricity inside matter.

Quantum reflection of antihydrogen from a liquid helium film

We study the quantum reflection of ultracold antihydrogen atoms bouncing on the surface of a liquid helium film. The Casimir-Polder potential and quantum reflection are calculated for different thicknesses of the film supported by different substrates. Antihydrogen can be protected from annihilation for as long as 1.3 s on a bulk of liquid 4He, and 1.7 s for liquid 3He. These large lifetimes open interesting perspectives for spectroscopic measurements of the free fall acceleration of antihydrogen. Variation of the scattering length with the thickness of a film of helium shows interferences which we interpret through a Liouville transformation of the quantum reflection problem.

Observation of dynamic atom-atom correlation in liquid helium in real space

Liquid 4He becomes superfluid and flows without resistance below temperature 2.17 K. Superfluidity has been a subject of intense studies and notable advances were made in elucidating the phenomenon by experiment and theory. Nevertheless, details of the microscopic state, including dynamic atom–atom correlations in the superfluid state, are not fully understood. Here using a technique of neutron dynamic pair-density function (DPDF) analysis we show that 4He atoms in the Bose–Einstein condensate have environment significantly different from uncondensed atoms, with the interatomic distance larger than the average by about 10%, whereas the average structure changes little through the superfluid transition. DPDF peak not seen in the snap-shot pair-density function is found at 2.3 Å, and is interpreted in terms of atomic tunnelling. The real space picture of dynamic atom–atom correlations presented here reveal characteristics of atomic dynamics not recognized so far, compelling yet another look at the phenomenon.

Magnetic Memory from Site Isolated Dy(III) on Silica Materials.

Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy(III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy(III) siloxide complex on partially dehydroxylated silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, “bare” Dy(III) sites bound to the silica surface. During the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence.

Isentropic calculation for thermodynamic properties of polarized liquid 3He by considering the effect of spin-dependent correlation function

Correlations in quantum fluids such as liquid 3He continue to be of high interest to scientists. Based on this prospect, the present work is devoted to study the effects of spin–spin correlation function on the thermodynamic properties of polarized liquid 3He such as pressure, velocity of sound, adiabatic index and adiabatic compressibility along different isentropic paths, using the Lennard–Jones potential and employing the variational approach based on cluster expansion of the energy functional. The inclusion of this correlation improves our previous calculations and leads to good agreements with experimental results.