Resonance excitation of slow rotons: Linewidth

An explanation of an anomalously narrow microwave absorption line in superfluid ⁴He has been proposed. It has been shown that the experimentally observed resonance linewidth agrees with the assumption of parametric excitation of a macroscopic coherent roton state.     

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相似文献   

Supersolid state of matter

We prove that the necessary condition for a solid to be also a superfluid is to have zero-point vacancies, or interstitial atoms, or both, as an integral part of the ground state. As a consequence, in the absence of symmetry between vacancies and interstitials, superfluidity has a zero probability to occur in commensurate solids which break continuous translation symmetry. We discuss recent 4He experiments by Kim and Chan in the context of this theorem, question its bulk supersolid interpretation, and offer an alternative explanation in terms of superfluid interfaces.     

The two-fluid model with superfluid entropy

Summary The two-fluid model of liquid helium is generalized to the case that the superfluid fraction has a small entropy content. We present theoretical arguments in favour of such a small superfluid entropy. In the generalized two-fluid model various sound modes of He II are investigated. In a superleak carrying a persistent current the superfluid entropy leads to a new sound mode which we call sixth sound. The relation between the sixth sound and the superfluid entropy is discussed in detail.     

Dynamic critical behavior near the superfluid transition in 3He-4He mixtures in two loop order

We calculated in two loop order the field theoretic renormalization group functions taking into account the decomposition of the dynamical vertex functions into the static vertex functions and genuine dynamical parts. The observation of this nonperturbative structure simplifies the theoretical expressions obtained by perturbation theory considerably and makes tractable a complete two loop calculation of the critical dynamics near the superfluid transition of 3He-4He mixtures (model F'). As a result, we obtain various transport coefficients, which govern the nonasymptotic and nonuniversal temperature dependence. We also correct long-standing results for the critical dynamics of the superfluid transition in pure 4He (model F) and for the dynamics of structural or magnetic phase transitions (model C).     

Torsional oscillator and synchrotron X-Ray experiments on solid 4He in aerogel

X-ray diffraction experiments show that solid 4He grown in aerogel is highly polycrystalline, with an hcp crystal structure (as in bulk) and a crystallite size of approximately 100 nm. In contrast to the expectation that the highly disordered solid will have a large supersolid fraction, torsional oscillator measurements show a behavior that is strikingly similar to high purity crystals grown from the superfluid phase. The low temperature supersolid fraction is only approximately 3 x 10(-4), and the onset temperature is approximately 100 mK.     

Study of elementary excitations of superfluid4He in silica aerogels

We have studied the elementary excitations of superfluid⁴He in a silica aerogel at 1.8 K and various filling fractions. The results do not show any departure from bulk⁴He behaviour, suggesting that previously observed anomalies in heat capacity and superfluid fraction data could be the effect of a distribution of He I and He II liquids inside pores of different sizes.This article was processed by the author using the LATEX style filepljour2 from Springer-Verlag.     

Gliding for Gold: The Physics of Winter Sports,by Mark Denny

A comparison of the basic properties of the superfluid phases of liquid ³He with those of electrons in Type I superconductors and of bosons in liquid ⁴He reveals their similarity and differences. This is followed by some examples of the liquid crystal and magnetic properties of superfluid ³He and an account of the relationships between the tensor order parameter and the collective modes of the superfluid phases. The article ends with some comments on our present understanding of quantum liquids.     

二分量玻色-爱因斯坦凝聚中的二超流体模型

4He超流体在一定温度下可用二流体模型描述,包括常规流体和超流体两种成分.用这种二流体模型来描述二分量玻色爱因斯坦凝聚时叫做二超流体模型,是从耦合Gross-Pitaevskii方程出发推导得到的.二超流体模型与4He超流体中的二流体模型非常相近.在特定条件下,二超流体中的两个波模行为非常接近4He超流体中二流体模型中...     

Phase diagram of the A and B phases of superfluid 3He in aerogel

We report the first measurements of the A-B phase transition of superfluid 3He confined within 98% silica aerogel in high magnetic fields and low temperatures. A disk of aerogel is attached to a vibrating wire resonator. The resonant frequency yields a measure of the superfluid fraction rho(s)/rho of the 3He within the aerogel. The inferred rho(s)/rho value increases substantially at the A-to- B transition of the confined superfluid, allowing us to map the A-B phase diagram as a function of field and temperature. At 4.8 bars, the B-T transition curve looks very similar to that in bulk with a simple reduction factor of order 0.45 for both transition field and temperature.     

Metastability and superfluid fraction of the A-like and B phases of <Superscript>3</Superscript>He in aerogel in zero magnetic field

We report the low-frequency sound measurements of the metastable A-like (A*) phase of superfluid ³He confined within a 98% open aerogel matrix in zero magnetic field. The second soundlike (slow) mode provides an accurate determination of the superfluid fraction of (and the transition between) the A* and B phases. The A* and B phases exhibit stable coexistence in the presence of disorder, the ratio of their superfluid fractions (ρ _a ^A* /ρ _s ^B ) is much smaller than that of the bulk A and B phases, and argues that the A* and bulk A phases are distinct.     

Casimir forces, surface fluctuations, and thinning of superfluid film

Recent experiments on the wetting of 4He have shown that the film becomes thinner at the lambda transition and in the superfluid phase. The difference in thickness above and below the transition has been attributed to a Casimir interaction which is a consequence of a broken continuous symmetry in the bulk superfluid. However, the observed thinning of the film is larger than can be accounted by this Casimir force. We show that surface fluctuations give rise to an additional force, similar in form but larger in magnitude, which may explain the observations.     

Classical rotational inertia of solid 4He

The observation of reduced rotational inertia in a cell containing solid 4He has been interpreted as evidence for superfluidity of the solid. We propose an alternative explanation: slippage of the solid, due to grain boundary premelting between the solid and dense adsorbed layers at the container wall. We calculate the range of film thickness, and determine the viscosity that will account for the missing rotational inertia. Grain boundary premelting also explains inertial anomalies in an earlier study of solid helium in porous glass and indicates that the liquid is partially superfluid.     

Condensate-free superfluid induced by the frustrated proximity effect

Since the discovery of superfluidity in 4He and Landau's phenomenological theory, the relationship between Bose condensation and superfluidity has been intensely debated. 4He is known by now to be both superfluid and condensed at low temperature, and more generally, in dimension D≥2, all superfluid bosonic models realized in experiments are condensed in their ground state, the most recent example being provided by ultracold bosonic atoms trapped in an optical lattice. In this Letter, it is shown that a 2D gas of bosons which is not condensed at T=0 can be achieved by populating a layer through a frustrated proximity effect from a superfluid reservoir. This condensate-free bosonic fluid is further shown to be a superfluid with incommensurate correlations.     

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.     

Bose-Einstein condensation and thermodynamic functions of 4He film

A monolayer of ⁴He atoms is treated as a system of hard-sphere bosons in a thin film geometry, with a finite thickness. The method of pseudopotential is used to calculate first the energy spectrum, and then the Helmholtz free energy and other thermodynamic functions of the system. It is found that Bose-Einstein condensation exists below a definite temperature. Much like a liquid-gas transition, the boson system displays a high temperature normal phase, a low temperature condensed superfluid phase and coexistence region. In the present treatment, the minimum momentum associated with the finite thickness of monolayer is used as a parameter. We find that the transition temperature is linearly proportional to the density of the ⁴He film. After performing double-tangent construction of the Helmholtz free energy curve we find for the specific heat a rounded peak at the transition temperature, in agreement with recent experiments. The ratio of the superfluid density at the transition point to the transition temperature is found to be essentially a constant.     

The superfluidd transition temperature of a Fermi liquid: 3He and 3He4He mixtures

The superfluid transitions temperature is calculated from the microscopic theory of a Fermi liquid in terms of the Landau parameters and one unknown scale factor. Determining the latter from the observed transition in ³He leads to an estimate that the superfluid transition in ³He⁴He mixtures may be presently observable.     

The 4He condensate: Experiment and theory reconciled

The extremely small values of the condensate fraction in superfluid ⁴He II (of order 1% or less), obtained from inelastic neutron scattering experiments involving large momentum transfers are shown to be consistent with the calculated zero temperature values (of order 10%).     

Thinning of saturated superfluid 4He films during critical and subcritical flow

We report measurements of the thickness of a saturated superfluid ⁴He film under conditions of both critical and subcritical flow. Thinning consistent to within 20% with the predictions of Kontorovich as applied to our apparatus is observed over the temperature range 1.2 < T < 1.6 K. The results appear to rule out critical flow effects as an explanation of Keller's results.     

Superfluidity of 4He in one and three dimensions realized in nanopores

Superfluidity in one and three dimensions has been studied for 4He fluid films adsorbed in nanopores which are straight channels and three-dimensionally connected pores, respectively. We observed the superfluid in one and three dimensions where thermal phonon wavelengths are much longer than the channel diameter and the period of the pore connection, respectively, and found that the superfluid onset depends on the pore connection. In the straight channels, the observed superfluid density disappears at a temperature far below the heat capacity anomaly of the Ginzburg-Landau transition, while in the pores connected in three dimension, the adsorbed 4He films show an evident three-dimensional transition where the superfluid onset occurs at the heat capacity peak.