Superfluid 4He Research Articles

Temperature Dependence of the Order Parameter of the Polar Phase of Liquid 3He in a Nematic Aerogel

It is proved that in the polar phase of superfluid 3He stabilized by a nematic aerogel the temperature dependence of the gap in the spectrum of Fermi excitations must be the same as that in the bulk polar phase without foreign impurities when the liquid quasiparticles are specularly reflected from the aerogel strands. The analogy with the Anderson theorem for conventional superconductors is discussed.

Spherically symmetric formation of localized vortex tangle around a heat source in superfluid He4

We study the dynamical process of the vortex tangle development under a spherically symmetric thermal counterflow around a heat source submerged into a bulk superfluid 4He. We reveal a peculiar vortex dynamics that is unique to this geometry, which is greatly diverse from the vortex dynamics in a homogeneous counterflow. Two types of heater are considered here, namely, a spherical heater with a solid wall and a point-like heater. In both cases, a spherical vortex tangle is formed surrounding the heater. The mechanism of vortex tangle development in the vicinity of a solid wall is strongly governed by Donnelly-Glaberson instability; while, far away from the heater or around a point heater, the mechanism is governed by the dynamics of polarized vortex loops in radial counterflow. The decay process of such localized vortex tangles is also investigated and is compared with that of homogeneous vortex tangles.

Dynamics of turbulent plugs in a superfluid He4 channel counterflow

Quantum turbulence in superfluid He-4 in narrow channels often takes the form of moving localized vortex tangles. Such tangles, called turbulent plugs, also serve as building blocks of quantum turbulence in wider channels. We report on a numerical study of various aspects of the dynamics and structure of turbulent plugs in a wide range of governing parameters. The unrestricted growth of the tangle in a long channel provides a unique view on a natural tangle structure including superfluid motion at many scales. We argue that the edges of the plugs propagate as turbulent fronts, following the advection-diffusion-reaction dynamics. This analysis shows that the dynamics of the two edges of the tangle have distinctly different nature. We provide an analytic solution of the equation of motion for the fronts that define their shape, velocities and effective diffusivity, and analyze these parameters for various flow conditions.

Matchmaking Between Condensed Matter and Quantum Foundations, and Other Stories: My Six Decades in Physics

I present some rather selective reminiscences of my long career in physics, from my doctoral work to the present. I do not spend time on topics such as the nuclear magnetic resonance behavior of 3He, as I have reviewed the history extensively elsewhere, but rather concentrate, first, on my long-running project to make condensed matter physics relevant to questions in the foundations of quantum mechanics, and second, on various rather “quirky” problems such as an attempt to amplify the effects of the parity violation due to the weak interaction to a macroscopic level, and an unconventional proposal for the mechanism of the first-order phase transition between the A and B phases of superfluid liquid 3He.

An experimental study of turbulent vortex rings in superfluid 4He

Macroscopic vortex rings are generated thermally in superfluid 4He, between 1.28 and 1.95 K, by applying a brief voltage pulse to a resistive heater located below a circular vertical tube 5 mm in diameter and 20 mm high. The rings form above the tube and propagate upward with velocities of the order of , resulting in Reynolds numbers up to . We visualize their cross-section, of size comparable with the tube diameter, by capturing the motions of relatively small solid deuterium particles, previously dispersed in the quiescent bath of superfluid 4He. We employ particle positions and velocities to compute the Lagrangian pseudovorticity, which can be seen as a measure of the ring strength and which allows us to identify and track these objects. We thus obtain time-dependent sizes, positions and velocities of the vortex rings. We show that, in the range of investigated parameters, these rings behave as if they were turbulent vortex rings moving in classical viscous fluids, at least in the direction of ring propagation. The outcome reinforces the view that the study of turbulent flows of superfluid 4He is not only interesting in its own right, but that it can also contribute to our current understanding of fluid turbulence in general.

Light Dark Matter and Superfluid He-4 from EFT

We study the response of a He-4 detector to the interaction of sub-GeV dark matter using an effective field theory for the superfluid. We compute the lifetime of the phonon, which agrees with what known from standard techniques, hence providing an important check of the effective field theory. We then study the process of emission of two phonons, and show how its rate is much more suppressed than the phase space expectations; this is a consequence of the conservation of the current associated to the superfluid symmetries.Talk presented at the TAUP 2019 conference.

Possible Thermodynamical Phase Slips in Superfluid 4He Confined in a 2.5-nm Channel of FSM

We have measured the superfluid response of 4He confined in a 2.5-nm channel and have compared with that of 4He in a 2.8-nm channel. In the 2.5-nm channel, the superfluid growth is gradual regardless of areal density and pressure. In contrast, 4He in a 2.8-nm channel shows a sharp superfluid onset at low pressure, although it shows a gradual temperature dependence with increasing pressure. The gradual temperature dependence in both channels is well fitted to the function of static superfluid density based on the Tomonaga–Luttinger liquid model. It indicates that the thermal excitation of phase slips plays an important role in the observed superfluid response.

Dark matter, dark photon and superfluid He-4 from effective field theory

We consider a model of sub-GeV dark matter whose interaction with the Standard Model is mediated by a new vector boson (the dark photon) which couples kinetically to the photon. We describe the possibility of constraining such a model using a superfluid He-4 detector, by means of an effective theory for the description of the superfluid phonon. We find that such a detector could provide bounds that are competitive with other direct detection experiments only for ultralight vector mediator, in agreement with previous studies. As a byproduct we also present, for the first time, the low-energy effective field theory for the interaction between photons and phonons.

Instability of a vortex ring due to toroidal normal fluid flow in superfluid 4He

Vortex rings self-propelling in superfluid 4He are shown to be driven unstable by a toroidal normal fluid flow. This instability has qualitative similarities with the Donnelly-Glaberson instability of Kelvin waves on a vortex filament driven by the normal fluid flow along the vortex filament.

Dissipation mechanisms of tuning fork vibrations in superfluid 3He–4He solutions

The amplitude–frequency characteristics of tuning forks immersed in superfluid 3He–4He solutions were measured in the temperature range of 0.1–2.5 K. The tuning fork resonance frequency and the resonance width were measured as functions of temperature for 5% and 15% concentrations of 3He and, for comparison, for pure 4He. The experimental results for the key dissipation mechanisms, that is, viscous friction and first and second-sound emission of a tuning fork, were analyzed. For separation and evaluation of the contributions of viscous damping and first and second-sound waves, “closed” (in a factory capsule) and “open” (without a capsule) tuning forks were used. The resonance width, which is a measure of dissipation of tuning fork vibrations, was found to be higher in solutions than in pure 4He, and to increase with increasing 3He concentration. It was shown that the existing analytical expression for the contribution of viscous friction provides a good description of the experimental data for 4He only in the hydrodynamic region. For the solutions, the viscosity contribution is consistent with the experiment only at high temperatures (above 1.4 K). For the “open” tuning fork, the contribution of the first-sound is consistent with the calculation results only for 4He, whereas for the solutions, the calculated values are underestimated compared to the experiment. The possible contribution of the second-sound to the dissipation of the tuning fork vibrations in solutions was estimated using experiments with the “closed” tuning fork. This contribution was found to vary non-monotonically with a maximum at temperatures of ≈ 0.6–0.8 K. The ratio of the tuning fork energy loss due to the thermal diffusion wave versus the loss due to the radiation flux of the second-sound wave in superfluid solutions was calculated using literature data with an accuracy of 10–3–10–4.

A next-generation inverse-geometry spallation-driven ultracold neutron source

The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an order of magnitude higher than the strongest proposed sources, and around three orders of magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that are currently statistically limited. A novel “Inverse Geometry” design is used with 40 l of superfluid 4He (He-II), which acts as the converter of cold neutrons to UCNs, cooled with state-of-the-art subcooled cryogenic technology to ∼1.6K. Our source design is optimized for a 100 W maximum heat load constraint on the He-II and its vessel. In this paper, we first explore modifying the Lujan Center Mark-3 target for UCN production as a benchmark. In our Inverse Geometry, the spallation target is wrapped symmetrically around the cryogenic UCN converter to permit raster scanning the proton beam over a relatively large volume of tungsten spallation target to reduce the demand on the cooling requirements, which makes it reasonable to assume that water edge-cooling only is sufficient. Our design is refined in several steps to reach a UCN production rate PUCN=2.1×109s−1 under our other restriction of 1MW maximum available proton beam power. We then study the effects of the He-II scattering kernel used as well as reductions in PUCN due to pressurization to reach PUCN=1.8×109s−1. Finally, we provide a design for the UCN extraction system that takes into account the required He-II heat transport properties and implementation of a He-II containment foil that allows UCN transmission. We estimate a total useful UCN current from our source of Ruse≈5×108s−1 from an 18cm diameter guide ∼5m from the source. Under a conservative “no return” (or “single passage”) approximation, this rate can produce an extracted density of >1×104UCNcm−3 in <1000l external experimental volumes with a 58Ni (335neV) cutoff potential.

Superfluid 3He in Squeezed Nematic Aerogel

We present results of nuclear magnetic resonance (NMR) experiments in superfluid 3He in two samples of nematic aerogel consisting of nearly parallel mullite strands. The samples were cut from the same piece of the aerogel, but one of them was squeezed by 30% in the direction transverse to the strands. In both samples the superfluid transition of 3He occurred into the polar phase, where no qualitative difference between NMR properties of 3He in these samples was found. The difference, however, has appeared on further cooling, after the transition to the polar-distorted A phase (PdA phase) with the orbital part of the order parameter in the 2D Larkin-Imry-Ma (LIM) state. In the squeezed sample the 2D LIM state is anisotropic that results in changes in the NMR, which can be used as an additional marker of the PdA phase and have allowed us to measure the value of the anisotropy.

Thermodynamic Properties of Superfluid 3He in a Nematic Aerogel in a Strong Magnetic Field

The thermodynamic properties of the phases appearing in superfluid 3He in a nematic aerogel in a strong magnetic field are considered. The jumps in specific heat and magnetic susceptibility during the phase transitions have been found. The influence of the dipole energy on the previously obtained phase diagram has been estimated. The transverse and longitudinal NMR frequency shifts have been found for the phases under consideration and the superfluid density tensors have been derived in the Ginzburg–Landau limit.

A new cryogenic apparatus to search for the neutron electric dipole moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). This apparatus uses superfluid 4He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized 3He from an Atomic Beam Source injected into the superfluid 4He and transported to the measurement cells where it serves as a co-magnetometer. The superfluid 4He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of 2−3× 10−28 e-cm, with anticipated systematic uncertainties below this level.

Turbulent radial thermal counterflow in the framework of the HVBK model

We apply the coarse-grained Hall-Vinen-Bekarevich-Khalatnikov (HVBK) equations to model the statistically steady-state, turbulent, cylindrically symmetric radial counterflow generated by a moderately large heat flux from the surface of a cylinder immersed in superfluid 4He. We show that a time-independent solution exists only if a spatial non-uniformity of temperature and the dependence on temperature of the thermodynamic properties are accounted for. We demonstrate the formation of a thermal boundary layer whose thickness grows with temperature of the cylinder's surface, and analyze the properties of the flow in the radial direction, including the local average vortex line density.

Multimode probing of superfluid 4He by tuning forks

Flexural mode vibrations of miniature piezoelectric tuning forks (TFs) are known to be highly sensitive to superfluid excitations and quantum turbulence in 3He and 4He quantum fluids, as well as to the elastic properties of solid 4He, complementing studies by large scale torsional resonators. Here, we explore the sensitivity of a TF, capable of simultaneously operating in both the flexural and torsional modes, to excitations in the normal and superfluid 4He. The torsional mode is predominantly sensitive to shear forces at the sensor–fluid interface and much less sensitive to changes in the density of the surrounding fluid when compared to the flexural mode. Although we did not reach the critical velocity for the quantum turbulence onset in the torsional mode, due to its order of magnitude higher frequency and increased acoustic damping, the torsional mode was directly sensitive to fluid excitations, linked to quantum turbulence created by the flexural mode. The combination of two dissimilar modes in a single TF sensor can provide a means to study the details of elementary excitations in quantum liquids and at interfaces between solids and quantum fluid.

Specific Heat of Superfluid 4He: Why Does It Deviate from the T3 Law at Low Temperatures?

The specific heat of superfluid 4He measured with high precision by Greywall [Phys. Rev. B 18, 2127 (1978)] exhibits downward deviations from the expected T3 law below about 200 mK. The behaviors c...

Transient Heat Transfer in Superfluid Helium Cooled Nb<inline-formula> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula>Sn Superconducting Coil Samples

An experimental setup is operational at the Central Cryogenics Laboratory of the European Organization for Nuclear Research to measure the cooling mechanisms of superfluid 4 He (He II) from prepared Rutherford-type superconducting cable stacks to a stagnant He II bath. For novel magnets designed for the so-called high-luminosity large hadron collider upgrade, a segment of a fully impregnated Nb 3 Sn 11T dipole magnet was measured. A dataset on the thermal behavior is presented, with homogeneous heat inputs of up to approximately 4.8 mW cm -3 corresponding to an average steady-state temperature of 3.1 K for the inner layer and 4.0 K for the outer layer when cooled via a 1.9 K He II bath. We discuss the steady state as well as transient behavior observed.

A highly effective superfluid film breaker for high heat-lift 1 K sorption coolers

Closed-cycle single-shot 4He sorption coolers are used to provide cooling below 1 K in a number of mm-wave astronomical receivers. Helium, condensed by a 4 K stage, fills a coldhead; the vapour above the liquid is then driven off by a charcoal sorption pump to reduce the pressure, and hence temperature, of the liquid until thermal equilibrium is reached with the heat load. The coldhead then maintains this equilibrium until the liquid has completely evaporated, at which point the cooler is recycled.Below the λ-transition temperature, the mass transport of superfluid 4He via the thermomechanical effect from the cold head into the pumping tube(s) has been shown to significantly reduce the hold time and cooling power of these systems. We present modelling and experimental demonstration of a mechanically simple and highly effective superfluid film breaker developed for the 1 K sorption cooler currently being used in the QUBIC experiment.

Core-shell quantum dot electron bubbles as exotic ions in superfluid liquid 4He

A number of experiments in superfluid helium-4 over the past fifty years on the mobility of electron bubbles, which are unique quantum dots in the liquid state, revealed the existence of a “fast” ion and other “exotic” negative ions whose origin and structure still remains unresolved. The fast ion has a mobility which is six times that of the well understood single electron bubble and the other ions span a region from the fast ion mobility to that of the electron bubble. The work presented here shows that a net anionic, two electron, core-shell quantum dot could potentially explain these findings and provide direction for new experimental work. The model described is based on the quantum confinement and stabilization of short-lived shape resonances which originate from anti-bonding orbitals.