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We have studied the collective excitation of fractional quantum Hall effect (FQHE) in the rotating Bose-Einstein condensate (BEC) using CF theory at the filling fraction $\nu=1/2$. The roton type of excitation in the FQHE of electron system is established over the years for all the filling fraction, whereas the collective excitation at $\nu=1/2$ filling fraction in the rotating BEC shows no roton minimum. We have investigated this using composite fermion theory with the P$\ddot{o}$schl-Teller interaction potential between the particles. We have seen that the long range interaction will give the roton, whereas short range interaction gives no roton minimum.

We show for the first time high-resolution excitation spectra of bulk superfluid and liquid 4 He obtained in a wide energy range (0–3 meV) in a broad temperature interval 0.6–2.5 K. The experiments were performed at 0.4 bar constant liquid pressure on the time-of-flight crystal analyser neutron spectrometer IRIS at the ISIS Facility. There is a real gap in resolution between neutron spin echo or exact-backscattering spectroscopy and other conventional time-of-flight or triple-axis-spectrometer measurements, which at the moment can only be covered by IRIS. The unique combination of high resolution and wide dynamic range accessible on this inverted geometry spectrometer allowed for a non-conventionally detailed line-shape analysis of the roton excitations and made possible the separation of the roton and the higher-energy broad components. We provide the high-resolution evidence of a remainder single-phonon response at the extrapolated roton energy above T λ . We conclude that the superfluid phase transition manifests itself in the strong slowdown of the variation of the single-phonon line shape with increasing temperature, rather than in the total disappearance of the signal.

We report on a new zero-field spin-echo spectrometer (ZETA), installed at the thermal three-axis spectrometer IN3 at ILL, Grenoble. In this technique the two long precession solenoids from neutron spin echo are replaced by two pairs of magnetic resonance coils in a zero-field region. This allows easy adaptation of tilted field geometries, necessary for measurements of phonon line widths with μeV energy resolution. First test measurements of the roton line width and energy shift as well as line width of the low- Q phonon and in the “region beyond the roton” in superfluid 4 He are described. The results are in agreement with the literature and show the good operation of ZETA. The implementation of ZETA at the high-flux three-axis spectrometer IN20, foreseen in the near future, will increase the count rate by typically one order of magnitude.

An approach is developed that allows to explain the unusual dependence of the electrical resistivity ρ(T) of amorphous alloys on temperature T. Interactions between the free electrons and the longitudinal acoustic excitations in the small-wavelength region (“the roton region”) are shown to cause such a behaviour of ρ(T) at moderately low temperatures. The features of the electron–phonon interactions in an amorphous alloy as compared to the crystal state case are discussed. The theory is illustrated by numerical calculations of the electrical resistivity ρ(T) for Mg–Zn and Cu–Sn amorphous alloys at the different alloy concentrations in the 0 K temperature range. Qualitative agreement between the theory and the experimental data is achieved.

We describe the application of superfluid 3 He at very low temperatures as a highly sensitive bolometer for elementary particles detection. Recently we were able to detect the cosmic muon scattering with energy of 45 KeV . The other important property of superfluid 3 He at very low temperatures is its analogy with quantum vacuum of the Universe. At very rapid superfluid transition in 3 He , follows after a reaction with single neutron, the creation of topological defects (vortices) has been demonstrated in accordance with the Kibble–Zurek scenario for the cosmological analogue. We discuss here the extension of the Kibble–Zurek scenario for the case when alternative symmetries may be broken and different states can be nucleated independently. We have calculated the nucleation probability of the various states of superfluid 3 He during a superfluid transition. The new theory of transition from supercooled A phase to the B phase, triggered by nuclear reaction, have been established. Our theory explains the results of Stanford experiments much better, then well known “Baked Alaska” scenario.

High-resolution measurements of the temperature dependence of the roton lifetime and energy shift in superfluid 4He have been performed using the IN20 thermal neutron triple-axis spectrometer spin-echo option (TASSE). This experiment constitutes the first implementation of the spin-echo technique for inelastic neutron scattering measurements on IN20 using the optimized field-shape superconducting precession coils. An energy resolution of 0.7 μeV was achieved and the results are in agreement with previous studies. The use of additional gradient coils enables to substantially improve the energy and the momentum transfer resolution, and to match excitation dispersion slopes and curvatures. This setup is designed to reach the nano-eV energy resolution in the case of quasi-elastic scattering experiments.

Low-frequency transport properties of the Wigner solid on normal and superfluid 3He have been studied. It is known that the Wigner solid deforms the free surface of liquid He to form a dimple lattice. The low-frequency resistivity is successfully interpreted by the ballistic and specular scattering of 3He quasiparticles from the dimple lattice. The resistivity decreases abruptly below the superfluid transition temperature. For superfluid 3He-A, the l -texture, presumably perpendicularly oriented to the free surface, has an essential influence on the resistivity.

The dependence of electrical resistivity ρ ( T ) on temperature T in a region of moderate temperatures is considered for amorphous simple metals. It is shown within the Faber–Ziman theory that the ratio [ ρ ( T )− ρ (0)]/ T 2 has a maximum in the temperature region 10 K⩽ T ⩽100 K The theory is illustrated by numerical calculations performed for hard-sphere models of amorphous Mg and Zn.

The phonon dispersion curves and the elastic constants are evaluated for crystalline 4 He and 3 He near melting at low temperature in the deep quantal regime. The structures considered are the hexagonal close-packed and the body-centred and face-centred cubic ones for 4 He and the body-centred cubic one for 3 He . The calculations use a density functional approach to construct a field of effective force constants in the strongly anharmonic solid near melting from its Debye–Waller factor and from the linear density response function of the fluid phase at freezing. The results of the calculations are compared with the available experimental evidence: good agreement is generally found for transverse phonon frequencies and shear elastic constants, and phenomenological adjustments of the force-constant field are proposed for a quantitative description of the longitudinal modes. A relationship between the dispersion curves of phonons in crystalline 4 He and that of elementary collective excitations in superfluid 4 He is displayed and discussed in the light of current interpretations of atomic dynamics in the superfluid phase, with main emphasis on the region of the roton minimum.

We report the results of first experimental and theoretical studies of two-dimensional (2D) Wigner solid (WS) motion on the free surface of normal and superfluid 3 He, at ultra-low temperatures down to 0.24 mK. It is shown that the WS transport is determined thoroughly by the bulk Fermi-quasiparticle scattering at the surface dimple sublattice produced by localized electrons. Besides interesting electronic properties of the system, the 2D WS serves as a powerful probe for the bulk properties of superfluid 3 He.

Inelastic neutron scattering measurements of the roton in superfluid helium confined in two different porosity aerogels are presented. The temperature dependence of the roton energy exhibits an anomalous crossover behavior at T c = 1.9 K. Below T c the roton energy is found to be weakly temperature dependent while above T c it is very strongly temperature dependent. The roton lifetime for the confined liquid also display a weak crossover behavior. A simple qualitative model for this behavior in terms of a confined length scale is discussed.

We determine the behavior of the excitations in liquid 4He, covering the normal and superfluid phases, for a range of temperatures (1 0.1 A −1 ) and pressures (0

The energy of the magneto-roton minimum has been measured by non-equilibrium phonon absorption in high mobility electron and hole gases. In the electron gas the measured energy gap is in good agreement with theoretical values. In the hole gas the values are lower than a simple theory would suggest. The most likely cause is Landau level mixing.

The translational motion of a microsphere (radius 100 μm) in liquid helium is investigated. The sphere is levitating inside a superconducting capacitor and oscillates about its equilibrium position. The velocity amplitude and the resonance frequency are measured as a function of driving force and temperature (0.35 K up to 2.2 K). By increasing the driving force we first find a linear regime (laminar flow) which changes abruptly into a nonlinear one (turbulent flow). For temperatures below 0.7 K the linear drag is given by ballistic roton and phonon scattering whereas for temperatures above 1.1 K the hydrodynamic force on the sphere is described by Stoke's solution. In the turbulent regime, above a temperature independent threshold velocity, we find the drag force to be given by turbulence in the superfluid component plus an essentially laminar drag by the normal component.

The possibility of the existence of a weak peak (connected with ‘one-atom’ scattering) in the dynamic structure factor of superfluid helium is shown. We found such a peak on the basis of the dielectric formalism in a weakly non-ideal Bose-gas at low temperatures. The Landau condition of superfluidity is fulfilled due to strong damping for this region of frequencies.

A review is given on the effect of a stationary heat current Q on the superfluid transition of 4He in the linear and nonlinear response regime. Results on various static and dynamic quantities as derived by the renormalization- group theory are discussed. This includes the temperature profile, the thermal bulk and boundary resistance, the interface between normal-liquid and superfluid 4He, the depression of Tλ, the superfluid density, second sound and the specific heat at finite Q.

Starting from an accurate representation of the wave function of the ground state and of the phonon-roton excitations based upon the shadow function we present a microscopic density matrix for superfluid 4 He. The roton and maxon energy is computed both at zero and at finite temperature at different densities. The separate contributions of kinetic and potential energy of the roton excitation are computed and we find that a roton lowers the potential energy. The roton contribution to the depletion of the Bose-Einstein condensate n 0 is computed. Excitation of 5 to 10 rotons is needed for the depletion of one atom from the condensate and no simple relation is found between the T dependence of n 0 and of g ( r ). Other quantities we compute as function of T are the static structure factor and the strength of the ‘one-photon’ peak of the dynamical structure factor. Comparison of our results with experiment gives some evidence that additional excitations become important above about 2 K.

Using third sound, we have found that helium atoms can form a superfluid in direct contact with the crystalline surface of solid hydrogen. An anomalous phase marked by a second line of transitions similar to the Kosterlitz-Thouless transition has also been discovered for thin superfluid films on the H2 substrate for T

Density and spin fluctuations in liquid 3 He and 3 He- 4 He mixtures have been studied by neutron inelastic scattering. We discuss the similarities between the density fluctuations in normal liquid 3 He and superfluid 4 He (anomalous dispersion and the ‘roton minimum’ that reflects the local order) as well as damping mechanisms that could explain the large width of the 3 He zero-sound mode. A line-shape analysis shows that existing theories cannot describe the spin fluctuations observed in liquid 3 He. In 3 He- 4 He mixtures, the shift and broadening of the phonon-roton mode is critically analyzed in terms of Landau damping. The 3 He quasiparticle dispersion, and therefore the effective mass, obtained from neutron scattering measurements on 3 He- 4 He mixtures, shows a clear temperature dependence. Although this is in contrast to what is normally assumed, the specific heat calculated from this dispersion is in excellent agreement with thermodynamic measurements.

The far-infrared magneto-optical properties of remotely doped wide-parabolically graded AlGaAs quantum wells is reviewed. The optical response of the system is the same as that of a single-component three-dimensional plasma. Extensive studies were made of the plasma-shifted cyclotron resonance in the Voigt geometry. It is shown that the resonance frequency is independent of the areal density which demonstrates the generalized Kohn theorem. The internal modes of the system are excited by using wells with periodic and aperiodic perturbations superimposed on the parabolic potential. Dimensional modes and grating modes are identified which permit the wave-vector assignment of the internal magneto-plasma oscillations. From results on different samples and magnetic fields the dispersion relation for magneto-plasmons is measured. A roton excitation is observed at q ⋍2/ l 0 which is good agreement with the predictions of calculations based on the single-mode approximation.

We present a new description of the quasiparticle spectrum of superfluid 4He based on the assumption that in addition to the density excitations proposed by Feynman, there exist localized modes that represent elementary vortex-cores. The energy spectrum which results from the hybridization of these two kinds of excitations is compared to the experimental data. A second branch of excitations interpreted as a quantized vortex-loop is obtained whose energy agrees with critical velocity experiments.

Phonon-roton states, energetical low-lying dynamic anomalies at wave vectors Qp in the phonon dispersion of disordered systems, can get excited thermally as well as by inelastic electron scattering. The latter should be effective whenever the diameter of the Fermi sphere matches Qp. Therefore, in addition to the elastic umklapp scattering of electrons on the static structure which exists already at low temperature, above a characteristic temperature T0 the electrons can undertake inelastic umklapp scattering on the phonon-roton states. Additional deviations to the free-electron behaviour arise causing a knee in the thermopower and an inflection point in the resistivity at T0. Measuring these anomalies versus composition, we are able to reveal the concentration dependence of T0 which approaches zero temperature for those alloys with 1.8 electrons per atom.

We report high-resolution high-precision measurements of S ( Q , ω ) of liquid 4 He at SVP at a range of temperatures above and below T λ , covering the wave vector range from 0.3 to 2.1A -1 . The temperature dependence is seen to depend sensitively on Q , the phonon remaining a well-defined excitation above T λ , while the maxon and roton excitations change abruptly at T λ , leaving no sharp peak at temperatures above.

Using Landau's theory of elementary excitations together with a simple model for the interactions between excitations, we calculate the thermodynamic properties of superfluid helium-4 at pressures below the saturated vapor pressure and above the normal freezing temperature.

The solidification model for superfluid 4 He is reviewed, where the symmetry breaking order parameter η is appropriately defined and included in addition to the density change ξ. As a remarkable feature, the model explicitly shows that the instability to the solid is associated with the instability against the fluctuation of η, namely the softening of ‘hyperbolic roton’. The rate W of solid nucleation is calculated based on the model. In contrast to ξ, η is nonconserved quantity, and then it leads the novel exponents in W near the spinodal pressure.

We propose a simple phenomenological model for dissipative dynamics of a superfluid. Qualitative agreement between the results of our numerical calculations and of the experiment on a superfluid helium three weak link system gives strong support for our model.

By employing an interdigitated capacitor (IC), we searched for ∼10 μm wavelength surface waves on superfluid 3He films. We have not observed such waves yet, possibly because the damping is still too large. Making use of the IC, the film flow was observed in normal and superfluid 3He.

Phase transitions in superfluid Fermi-liquid (FL) from one-gap superfluid state to two-gap state have been studied. The systems of fermions of one and two (nuclear matter) sorts are considered. The temperature and density dependences of the order parameters for new two-gap solutions of the self-consistent equations are determined.

We extend the theory of Sobnack and Inkson (Phys. Rev. Lett. 82 (1999) 3657) by including roton backflow semi-phenomenologically in the form of a backflow potential to examine the effect of backflow on the quantum evaporation of atoms from superfluid helium by rotons. We solve the resulting equations numerically and calculate the probabilities P ra of atom (a) emission by both R + and the negative group velocity R − rotons (r). We compare the results with the corresponding efficiencies when backflow is neglected and we comment on the improved agreement with experiments.

The pressure dependence of the nonlinearity coefficient α of the roton second sound in superfluid He-II at pressures up to 25 bar has been studied. It has been found that with increasing pressure the temperature Tα, at which the coefficient α goes through zero, is lowered from 1.88 to 1.58 K. It means that at all pressures up to the freezing of the superfluid liquid there exists a wide range of temperatures Tα

We report on our work on nanomechanical resonators. The resonators are machined out of commercial silicon-oninsulator (SOI) material with a covering metal layer having eigenfrequencies in the radio frequency (RF) regime. At higher oscillating amplitudes they are driven into nonlinear response. The properties of the nonlinear resonators can be used for charge detection. Furthermore, we report on "rst experiments on using these resonators for exciting phonon and roton modes in 4He. ( 2000 Elsevier Science B.V. All rights reserved.

The nature of elementary thermal excitations in high-T c superconductors is considered in view of the fact that the phase transition at T c and a few degrees below has been shown to have the same universality class as the XY model and the helium λ-transition. Those transitions have been shown to be driven by thermally excited vortex loops, and the smallest loops excited at low temperatures have been identified as the roton excitations of superfluid helium. The analogous excitations in high-T c materials were first recognized by Friedel, being the smallest vortex loops with diameters determined by the coherence length and the CuO plane spacing. Near T c longer loops are excited, made up of parallel and perpendicular vortex segments that are elliptical in shape below T c , but which become circular at T c as the anisotropy becomes irrelevant. These loops may provide a simple explanation of infrared reflectivity results, where an excitation was observed whose energy remained finite as T c was approached, while the superfluid conducting fraction in the planes dropped smoothly to zero. This is precisely the same behavior observed in liquid helium, where the energy of the smallest loops (the rotons) is unrenormalized and remains finite at T λ , whereas the superfluid density is driven smoothly to zero by the largest loops.

A simple phenomenological scheme has been applied to the Cornell data so as to shed more light on the excitations in the 3 He-He II sandwich system. In this context a new expression for the normal density of the system as a function of the temperature has been derived. New values have thereby been obtained for the roton gap and the speed of first sound for the 4 He-component, as well as for the effective mass of the 3 He-component. Tentative information about possible 3 He clusters has also been extracted.

Results for the temperature dependence of the inelastic neutron scattering at the roton wavevector, q=2.0A˚-1, in liquid4He at a constant density of 0.1715 g·cm-3 are presented. The superfluid transition temperature, Tλ=1.9202±0.0002K (at P=20.05 bar), is approached to within 0.0026 K (0.014 K) from below (above). Analysis in terms of the relaxation function ν-1χ″(q, ν) shows that, as Tλ is approached from below, there is an increasingly rapid decrease (increase) in the roton propagation frequency (intrinsic width). This “softening” is complete at Tλ where there is a collapse to the non-propagating behavior (central modes only) characteristic of ordinary fluids.

Stimulated by recent high-resolution neutron data from ILL, we have carried out an extensive numerical study of the single-particle ϱ 1 ( Q , ω) and the two-particle ϱ 2 ( Q , ω) spectral densities within the well known Ruvalds and Zawadowski (ZS) scenario, over a wide range of wavevectors (1≲Q≲3A˚ -1 ), frequencies and temperatures. We extend the original RZ analysis (which concentrated on the two-roton spectrum) to include the multiparticle structure associated with the maxon-roton and maxon-maxon spectra. The microscopic theory of a Bose-condensed fluid shows that S ( Q , ω) involves a weighted sum of ϱ 1 ( Q , ω) and ϱ 2 ( Q , ω). As a result, multiparticle structure exhibited by S ( Q , ω) is not easily related to theoretical results for ϱ 1 ( Q , ω) and ϱ 2 ( Q , ω).

By generalizing an approach due to Leggett, we develop a new method of calculating the superfluid density in spatially inhomogeneous superfluid systems in two and three dimensions. In case of small non-uniformities in the density, the superfluid density is expressed in terms of the density response function for the homogeneous system and the strength of the external potential. The potential strength may be estimated from the effective mass. For real4He we use the Bogoliubov inequality relating the static structure factor to the density response function and Monte Carlo results for the static structure factor to give approximate upper bounds for the superfluid density. We apply our theory to4He films on solid hydrogen.

A new formalism will be proposed for the Raman scattering from He-II near the two-roton threshold by noting that the processes including long wave-length photons dominate the intermediate states, thus being automatically free from the difficulty of the hard-core problem with which the conventional theories were unable to cope. The resulted expression for the intensity is proportional to the multi-phonon part of the structure factor. By expanding the atomic density fluctuation in terms of phonon-roton operators, Hamiltonian for the elementary excitations is constructed and the structure factor is shown to be proportional to the generalized density of states of interacting rotons: It contains the form-factor of a roton-pair creation from the atomic density at every vertex of the ladder processes as well as at the places where the pair is created and annihilated by light quanta. Assuming a power-law in energy for the form-factor the Raman spectra at various pressures are analysed by taking the coupling constant, g, and the roton minimum energy, Δ, as fitting parameters. The allowed margin for the power of the form-factor, α, is found to be 0≤α≲9/16, including both the conventional case (α=0) and the margin set by the direct roton-roton scattering (α≈1/2), thereby solving the long withstanding puzzle why the theories in error are so successful in explaining the Raman feature. The present theory revived the robust concept of roton bound states at low pressures as well as opened the way to determine Δ, the fundamental quantity of the elementary excitations by Raman data alone.

An experiment to measure P 23 , the probability for Andreev reflection of rotons at the free surface, gives the upper limit P 23 ≤P 24 2 , where P 24 is the probability of single-particle conversion of an R - roton to an atom.

A phenomenological conjecture for a microscopic theory of 4 He is proposed. It is proposed that the quasiparticle excitations are fermion-like with a “fermi surface” in the normal state and that the superfluid state is a bound state of the fermionic quasiparticle pairs, with an energy gap opened up at the “fermi surface”. It is pointed out that once this conjecture is made, many puzzling experimental properties in both the normal and the superfluid state of 4 He can be explained consistently.

We report on our first recent measurements of the energy spectrum of upscattered Ultra-Cold-Neutrons in liquid He4 at temperatures around 1 Kelvin. The measurements were made on the Superthermal UCN Source at the ILL [1]. This source produces UCN’s in liquid He4 by down-scattering (phonon-emission) of 10 A neutrons. The UCN’s produced in this way are stored in the He4 container, since they are totally reflected from the walls. The UCN’s can gain energy through scattering by Phonons [3] and Rotons [3], and hence leave the container. We have measured the spectrum of these upscattered neutrons by using a pseudo statistical chopper [4]. The first preliminary measurements show a discrepancy with the spectrum expected on the basis of phonon and roton scattering.

Glyde and Griffin have recently given a new interpretation of the quasiparticle dispersion relation for superfluid 4He. The low Q phonon peak in S(ovrarr|Q,ω) corresponds to a zero sound mode while the high Q maxon-roton peak is a strongly-renormalized single particle excitation. We propose that Z(Q) should be viewed as the superposition of the weights of zero sound and maxon-roton excitations. We also speculate that the ratio Z(maxon)/Z(roton) may reflect the value of the condensate fraction n0.

We are measuring the boundary between the superfluid A and B phases of 3He as a function of magnetic field and pressure. The results yield new information on Landau-Ginzburg parameters, microscopic quasiparticle scattering amplitudes, superfluid specific heats, and potentially other normal liquid properties through comparison with models of the superfluid.

2-roton Raman spectra of superfluid 4 He have been measured at T=0.65K under pressures from svp to P=20kg/cm 2 . No intrinsic spectral width has been observed at all pressures. Contribution of phonons has been found in the lower energy region of the 2-roton peak. Considering it, the experimental spectra were compared with the theory by Iwamoto and Ruvalds-Zawadowski (IRZ model). A good fit of the experimental result to the theory has been observed for the svp spectrum. However, similar analysis of the spectrum at 20kg/cm2 has not given a good fit.

Temperature dependence of the Raman spectrum of liquid 411e at a pressure of 5 kg/cm2 has been measured in the temperature region from 0.65 to 3.75 K. The temperature dependence has been found to be described by the one-component model with lorentzian temperature-broadening both above and below the lambda temperature T λ . From the analysis, temperature dependence of the minimum energy and the lifetime of rotons have been determined. The roton energy shows weak temperature dependence, and the lifetime deviates from the Landau-Khalatnikov theory above 1.80 K.

We have measured the specific heat of hydrogen inside the small pores of Vycor glass at temperatures extending down to 4K. The latent heat associated with freezing when cooling, and with melting when warming, is clearly seen. When this latent heat is compared with that of bulk hydrogen it appears that only a fraction of the hydrogen inside our pores takes part in the solid-liquid transition. Furthermore the specific heat measured at temperatures below the latent heat anomaly is clearly much larger than the specific heat of the bulk solid phase. It is also much larger than the T 2 specific heat expected for the monolayer of hydrogen next to the glass wall. If the large specific heat is due to phonon modes, they are unusually soft. It it interesting that the data also fit a roton-type specific heat, with a roton gap of about 23K.

The dynamical structure factors S(k, ω) at k=0.8A −1 from 1.4K to T λ are calculated on the basis of two-fluid dynamical approach,taking rotons as thermal excitations into account. The obtained S(k, ω) have spectra of Lorentzian type whose resonance energy has weak temperature dependence and width is narrower than inverse roton life time.

The principal objectives of the paper are (i) to clarify the two-fluid picture of superfluid 4He by distinguishing and analysing the London-Tisza and Landau two-fluid models, (ii) to present a new derivation of the two-fluid equations within the framework of the Landau model by starting from Hamilton's variational principle in Lagrange form, and (iii) to critically discuss some generally accepted notions concerning momentum densities in the two-fluid models after characterizing the effective mass of the elementary excitations. It turns out that the effective mass density m∗ of the elementary excitations is determined by m ∗ = ρρ n /ρ s . The superfluid velocity vs is shown to allow a dynamic, but not a kinematic interpretation in the Landau two-fluid model.

It is demonstrated that a simple, “one-dimensional” balance equation for the superfluid vorticity can already account for the occurence of the various types of nonuniform distributions of superfluid turbulence observed in capillary flow of helium II. Expressions for the rates of creation and annihilation of superfluid vortices similar to those suggested by Vinen for the case of thermal counterflow would already be adequate.