Dynamical effects in superfluid helium 4 (original) (raw)
arXiv (Cornell University), 2001
One considers the superfluid (SF) state of a Bose liquid with a strong repulsion between bosons, in which at T=0, along with a weak single-particle Bose-Einstein condensate (BEC), there exists an intensive pair coherent condensate (PCC), analogous to the Cooper condensate in a Fermi liquid with an attraction between the fermions. Such a PCC emerges in a system of bosons due to an oscillating sign-changing momentum dependence of the Fourier component of the pair interaction potential, which is characteristic of a certain family of repulsion potentials. In such cases, the Fourier component is negative in some domain of nonzero momentum transfer, which corresponds to an effective attraction. The collective effects of renormalization (``screening'') of the initial interaction lead to a suppression of the repulsion and an enhancement of the effective attraction. It is the ratio of the BEC density to the full density of the liquid n0/nll1n_0/n\ll 1n0/nll1 that is used as a small parameter---unlike in the Bogolyubov theory for a quasi-ideal Bose gas, in which the small parameter is the ratio of the number of supracondensate excitations to the number of particles in an intensive BEC, (n−n0)/n0ll1(n-n_0)/n_0\ll 1(n−n_0)/n_0ll1. A closed system of nonlinear integral equations for the normal and anomalous self-energy parts is obtained, in the framework of a renormalized perturbation theory built on combined hydrodynamic and field variables. In the framework of the hard-spheres model, a spectrum of quasiparticles is obtained, which is in good accordance with the experimental spectrum of elementary excitations in superfluid 4^44He. The question of applicability of the Landau criterion in the absence of quantum vortices is discussed.
Ukrainian Journal of Physics, 2022
Based on the representation of collective variables with the Hermitian form of the Bogolyubov–Zubarev Hamiltonian, a self-consistent oscillator model of the ground state and excited states of a Bose liquid has been proposed. A new method of calculation of anharmonic terms in this Hamiltonian and its interpretation have been presented. The dispersion equation for a collective excitation in superfluid 4He has been obtained in a self-consistent way, where the real and virtual processes of decay of a collective excitation are considered. The end point, which is determined by the threshold of collective excitation's decay into two rotons, of the dispersion curve has been obtained, and it is shown that the dispersion curve strongly depends on the property of its stability. An approach with a structure factor has been realized without use of any fitting parameters. Based on the oscillator model, a new method of self-consistent calculation of the ground-state energy and the density of a...
Theoretical study of the dynamic structure factor of superfluid 4 He
Physical Review B, 2001
We study the dynamic structure factor S(q, ω) of superfluid 4 He at zero temperature in the roton momentum region and beyond using field-theoretical Green's function techniques. We start from the Gavoret-Nozières two-particle propagator and introduce the concept of quasiparticles. We treat the residual (weak) interaction between quasiparticles as being local in coordinate space and weakly energy dependent. Our quasiparticle model explicitly incorporates the Bose-Einstein condensate. A complete formula for the dynamic susceptibility, which is related to S(q, ω), is derived. The structure factor is numerically calculated in a self-consistent way in the special case of a momentum independent interaction between quasiparticles. Results are compared with experiment and other theoretical approaches.
Unconventional superfluid phases and the phase dynamics in spin-orbit-coupled Bose systems
Physical Review A, 2013
We study the phase distribution and its dynamics in spin-orbit coupled two component ultracold Bosons for finite size system. Using an inhomogeneous meanfield analysis we demonstrate how phase distribution evolves as we tune the spin-orbit coupling γ and t, the spin-independent hopping. For t >> γ we find the homogeneous superfluid phase. As we increase γ, differences in the phases of the order parameter grows leading to twisted superfluid phase. For t ∼ γ competing orderings in the phase distribution is seen. At large γ limit a Ferro-Magnetic stripe ordering appears along the diagonal. We explain that this is due to the frustration bought in by the spin-orbit interaction. Isolated vortex formation is also shown to appear. We also investigate the possible collective modes. In deep superfluid regime we derive the equation of motion for the phases following a semi-classical approximation. Imaginary frequencies indicating the damped modes are seen to appear and the dynamics of lowest normal modes are discussed.
The Fulde-Ferrell state in superfluid helium
Zeitschrift für Physik, 1983
The Fulde-Ferrell state in a superfluid 3He-~He II solution is investigated. Starting from its broken symmetry, a relative translation-gauge symmetry, the linearized hydrodynamic equations to lowest order in wave number are presented. To this order, the superfluid current perpendicular to the preferred direction vanishes identically; at the same time, supercurrents generated by a uniform change in temperature or density become possible. The Goldstone mode of the Fulde-Ferrell state is shown to be a propagating spin-temperature-shear wave.
Structural and dynamical properties of superfluid helium: A density-functional approach
Physical Review B, 1995
We present a novel density functional for liquid 4 He, properly accounting for the static response function and the phonon-roton dispersion in the uniform liquid. The functional is used to study both structural and dynamical properties of superfluid helium in various geometries. The equilibrium properties of the free surface, droplets and films at zero temperature are calculated. Our predictions agree closely to the results of ab initio Monte Carlo calculations, when available. The introduction of a phenomenological velocity dependent interaction, which accounts for backflow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.
Superfluid Helium 3: Link between Condensed Matter Physics and Particle Physics
Acta Physica Polonica Series B
The discovery of the superfluid phases of Helium 3 in 1971 opened the door to one of the most fascinating systems known in condensed matter physics. Superfluidity of Helium 3, originating from pair condensation of Helium 3 atoms, turned out to be the ideal testground for many fundamental concepts of modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and their spontaneous breakdown, topological defects, etc. Thereby the superfluid phases of Helium 3 enriched condensed matter physics enormously. In particular, they contributed significantly - and continue to do so - to our understanding of various other physical systems, from heavy fermion and high-Tc superconductors all the way to neutron stars, particle physics, gravity and the early universe. A simple introduction into the basic concepts and questions is presented.
Physica A: Statistical Mechanics and its Applications, 2008
This article presents a phenomenological dynamic phase transition theory -modeling and analysis -for liquid helium-3. We derived two new models, for liquid helium-3 with or without applied field, by introducing three wave functions and using a unified dynamical Ginzburg-Landau model. The analysis of these new models leads to predictions of existence of 1) a unstable region, 2) a new phase C in a narrow region, and 3) switch points of transition types on the coexistence curves near two triple points. It is hoped that these predictions will be useful for designing better physical experiments and lead to better understanding of the physical mechanism of superfluidity.