Presence Of Superflow Research Articles

Flow-induced charge modulation in superfluid atomic fermions loaded into an optical kagome lattice.

We study the superfluid state of atomic fermions in a tunable optical kagome lattice motivated by recent experiments. We show that the imposed superflow induces spatial modulations in the density and order parameter of the pair condensate and leads to a charge modulated superfluid state analogous to a supersolid state. The spatial modulations in the superfluid emerge due to the geometric effect of the kagome lattice that introduces anisotropy in hopping amplitudes of fermion pairs in the presence of superflow. We also study superflow instabilities and find that the critical current limited by the dynamical instability is quite enhanced due to the large density of states associated with the flatband. The charge modulated superfluid state can sustain high temperatures close to the transition temperature that is also enhanced due to the flatband and is therefore realizable in experiments.

Anomalous tunneling of collective excitations and effects of superflow in the polar phase of a spin-1 spinor Bose-Einstein condensate

We investigate tunneling properties of collective modes in the polar phase of a spin-1 spinor Bose-Einstein condensate. This spinor BEC state has two kinds of gapless modes, i.e., Bogoliubov mode and spin-wave. Within the framework of the mean-field theory at T=0, we show that these Goldstone modes exhibit the perfect transmission in the low-energy limit. Their anomalous tunneling behaviors still hold in the presence of superflow, except in the critical current state. In the critical current state, while the tunneling of Bogoliubov mode is accompanied by finite reflection, the spin-wave still exhibit the perfect transmission, unless the strengths of a spin-dependent and spin-independent interactions take the same value.

Kelvin-Helmholtz Instability and Dissipation in a Phase-Separated 3He-4He Liquid Mixture

We study the behavior of the interface between the 3He-concentrated and 3He-dilute phases of a phase-separated 3He-4He liquid mixture in the presence of superflow in the d-phase. The superflow can produce a Kelvin-Helmholtz instability in the system. Here we consider two types of the instability: (i) quantized vortex in the superfluid liquid near the superfluid-normal interface; (ii) tangential flow of the superfluid component with respect to the normal fluid in the direction parallel to the interface. In these cases the Kelvin-Helmholtz instability has a threshold due to the surface tension and acceleration of the liquid in the direction normal to the interface. The acceleration is of centrifugal origin in (i) and gravitational one in (ii). The presence of the threshold results in quite different scales of characteristics distances. The centrifugal acceleration induces a scale of the order of the core radius b of several angstroms. The acceleration of gravity yields a scale of the capillary length ≃ 1.3 mm. In case (i) we obtain an instability of the vortex at a critical distance Rcr = bρd/(ρd − ρc). The vortex should disappear at distances smaller than Rcr. In case (ii) the interface becomes unstable provided the superfluid component flows in the direction tangential to the interface with a velocity exceeding its critical value ∼6.3 cm/s. There appear ripples with the wavelength of the order of the capillary constant. The instability threshold is found to be lower than in the absence of dissipation and independent of the magnitude of dissipation.

Dynamics of vortex nucleation by rapid thermal quench

By numerical and analytical studies of the time-dependent Ginzburg-Landau model we show that vortex nucleation in superfluid ${}^{3}\mathrm{He}$ by rapid thermal quench in the presence of superflow is dominated by a transverse instability of the moving normal-superfluid interface. The instability threshold is found analytically as a function of supercurrent density and the front velocity. The dynamics of vortex evolution at long times after the quench is investigated.

Nucleation of vortices in superfluid 3He–B by thermal quench

We show that nucleation of vortex loops in superfluid 3He by rapid thermal quench in the presence of superflow is dominated by a transverse instability of the moving normal–superfluid interface. Exact expressions for the instability threshold as a function of supercurrent density and the front velocity are found. The results are verified by numerical solution of the Ginzburg–Landau equation.

Nucleation of Vortices by Rapid Thermal Quench

We show that vortex nucleation in superfluid $^3$He by rapid thermal quench in the presence of superflow is dominated by a transverse instability of the moving normal-superfluid interface. Exact expressions for the instability threshold as a function of supercurrent density and the front velocity are found. The results are verified by numerical solution of the Ginzburg-Landau equation.

Current-carrying state in a polar-phase superconductor at T=0.

We discuss the current-carrying state in a polar-phase superconductor at zero temperature. This phase has a line of nodes on the Fermi surface, and its properties are quite anisotropic. We compute the relation between J and ${\mathrm{v}}_{s}$ both for a pure metal and for one with impurities. This allows us to find the critical current for a variety of situations. We also consider the density of states in the presence of superflow.

New texture with flow in 3He-A.

The textures of $^{3}\mathrm{He}$-$B$ in the presence of superflow in zero magnetic field are investigated numerically. A dynamic texture of domains is found at high flow rates. Within a domain the texture is essentially aligned parallel or antiparallel to the flow. Dissipative precessional motion occurs within localized domain walls. This texture may help to explain recent experimental results which are apparently in conflict with previous theory.

Temperature gradient along superfluidHe4films in the presence of superflow

We have measured the nonlinear thermal conductance of a thin film of $^{4}\mathrm{He}$ as a function of temperature and heater power for a fixed film thickness. When heat transfer through the gas is included we obtain a qualitative understanding of the data in terms of Kosterlitz-Thouless theory as extended to finite superflow by Ambegaokar et al. The exponent in the power law relating conductance and heater power exhibits the universal jump at ${T}_{c}$ predicted by its simple relationship to the areal superfluid density.

Collective excitations of 3He B in the presence of superflow

The energy levels of collective excitations of 3He B are given in the presence of superflow. There is level splitting due to the distortion of the energy gap which should be observable experimentally.

Depairing critical current of 3He-B at all temperatures including gap distortion

Gap functions and superfluid densities are calculated at all temperatures in the presence of superflow. The critical current undergoes a significant reduction due to gap distortion.

Anisotropic gap distortion due to superflow and the depairing critical current in superfluid 3He-B

We have calculated the pair-breaking critical current for superfluid 3He-B at all temperatures by taking into account the anisotropic distortion of the order parameter in the presence of superflow. We find that the component of the order parameter along the flow δ∥ is strongly reduced, while δ⊥, the component perpendicular to the flow, slightly increases. The superfluid density ϱs has also been determined as a function of the superfluid velocity v s. Fermi liquid corrections are explicitly included and it is shown that these corrections lead to a drastic change in the functional dependence of δ∥, δ⊥, ϱs, etc., on v s. In contrast to this, the pair-breaking critical current is shown to be independent of the Fermi liquid corrections.

Textures in narrow cylinders in superfluid 3He-A

We calculate the equilibrium configurations of three textures in a narrow cylinder in the presence of superflow along the cylinder axis. The Mermin-Ho texture is shown to be unstable against a small twist in the dipole-free limit even in the absence of superflow. The radial disgyration undergoes a second-order transition forqR ∼-3.31, while the circular disgyration gives rise to a helical texture forpR ≳ 3.5, whereR is the radius of the cylinder andq [≡ (2m/ħ)V s]andp are momenta associated with superflow. The associated nuclear magnetic resonance frequencies are determined.

Flow-induced soliton lattice in superfluid 3He-A

Abstract It is shown that in the presence of superflow, υ s , parallel to a strong magnetic field H (| H | ≫ 20 Oe), the uniform texture becomes unstable againts the formation of a one dimensional soliton lattice forυ s ⩾ υ c2 (≈1 mm/s). The period of the resulting soliton lattice as well as the related NMR frequencies are determined as functions of υ s .

Field-induced surface texture in 3He-A in the presence of superflow

The effect of superflow on the magnetic field-induced surface texture in /sup 3/He-A is studied theoretically. We find that in the presence of small superflow the surface texture becomes nonplanar. The NMR satellite frequencies associated with the surface texture are obtained.

Stability of helical textures in 3HeA in the presence of superflow

We analyze the stability of a variety of uniform textures in superfluid 3HeA in the presence of superflow p. We find below Tins a class of stable helical l̂ textures, where l̂ is no longer aligned with p but winds around it with a constant pitch .

Helical textures in 3He-A in the presence of superflow and magnetic field

Helical textures in 3He-A in the presence of superflow and magnetic field

Simple theoretical models of the behaviour of shear waves in the interaction of superflow with the vortex lattice

An explanation of the behaviour of the vortex lattice in the presence of superflow is proposed, introducing an helicoidal deformation of the vortices and a new characteristic distance: the wavelength of the shear waves associated with the frequency of rotation.