Questions tagged [superfluidity]
A flow with no viscosity
193
questions
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22 views
What happens when you stir a superfluid?
If I stir up some liquid helium in a container with an irregular shape, I'd expect to see a vortex break up into smaller and smaller vortices. Since liquid helium has no viscosity, I would also expect ...
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0answers
15 views
Does the isothermal compressibility diverge at the lambda line in Helium-4?
Helium-4 has a normal-superfluid phase transition which corresponds to the lambda line in the P-T diagram. The heat capacity at constant pressure $C_p$ shows a discontinuity when the lambda line is ...
2
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1answer
31 views
Closed form solution of the normal density of a superfluid for the Bogoliubov spectrum
I've been trying to solve the following definite integral
$$
\int_0^\infty dx\, x^4\, \frac{e^{\sqrt{x^4+2 x^2}/Tp}}{\left(e^{\sqrt{x^4+2 x^2}/Tp}-1\right)^2}\, ,\quad Tp = \frac{T}{Un}
$$
This is the ...
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0answers
67 views
Closed form solution to normal fluid density integral in the two fluid model [migrated]
I've been trying to solve the following definite integral
$$
\int_0^\infty dx\, x^4\, \frac{e^{x^2+a}}{\left(e^{x^2+a}-1\right)^2}\quad , \qquad a>0\, .
$$
This is the density of the normal part of ...
3
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1answer
58 views
Superfluids in areogel and porous media: why?
Aerogels are materials that are like ~90% or more air. As I understand, the topology of the material (i.e. of that part of the aerogel that is not air) is not such that air is contained into bubbles. ...
1
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1answer
50 views
Two different to do Bogobliubov transformation but sees to be contradictary
When try to do bogoliubov transformation on a weak-interaction cold atoms with uniform velocity $\vec{v}$, I used two different approaches, giving two different results.
The Hamiltonian is
$$\hat{H}=\...
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0answers
21 views
What happens to a superfluid after it falls out of a tap?
Imagine a container filled with a super-fluid, which has zero viscosity (or, equivalently, the value of the Reynold number is infinite for the superfluid). There is a valve connected to the container ...
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0answers
43 views
Why do molecules in superfluid move together?
From this question and corresponding answers, I gather that Bose-Einstein condensate makes the gas going to ground state and the ground state is the momentum zero state.
But superfluidity is not about ...
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0answers
22 views
Is there a relation between charged energy gap and neutral energy gap?
While I am studying different quantum phases in many-body systems, I found superfluid is called a gapless phase $(\Delta_0=0)$ while Mott insulator being a gapped phase $(\Delta_0 \neq 0)$. In this ...
1
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1answer
65 views
How to observe off-diagonal long range order in superfluid?
off-diagonal long range order in superfluid is an effect that the matrix element of the single particle's density matrix remains finite in the long distance limit.
My question is: how to prove this ...
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1answer
39 views
Dispersion Relation of Quasiparticle in Superfluid
I am now reading a book "Superconductivity, Superfluids, and Condensates" by Jame F. Annett. I am stuck at the part of writing dispersion relation of the quasiparticle in superfluid here. ...
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0answers
18 views
Under what conditions would neutrons pair up to produce bosons in the core of neutron star to form Bose-Einstein Condensates?
In Neutron star, the fermions get converted to bosons and form Bose-Einstein Condensates in its core. I couldn't find under what specific condition this phenomena takes place.
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18 views
Are there any models for fluxon transport in type-II superconductors?
I am trying to understand the motion/transport of fluxons or vortices under an applied current density $\vec{J}$ in a type-II superconductor subjected to a spatially varying magnetic field. I ...
4
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2answers
189 views
Is the zero-point energy of helium stronger than other liquids to disfavour freezing?
Under normal atmospheric pressures, liquid helium does not freeze even when cooled very close to absolute zero. This is attributed to the uncertainty principle or due to zero-point energy.
But the ...
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0answers
13 views
Theoretical construction of the He-3 phase diagram from Landau-Fermi liquid theory
The phase diagram of He-3 is well known at this point, with a clear superfluid phase, gas phase, and "normal" Fermi liquid phase (see below from Wikipedia):
However, the majority of the discussion on ...
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23 views
A detail in Bougliobov theory of superfluidity
I'm currently studying superfluidity following Mahan's book and there's a detail I'm not understanding.
The exchange energy of the fluid (boson gas) in the normal state is written as
$\begin{aligned}...
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0answers
30 views
Would a solid object submerged in a super fluid conserve its momemtum as it travels?
Reading about Helium at low temperatures has me scratching my head in confusion. Liquid Helium-4 at around 2K exhibits properties of a super fluid. Viscosity of a super fluid is equal to zero, which ...
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0answers
28 views
Diagrammatic calcilation of superfluid and normal densities
Superfluid $\rho_\mathrm{s}$ and normal $\rho_\mathrm{n}$ densities in a Bose-condensed system can be calculated microscopically from the current-current response function $\chi_{\alpha\beta}(\mathbf{...
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2answers
89 views
How does the energy gap explain the non-dissipative nature of a superconductor? [duplicate]
The energy spectrum of a BCS superconductor contains an energy gap. How does the existence of this energy gap explain that there is no dissipation of energy in a superconductor? There are also energy ...
1
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1answer
23 views
Two equivalent supercurrent expressions from Ginzburg-Landau theory?
This is a seemingly odd question, but it's come up in a few different areas related to the supercurrent from GL theory. I am happy that one can vary wrt to the vector potential to option the equation ...
2
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1answer
52 views
Chemical potential in superfluids and superconductors
It's been known for a long time, probably since the formulation of Landau's two-fluid model of superfluid 4He, that superfluids accelerate in response to gradients in the chemical potential (per unit ...
1
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1answer
88 views
Critical point for superfluid
Critical point for liquid-gas transition:
Where critical point for He3?
For He4?
Ising model lie in $Ising_3$ universality class. In which universality classes lie critical points of helium?
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1answer
49 views
Are the definition of superfluid order parameter in real space and $k$-space same?
Considering fermions tight bind model,in real space the superfluid order parameter can be writed as $$\Delta=g\langle c_{i \uparrow}c_{i\downarrow}\rangle$$ In k space, the definetion of ...
2
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1answer
81 views
Gross-Pitaevskii equation and healing length
I am given the following GPE:
$$-\frac{\hbar^2}{2mr}\frac{d}{dr} \Big( r \frac{d\chi}{dr} \Big) + \frac{\hbar^2}{2mr^2} \chi + (U_0 \chi^2-\mu)\chi=0.$$
I am asked to derive the healing length (not ...
0
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1answer
74 views
Energy of vortex-antivortex pair
I am given the following field in 2d:
$$\theta(\mathbf{x}) = \phi(\mathbf{x}-\mathbf{x}_1) - \phi(\mathbf{x}-\mathbf{x}_2),$$
where $\mathbf{x}_1,\mathbf{x}_2$ are the position of the vortex and ...
2
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0answers
48 views
What is the form of the dynamical term in Ginzburg-Landau theory for superfluids and superconductors
Starting with a classical Ginzburg-Landau theory of a superconductor,
$\mathcal{L} = a |\nabla\psi|^2 + b |\psi|^2 + c |\psi|^4 +...$.
suppose I want to include quantum (i.e temporal) fluctuations. ...
2
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0answers
28 views
Thermalization of BEC dark matter
In the context of BEC/superfluid dark matter, one of the important requirements is that - within galaxies - dark matter thermalizes [1]. Axions are appropriate in this regieme, as their self-...
1
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1answer
51 views
Number density of phonons in superfluid
I'm reading Superfluidity and Superconductivity by Tilley & Tilley. In section 2.4, the argument is made that the normal component of superfluid helium consists of phonons and rotons. The ...
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0answers
42 views
Why does going close to absolute zero take out friction? [duplicate]
I read in a physics book that when you get close to absolute zero, a liquid stops having friction. Why is that (if itās even true, that is)?
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0answers
31 views
Second sound in superfluids and solids
I am trying to get a handle on the phenomenon of second sound. It most famously occurs in superfluids at finite temperature. Here, according to Landau, superfluid phonons (which exist at zero ...
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2answers
88 views
Can surface tension be zero? [duplicate]
Inshort Surface tension occurs due to imbalance of the intermolecular forces of attraction on water molecules. At the surface it is more so net force is inwards.
I read somewhere on this app that "...
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0answers
20 views
What do you mean by quark gluon plasma is frictionless?
I read about the similarities between quark gluon plasma and Bose Einstein condensate especially both are frictionless, I know generally when everday object rubs against one another the electrons get ...
0
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1answer
33 views
Can the Superfluid Rollin effect cause a closed-loop motion effect?
Superfluids such as liquid helium cooled below the lambda point exhibit the Rollin effect where a thin film climbs the walls of the vessel. This still and video from the 1950s shows the effect, where ...
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0answers
25 views
Two-fluid model of helium II and beaker experiment, superleaks etc
It is an assumption of the two-fluid model that the normal and superfluid components of helium II cannot be physically separated, but surely the beaker experiment, in which only the superfluid ...
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0answers
25 views
Conservation of momentum in superfluids
Superfluids such as $^4\text{He}$ under Lambda temperature displays properties of superfluids, having nearly $0$ viscosity. This allows the fluid to pass through space packed with fine powders that ...
2
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1answer
87 views
What exactly is color superconductivity?
I'm having a hard time visualizing exactly what would happen. What similarities does it share with our usual superconductivity and what would be different?
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2answers
89 views
How and why Liquid helium climbs the walls of the container it is kept in?
Liquid helium (He-II) shows a strange phenomenon, where it flows on its own, forming films across the surfaces of the container it is kept in. How and why this happens and how is it possible?
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0answers
23 views
Is the Andreev-Bashkin effect a beyond-mean-field effect?
I am reading about the Andreev-Bashkin effect, which concerns the current drag from the interaction between two superfluids. Basically, the interaction between two coupled superfluids leads to the ...
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0answers
26 views
Superfluid Vortex Lines Bifurcation and Winding Numbers
Vortex lines in superfluids are characterized by their quantised circulation: $k = \frac{h}{m}\times n$, where $n$ is the winding number in the sense of a topological winding number. Now, most vortex ...
0
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1answer
32 views
What happens, if a liquid/gas is kept on constant high pressure in a closed container for a long period?
On applying non-increasing constant pressure,
I need to understand the case for liquid and gas.
If container is not inescapable:
Will the liquid/gas heat up?
Will any of their properties change?
...
0
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2answers
248 views
Why don't we use liquid helium superfluids for infinite clean energy?
Liquid helium, at a low enough temperature, becomes a superfluid. This would mean that if we stirred it, it would keep spinning forever. Surely this means we could use a small amount of liquid helium ...
13
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2answers
491 views
Are there Goldstone bosons in 1D or 2D?
The Mermin-Wagner theorem states that
continuous symmetries cannot be spontaneously broken at finite temperature in systems with short-range interactions in dimensions d ā¤ 2.
And Goldstone bosons ...
5
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1answer
179 views
Charge-Vortex Duality for Bosons
Consider a (2+1)d continuum field theory with the Minkowski action
$$\mathcal{L}=|\partial\phi|^2-r|\phi|^2-u|\phi|^4,$$
where $\phi$ is a complex field. The theory undergoes a quantum phase ...
1
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0answers
22 views
Convert Normal water to cool instantly [closed]
Is it possible to convert the hot/normal water to cold steam instantly(may be within 1/2hr) without using refrigerators etc. If yes, how far can the cold steam travel. I am not sure with all the fluid ...
3
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2answers
341 views
What's the difference and relationship between perfect fluid and superfluid?
Sorry for this naive question, I just cannot find good references talking about the difference and relationship between perfect fluid and superfluid. Could someone explain this to me or point me to ...
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0answers
11 views
Is the streaming of a superliquid through a circular tube equivalent to the current running in a circular piece of superconducting material?
When a superfluid streams endlessly through an isolated circular tube is the same mechanism at work as in the endless current moving through an isolated circular piece of superconducting material? Is ...
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0answers
20 views
How will a rotating, circular, and cylindrical body of a superfluid develop in outer space?
Let's consider a rotating (about its center, in the plane cutting the initial circular and cylindrical form into two halves), circular, and cylindrical body of a superfluid somewhere in outer space. ...
2
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0answers
50 views
Do Goldstone modes with linear dispersion always correspond to superfluidity?
For a superfluid, we get that the Goldstone modes has a linear dispersion. $\omega=vk$ where $v$ will be a critical velocity. We can have no excitations caused by impurities with a velocity less that ...
0
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1answer
80 views
Why we can't write low energy effective field theory for a gapless system?
Assume that we have an Hamiltonian $$H=H_0+H_{int}$$
where $H_0$ has gappless excitations and $H_{int}$ has usual two body interactions.
If $H_0$ were gapped I would able to get low energy effective ...
2
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0answers
76 views
Energy dissipation from a black hole by neutrinos
Could the high gravitation field of a black hole cause neutrinos to form a Fermi gas or superfluid? Could these neutrinos from the neutrino background of the big bang whose temperature and deBroglie ...
