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Questions tagged [superfluidity]

A flow with no viscosity

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What if an ocean planet is covered by superfluid ocean? [closed]

It is possible that an ocean planet can be covered by superfluid state liquid. What will happens on this kind of planet? Will there be any changes to tide? Will there be strong magnetic field? Will ...
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1answer
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BCS theory for neutral fermions

As I understand it, Cooper pairs form between two fermions and are the cause of superconductivity. I was told by a teacher that the formation of Cooper pairs and BCS theory requires both fermions to ...
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What would happen if we test the Hagen-Poiseuille law with a superfluid?

When we have a laminar flow we can test the Hagen-Poiseuille law from the pressure difference created by the flow of the fluid. This process is created due to conservation of total energy but the ...
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1answer
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Does (Tomas) Bohr's modified double slit argument really doom Couder's quantum/classical fluid dynamics analogy?

I'm just an amateur, probably why I find the de Broglie/Bohm/Couder approach to QM compelling. But Copenhagen struck back: in a coincidence, Bohr's grandson is a fluid physicist who claims that ...
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1answer
20 views

How do we imagine the transition between phonons and rotons?

In the theory of superfluidity, we have both phonon and roton excitations. Phonons are long-range density fluctuations (sound waves) and rotons are short-range (atomic scale) circulations of the atoms ...
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What macroscopic fields exist around color supercurrent?

For an ordinary superconductor such as Lead, charge supercurrent gives rise to a magnetic field around the whole material for low enough currents. At large enough currents, the superconductor will ...
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1answer
30 views

What is *diagonal* long range order?

I have seen this question about off-diagonal long range order in superfluids. What’s the difference and the significance between long range diagonal and off-diagonal long range order?
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What is the link between superfluids and BEC?

i’m studying superfluids (in particular $^4 He$) and one of the first theorical apporoach was with Bose-Einstein condensation and i know that we can calculate the $T_c$ and it is close to the the ...
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1answer
96 views

Vortex in superfluid?

I'm studying superfluid helium 4. I have studied that the superfluid has a velocity : $ \vec{v}_s = \frac{\hbar}{m} \vec{\nabla} \varphi(\vec{r}) $ $\rightarrow$ $ \nabla \times \vec{v}_s = 0 $. (...
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vortex anti-vortex configuration to ground state [closed]

i'm studying kosterlitz transition. I'm reading this: https://assets.nobelprize.org/uploads/2018/06/advanced-physicsprize2016-1.pdf?_ga=2.51324009.1302372948.1538119052-1605759177.1538119052 Now ...
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1answer
223 views

Is dark matter a superfluid?

The fact that the dark matter halos surrounding colliding galactic clusters simply pass through each other without interacting has a simple explanation. If they are superfluid bodies, wouldn't be ...
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17 views

Why the form factors on the green function of relativistic two-component liquid model for superfluid have this form?

I am working in trying to understand Appendix A of arXiv:0906.4810. On this appendix, the authors set up an external velocity field perturbating a superfluid, described by a two-component model. This ...
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1answer
73 views

Holographic Superfluid Space Time and Temperature

I am approaching this from a layman’s perspective and curious about what those more expert in the field have to say about my understanding of Superfluid vacuum theory and the holographic principle and ...
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1answer
56 views

A conservation law in fluid dynamics

Let's consider a water flow in two dimensional space, assume the velocity field is $\vec{v}(t,x,y)$, we can define: $$\rho=\hat{z}\cdot(\partial_x\vec{v}\times \partial_y\vec{v})$$ $$j^x=\hat{z}\cdot(...
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flowing water with really high Reynolds number hitting a wall not prependicular

A streamline of water is incident upon a wall at an angle $\theta$ where $\theta \neq 90°$ Friction can be neglected. What will the force exerted on the point of incidence be? If we assume the flow ...
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29 views

Topological properties of dark solitons in superfluid systems

In the study of superfluid systems, vortices are often referred to as "topological excitations", because the winding of the phase of the superfluid order parameter around a vortex is a topological ...
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1answer
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Resource request: Superfluid helium

I am wondering if anybody could recommend any good textbooks on the subject. So far, I have discovered (but not yet had a chance to read), a chapter in Landau-Lifshitz fluid mechanics (love Landau-...
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1answer
50 views

Superfluidity: separation of quantised vortices in a vortex tangle

It is often quoted (see https://doi.org/10.1016/j.piutam.2013.09.008) that the separation $\delta$ between quantised vortices in a vortex tangle in a superfluid is approximately $$\delta \approx L^{-...
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The correct expression for pressure, temperature in Landau's 2-fluid model

Setup: the system of equations I would like to numerically solve the equations of motion in Landau's [Ref (1)] two-fluid description of superfluid He II, which are $$ \frac{\partial \rho}{\partial t}...
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1answer
102 views

Is the superfluid state a coherent state?

In the normal to a superfluid phase transition, U(1) symmetry related to particle number conservation is spontaneously broken which seems to imply that the superfluid state is a state in which there ...
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141 views

Whats the speed of sound in the superfluid vacuum?

In the superfluid vacuum theory, sound can propagate in the vacuum, as it is connected to vacuum energy considerations. Quote: "There are several theories of a superfluid vacuum. These theories have ...
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31 views

Superfluids: what is the physics that predicts how thick is a Rollin film?

I do not have much familiarity with the physics of fluids (or superfluids, by the way) and I couldn't find what physically makes a Rollin film to be as thin as it is (I know that the order of ...
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1answer
47 views

Is the $\lambda$ point in superfluid helium understood?

When liquid helium is cooled below a certain temperature, it undergoes a second phase transition from He I to He II. The specific heat spikes at the famous lambda point. Is this spike in the specific ...
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Does Helium really stay a liquid at $0K$ due to zero-point motion?

People often say that helium stays a liquid at low temperatures due to "zero point motion.'' I decided to test this for myself. Based on this source which estimates that the depth of the potential ...
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50 views

Superfluidity in one dimension?

Why is there no superfluidity in one dimension? What is the connection to higher dimensional superfluidity, static/thermodynamical, and dynamical responses?
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1answer
58 views

Why do rotons correspond to the minimum of the dispersion curve?

The dispersion curve for superfluid helium-4 is given above. To my knowledge, the first paper that was able to argue that the curve should take this shape from first principles was Feynman's 1954 ...
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Definition of Superfluid with no Bose-Einstein condensation?

A BEC with no superfluidity is referred to as Bose Glass (due to S. Yukalov to my knowledge). Is anyone aware of a similar definition for systems which exhibit superfluid behaviour but are not Bose-...
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Observational evidence for superfluidity in neutron stars

What is the earliest evidence for the existence of superfluidity in neutron stars? I'm about to present the subject in a seminar and I'm under the impression that at the moment there is no ...
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1answer
98 views

Quasiclassical propagator

Sometimes they are referred as Keldysh quasiclassical propagator or Eilenberger propagator. How the quasiclassical propagator is derived? How they are implement with a simple case of a Green's ...
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1answer
191 views

Landau critical velocity and sound velocity

The definition of Landau critical velocity is $v_L=\min_{q}\{\frac{\omega(q)}{q}\}$, where $\omega(q)$ is the spectrum of excitations. The viscosity vanishes when the object is moving through the ...
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125 views

Superfluidity book recommendation

I'm preparing for a senior undergrad seminar on superfluidity and quantized vortices, and my professor seems to prefer old textbooks, so I wondered what modern (~90's onwards) books on these phenomena ...
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1answer
39 views

Energy of the excitation in the superfluid

According to the chapter 1.3: Superfluidity, from the book "Methods of Quantum Field Theory In Statistical Physics by A.A Abrikosov, it is written that Consider a Bose liquid at absolute zero, ...
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Is gapless spectrum necessary for superfluity

In 3D interacting Boson system, the condensate leads to a gapless spectrum and superfluidity. The same gapless spectrum for 2D with quasi-condensate (correct me if it is wrong ). I am wondering if it ...
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1answer
172 views

Partition function of weakly interacting Bose gas

In the Bogoliuobov theory of superfluidity, the hamiltonian of a system of weakly interacting bosons in second quantized notation is diagonalized with the following result: $$\hat H = H_0 \hat1 + \...
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169 views

Is density fluctuation gapless in superfluid?

Deep in the superfluid phase, the superfluid order parameter $\phi$ can be decomposed into the amplitude (density) mode $\rho$ and the phase mode $\theta$ as $$\phi=\sqrt{\rho} e^{\mathrm{i}\theta}.$$ ...
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Introductory condensed matter physics book [duplicate]

I need a book for general condensed matter physics, preferably at an undergraduate level, e.g. at Ashcroft and Mermin's level or below. Modern applications are preferred.
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101 views

Superconductivity and superfluidity in bosonic and fermionic condensates

Can bosonic and fermionic condensates explain superfluid and superconducting properties? Are they better than the theory of BCS and Landau? Edited: My question is based in this lecture pesentation ...
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Effect of electromagnetic field on atoms of supercooled helium in a vacuum

I'm trying to predict what would happen to supercooled helium atoms in a vacuum when a strong electromagnetic field was present nearby. I think that a Lorentz force would move the helium atoms away ...
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2answers
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Is there a phase coexistence line below the critical temperature $T_c$ in normal to superfluid transition?

In the case of water, there is a phase coexistence line (called the liquid-gas coexistence curve) which ends in a critical point. And this line separates the gas phase from the liquid phase in the P-T ...
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Why do pairing and condensation occur simultaneously in superconductors?

Bose condensation in the weak-coupling limit (such as BCS superconductors) and the strong-coupling limit (like BECs of atoms) can be unified into a single framework by the BEC-BCS crossover. One key ...
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1answer
165 views

Are there Goldstone bosons in the spontaneous normal to superfluid transition?

The normal to the superfluid transition of liquid helium breaks is a U(1) global symmetry. Since it is a continuous, global symmetry (unlike superconductivity which is a gauge theory), I expect that ...
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The appearance of a gapless phase mode in Landau Ginzburg theory of charged superconductor

My question is simply: Why do the Landau Ginzburg(LG) theory of superconductors describe a phase mode which is ungapped/massless when it should be promoted to the plasma frequency? I will try to ...
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57 views

The single valuedness of the superfluid and superconductor order parameter

For a superfluid, why does the phase of the order-parameter must be single valued? Does the answer differ for a superconductor? Does the answer depends on the topology of the manifold?
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Sod shock tube - Contact Discontinuity

sorry for bothering with my question. https://en.wikipedia.org/wiki/Sod_shock_tube I have trying to understand, how is it possible to have a discontinuity on Density and not on Pressure. I don't ...
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2answers
58 views

Quantification of the circulation in superfluids : why does the phase jump by $2 \pi$?

In superfluidity we have the current density that is $j=\frac{h}{m} \vec{\nabla}(\phi)$ Where the wavefunction describing the system is : $\psi(\vec r)=\sqrt{n_s}e^{i \phi(\vec{r})}$ We then ...
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1answer
42 views

How superfluidity can arise at extremely high temperatures

I'm a mathematicians and I don't have a big knowledge of physics. I've heard that superfluidity can arise inside a neutron star and I've given to understand that this has to do with a hugh density ...
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2answers
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The two-current model of superconductivity

Standard text books (Landau and Lifshitz etc) explain that the correct macroscopic theory of a superfluid is two-fluid hydrodynamics. A superfluid is made of two components, a viscous normal fluid and ...
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1answer
267 views

Why are superfluid vortex lattices stable?

Both (a) neutral superfluids that are externally rotated, and (b) type-II superconductors (i.e. charged superfluids) under applied magnetic fields between the critical fields $h_{c1}$ and $h_{c2}$, ...
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1answer
589 views

What causes liquid helium to climb walls?

It is a phenomenon which can be observed if your search on the web. Apparently liquid Helium can crawl up through walls. Does every superfluid do this crawling action or is it just special for liquid ...
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1answer
73 views

Why do superfluid vortices form a lattice?

I often hear that in a superfluid, vortices get arranged in a lattice but I don't understand why and I've been hard pressed to find a discussion of it online. I'm aware that vortices should repel ...