Questions tagged [superfluidity]

A flow with no viscosity

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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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819 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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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 ...
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What's the role of BEC in superfluidity?

I'm writing about superfluid $^4$He. I've seen in some places that the transition to superfluid is attributed to Bose-Einstein condensation, but then in others that this model needs a massive amount ...
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1answer
70 views

Can superfluids communicate faster than light?

According to this video: https://www.youtube.com/watch?v=ueVTzEB3tJ8 A superfluid "flows without friction" and "all of the atoms in a superfluid are in the same quantum state." What strikes me as odd ...
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1answer
267 views

Symmetry breaking and Superfluid - Mott Insulator transition

I know my question is similar to what mentioned in this post: Symmetry breaking in Bose-Hubbard model. Yet, I don't find it clear. I've in mind a 1D Bose-Hubbard Hamiltonian. Moving from the Mott ...
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1answer
342 views

What causes Superfluidity?

Superfluidity is the frictionless flow and other exotic behavior observed in liquid helium at temperatures near absolute zero. The unusual behavior arises from quantum mechanical effects. What are ...
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78 views

Do superfluids lack inertia and/or don't exist with a finite speed of sound?

I've been reading a few things on other sources about superfluids and what kind of propulsion would work in them. Supposedly a propeller won't work in a superfluid, but I'm having a hard time ...
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Does every superfluid have a normal and a superfluid component?

After seeing the question Will a propeller work in a superfluid?, I remembered an old video by Alfred Leitner (1'50'' and 3'00'')where he experimentally shows that liquid Helium below the $\lambda$ ...
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Will a propeller work in a superfluid?

Will a propeller work in a superfluid? Opinions differ.
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Why superfluid is described by interacting with goldstone boson?

I've read chapter about superfluids of Anthony Zee's QFT in nutshell and it is still not clear, why the energy spectrum of massless field only is taken into account to describe superfluid? In that ...
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Calculating first harmonic of second sound

I can't find some of the values I need for this calculation, which I'm trying to do prior to an experiment around superfluidity. Specifically I am trying to get a rough estimate of the first harmonic ...
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1answer
202 views

Why are superfluids thermodynamically possible?

I was reading about superfluids and how they can flow without loss of any kinetic energy over time, specifically they can form vortices that rotate indefinitely. However I do not understand why this ...
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109 views

What are the limitations of Gross-Pitaevskij equation?

I'm a mathematician and I'm studying as an aside something about superfluids. If I understood correctly in some kind of superfluids as Bose-Einstein Condensate a wave in the fluid must satisfy the ...
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2answers
266 views

Fermi Point - What is it?

I'm trying to learn more about the idea of the quantum vacuum being a superfluid and how that can unify physics, but after all the reading I've done I can't quite nail down a conceptual understanding ...
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Univerality Class and Momentum Space Topology

I'm very interested in learning about Superfluid Vacuum Theory, and one thing I have come across is the statement that the universality classes are protected by momentum space topology. So I was ...
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A Strange Plastic (as opposed to Elastic) Balloon?

Today, while contemplating on the absurdity of life (or, in other words, procrastinating as usual), I stumbled across a strange inflated balloon, the first of its kind that I have ever seen as per my ...
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1answer
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Time of flight images of Bose-Hubbard model

on the website of Immanuel Bloch, you can find time of flight images of bosonic particles inside an optical lattice for different values of the depth of the lattice. (http://www.quantum.physik.uni-...
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How can helium be liquid at absolute zero, given the Third Law of Thermodynamics? [duplicate]

I learned recently that Helium is a liquid even at 0K. Doesn't that mean that it still have some entropy? If so, does it not violate the postulate of thermodynamics that states that entropy must go to ...
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222 views

order of BKT phase transition

What is the order of the BKT phase transition (first or second), that is the phase transition in 2d in which thermal vortices destroy any order in the system. How is this connected to the "universal ...
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1answer
144 views

Rigidity and superflow

In the book "Introduction to Many-Body Physics" by Piers Coleman, it is argued (page 406) that a momentum supercurrent (superflow) corresponds to sheer stress in a crystal. What would be a simple ...
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1answer
124 views

How is angular momentum stored in the superfluid component of pulsars?

I am trying to understand current theories about why pulsars glitch. I have come across two explanations that I'm assuming are complementary, but which I am having trouble reconciling. The inner ...
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1answer
757 views

Can superfluids pass through ordinary baryonic matter?

Since superfluids consists of integer spin bosons or effective bosonic Cooper-paired fermions, Pauli Exclusion Principle does not apply to them. They can thus occupy the same quantum state as any ...
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Capturing superfluid condensation with exact diagonalization

Doing exact diagonalization on bosonic systems is tricky, because the possibility of multiple occupancy means that even the single-site Hilbert space is infinite-dimensional. It's my understanding ...
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Solution to periodic potential GP equation

Consider the boundary condition $\psi(0)=\psi(2\pi)$ and the Hamiltonian (and corresponding nonlinear Schrödinger equation): $$\left[\left(-i\frac{\partial}{\partial\theta}-\Omega\right)^2+2\pi\gamma|\...
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1answer
251 views

Rotation of superfluid

I have two questions related to rotation of superfluids. Firstly, what is the main reason that superfluid cannot rotate as a whole object ? (I found that it is true in Landau's Statistical Physics but ...
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1answer
568 views

What is the Single Mode Approximation?

When Girvin and co-workers solved the excited collective modes called magneto-rotons in Fractional Quantum Hall liquids, they used something called the Single Mode Approximation (SMA). My question is: ...
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Where should I start learning Landau's theory of superfluidity?

Where should I start learning Landau's theory of superfluidity? For a second year undergraduate.
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Bulk modulus of supercrtical air

For gaseous state air has bulk modulus of ~pressure, but what about bulk modulus values about the supercritical pressure treshold, are these still pretty much same as the pressure or does this ...
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1answer
108 views

Why is the symmetric phase in a Bose gas not superfluid?

In the theory of superfluidity in weakly interacting Bose gases, one finds that in the symmetric phase the exctitations have the dispersion relation $\omega = \frac{k^2}{2m}-\mu$ with gap $\Delta=-\...
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1answer
225 views

Adiabatic transition from superfluid to Mott insulator?

I have a question about the dynamical passage from superfluid to Mott insulator state in the Bose-Hubbard model. Is it possible to go from superfluid region to the Mott insulator by changing the ...
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1answer
1k views

What is the difference between superfluidity and Bose condensation?

My question is about zero-temperature ground state of a Bose system. Suppose that the system stabilizes a BEC order parameter, say $\langle b^+ \rangle$, and fixes its phase. Is this a superfluid? And ...
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187 views

Do superfluids have zero viscosity?

The Wikipedia definition of a super fluid is: Superfluidity is a state of matter in which the matter behaves like a fluid with zero viscosity As a fluid dynamics guy, I have a hard time imagining ...
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Why is chemical potential, μ=0 when calculating critical temperature of BECs?

How do we justify taking the chemical potential, $\mu$ as $0$ when calculating the critical temperature of Bose-Einstein Condensates (BECs)? I apologise as I do not how to use LaTeX, for if I did the ...
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1answer
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Why the total nuclear spin is only 0 or 2 for singlet s-wave scatting with $M_F=0$?

when I read the lecture of Feshbach resonance, the lecture on page 15 said that it want to find all s-wave molecules for $M_F=0$. It said when the two atoms are singlet, the total nuclear spin is only ...
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Notation in a neutron star superfluidity

In this article "Neutron Star and Superfluidity", by Ka Wai Lou: http://guava.physics.uiuc.edu/~nigel/courses/569/Essays_Fall2010/Files/lo.pdf symbols as $^1S_0$ and $^3 P_2$ are shown, but I not sure ...
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How does superfluid helium interact with ultrasound?

Containing liquid helium in it's superfluid state is of course known to be problematic. Escape by crawling up container walls to 'leak' through solid containers and similar difficulties being a ...
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221 views

Are there any practical applications of Mott insulators and Superfluids?

The potential applications of Bose-Einstein condensated is discussed here, I was wondering whether anyone could produce a similar argument for Superfluids and Mott insulators. EDIT: I fully realise ...
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Can we 'dope' a fluid to make it become a superfluid?

The only element that can become a superfluid is Helium (He-3 and He-4) since it does not solidify not matter how cold it gets, hence it can reach the superfluid transition temperature whilst still a ...
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What is the equation for the elementary-excitation spectrum of superfluid heluim over whole momentum space?

I have a simple question. What is the equation for the elementary-excitation spectrum of superfluid helium over whole momentum space, not just near the origin (i.e., phonon excitations $\epsilon=cp$) ...
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Superconductivity and superfluidity energy dissipation

All articles say that in superconductive state, the materials have exactly zero resistance, but is this the case in real life experiment?, because if this were true, a process without energy ...
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245 views

Do neutron stars emit stellar flares?

Since stellar flares are formed from the magnetic energy of a star, is it probable to assume that neutron stars can emit stellar flares as well? If so, how would the super fluid material of the star ...
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Why are quantum vortices so large?

Quantum vortices in helium are almost macroscopic, and can be be imaged in a light microscope: http://www.aps.org/units/dfd/pressroom/papers/gaff09.cfm How can vorticity be quantized on such a large ...
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1answer
53 views

How long to drain superfluid from a container with a small hole in the bottom?

The most naive way of thinking would suggest that because there is no viscosity it drains as fast as if you turned the container upside down and let it fall out. However, assuming the hole is smaller ...
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1answer
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How to choose which atoms to cool using optical cooling technology?

Which atoms are easiest to cool down to very low temperatures (e.g. mK)? Which quantities does one need to look at? My very naive guesses so far are: Their mass: the heavier they are they least ...
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203 views

$U(1)$ gauge symmetry in superfluid

The conventional superfluid phase in a Bose-Hubbard ground state has $U(1)$ symmetry. In the presence of spin-orbit coupling (SOC), the superfluid ground state has non-uniform phases. Why do people in ...
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2answers
221 views

Viscosity, bubbles and (super)fluids

3-part question, but I think it's simple enough... Does the tendency for cavitation in a fluid depend on its viscosity? If so what does this imply for superfluids, having 0 viscosity? And for that ...
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221 views

Why does not the bare interaction potential appear in the Bogoliubov theory?

They use some effective potential defined by the s-wave scattering length, but not the bare atom-atom interaction $V(r)$. Why? It is standard practice in second quantization to use the bare ...
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Statistical field theories on topological defects

Systems like superconductors and superfluids are often treated by specifying some phenomenological mean field theory where the free energy is given as a functional of some order parameter field. Given ...
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physics of the beaker experiment for superfluid helium

here is an illustration and explanation of the beaker experiment over superfluid helium: So, according to this experiment, can anyone say what is the cause? I mean the superfluids are disconnected ...