# Questions tagged [superfluidity]

A flow with no viscosity

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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 ...
2answers
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### 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 ...
1answer
43 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 ...
2answers
94 views

### 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 ...
1answer
334 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 $h_{c2}$, ...
1answer
893 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 ...
1answer
91 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 ...
0answers
111 views

### 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 ...
1answer
71 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 ...
1answer
276 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 ...
1answer
411 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 ...
1answer
80 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 ...
1answer
308 views

### 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 $\lambda$ ...
3answers
4k views

### Will a propeller work in a superfluid?

Will a propeller work in a superfluid? Opinions differ.
1answer
191 views

### 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 ...
0answers
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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 ...
1answer
212 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 ...
1answer
110 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 ...
2answers
276 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 ...
1answer
34 views

### 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 ...
3answers
226 views

### 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 ...
1answer
83 views

### 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-...
1answer
2k views

### 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 ...
0answers
229 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 ...
1answer
147 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 ...
1answer
125 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 ...
1answer
775 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 ...
0answers
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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 ...
0answers
29 views

### 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|\...
1answer
262 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 ...
1answer
593 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 ...
1answer
109 views