Questions tagged [superfluidity]

A flow with no viscosity

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105 views

Testing the speed of gravitational waves in superfluids

Ok. Light can be slowed down in superfluids. I would like to know whether if a Cavendish like experiment could be possible within inside superfluids i.e, to rotate two balls such that to observe their ...
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Feshbach resonance in simple terms

I was reading up Feshbach resonances in cold atoms and I was unable to grasp the concept. I will tell you what I have understood. We consider two body scattering processes elastic as well as inelastic....
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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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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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228 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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Two-fluid description of superfluidity

I'm trying to teach myself about superfluidity and I'm slightly confused on the ''two-fluid'' description. From what I understand, the superfluid is considered to be a mixture of two fluids, a ...
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What observables are indicative of BCS Cooper pair condensation?

What observables are indicative of BCS Cooper pair condensation? "Thought" experiments and "numerical" experiments are allowed. This question is motivated by the question Has BCS Cooper pair ...
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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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255 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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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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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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211 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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227 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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226 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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140 views

Specific Heat of Liquid Helium

At the lambda point, the specific heat of Liquid Helium diverges. After searching for a curve, I've found only measured curves. Is there a theoretical curve for this transition?
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1answer
438 views

What happens at lambda point?

When Boson gas approach lambda point (no matter from superfluid side or liquid side),the heat capacity tend to diverge, doesn't this mean that we can never drive the gas through lambda point?(cause we ...
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153 views

Ground state energy of Bose Einstein gas

I am wondering why BE gas ground state contribute no energy.if so, then dose it mean that if we drive the Bose gas to absolute zero,then it doesn't own any energy?
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Is there any other superfluid element except helium?

Is there any other superfluid element except helium? Everywhere we see and speak about superfluidity, we just speak about superfluid helium. but is't there any other element or material or system ...
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1answer
165 views

Why does the superconductivity hamiltonian have a µ term, while the superfluid does not?

In every discussion of SC and SF that I read (e.g. Simons), the SC Hamiltonian (BCS) has a $\epsilon_k - \mu$ in the kinetic part of the Hamiltonian, while the SF Hamiltonian has just a $\epsilon_k + ...
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BCS-BEC crossover

It would be really helpful if somebody could describe what does one mean by a BEC-BCS Crossover. I was going through articles available on the topic, but I was unable to grasp the gist of the topic.
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Precisely speaking, does photon become massive or the phonon become massive, due to Higgs mechanism in superconductor?

Consider the low-energy field theories of superfluids and superconductors. In superfluids, the spontaneous breaking of the order parameter's phase creates phonons as the massless Goldstone bosons.(...
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Superfluids (meaning, properties)

I am curious as to what a superfluid is? I have seen videos that say that they have zero viscosity, and I know that it means that there is no friction between the layers of the fluid. But what is its ...
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Superfluid across a temperature gradient

As I understand it, superfluids cannot sustain temperature gradients; specifically, if a gradient is introduced somewhere on the boundary of the superfluid, a "second sound" thermal wave propagates ...
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307 views

Running Euler's disk in a superfluid

I was considering the toy Euler's Disk, a video can be found here: http://www.youtube.com/watch?v=mVl2CBG_h2s I was interested in understanding the behavior of the disk particularly in vacuum and in ...
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119 views

How two prove the second sound velocity is $1/\sqrt{3}$ times than the first sound [closed]

From Landau two hydrodynamics model in superfluid, we have the result $c_1^2=\frac{\partial P}{\partial \rho}|_T$ and $c_2^2=\frac{\rho_s s^2 T}{\rho_n c}$. In the zero temperature limit, how to ...
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190 views

Superfluid rotating frame of reference

I'm currently studying a text about Bose-Einstein condensates (BECs) and vortices. When they want to study whether a vortex will be formed, they look at the fact wether it's enegetically favorable. ...
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Looking for a complete review of the BEC-BCS crossover

I'm looking for comprehensive review of the BEC-BCS crossover, both from a theoretical point of view, and from a experimental one. Even something at textbook level, but exhaustive, would be OK, but I ...
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How can we see that there is superconductivity/superfluidity in the boundary theory in the holographic principle?

For example in the models for holographic superconductors we can calculate the conductivity. Also there is an energy gap. I can understand that it describes a superconductor. However I have also heard ...
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141 views

Is a falling, perfect sheet of fluid possible to create?

This is a bit of an abstract question so I'll try explain this as best I can from the bottom up. I would like to know if it is possible to observe a sheet of fluid, much like a sheet of glass, ...
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1answer
170 views

Lev Landau's proof of molecular motion at absolute zero?

I am reading the book "The man they wouldn't let die" by Alexander Dorozynski, which is an biography of Russian theoretical physicist Lev Landau, and I have encountered this passage Absolute zero ...
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Do we have magnetic monopole? Is charge, according to yesterdays paper on Nature by Ray-Roukokoski-Kandel-Möttönen-Hall (30.01.14) quantized?

As everybody here knows, Maxwell's equation would look more beautiful if a magnetig charge were present. Beyond the aesthetics question, if a single magnetic Dirac monopole would be found, the ...
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467 views

Can a solid object float on a frictionless liquid?

Assuming the solid is less dense than the liquid, will a solid object float on a frictionless liquid? I can imagine that due to the pressure gradient the object will float, but I can also imagine ...
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Simple & intuitive explanation of superfluidity?

I know that superfluidity is caused by the fluid having zero viscosity. This only happens at very low temperature, so the fluid (e.g. Helium-4) is a Bose-Einstein condensate. I also know that in a ...
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How to understand the emergent special relativity in the superfluid?

The superfluid vacuum theory was proposed to understand some features of the vacuum (aether) from the emergence point of view. Although made up of non-relativistic atoms, the low-energy excitations of ...
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Bulk modulus of Liquid helium and first sound

Does anyone know where to find the bulk modulus of liquid helium ? I've been looking all over the internet but everywhere I get N/A. Any tips ? I'd need it to estimate the speed of first sound in ...
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Third-order topological quantum phase transition in p+ip superfluid

A two-dimensional spinless non-relativistic p+ip superfluid undergoes a quantum phase transition between the BCS (weakly-coupled) and BEC (strongly-coupled) regimes. This transition is driven by ...
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Superfluid Fountain

I was wondering how a super fluid fountain can flow indefinitely without violating energy conservation.
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What is off-diagonal long range order in superfluid?

From Wikipedia: [...]Off-diagonal long-range order (ODLRO) [...] exists whenever there is a macroscopically large factored component (eigenvalue) in a reduced density matrix of any order. How to ...
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Superfluidity and superconductivity?

Superfluidity and superconductivity? Is there any relation between the two aside from the fact that they are somewhat analogies , I see a lot of people on the internet who claim the helium (in it's ...
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Why aren't all quantum systems superfluids

Simply I was just wandering why aren't all quantum systems (F-D and BE condensates) superfluids at low temp like He 3 and 4?
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Why water is not superfluid?

My question is in the title. I do not really understand why water is not a superfluid. Maybe I make a mistake but the fact that water is not suprfluid comes from the fact that the elementary ...
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740 views

Symmetry breaking in Bose-Hubbard model

According to Landau's symmetry breaking theory, there is a symmetry breaking when phase transition occurs. What is the symmetry breaking of superfluid-Mott insulator transition in Bose-Hubbard model?...
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361 views

Microscopic Theory of superfluidity

In comparison with superconductivity what is the microscopic theory of superfluidity? Who has done it?
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periodic boundary conditions for vortex in a square lattice

I am trying to follow this paper and track the dynamics of vortex motion on a discrete (square) lattice. The idea is to simulate the time evolution of the Gross-Pitaevskii (GP) equation, which reads (...
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The bizarre behaviour of superfluids! Climbing up walls and geting out of glass beakers

SUPERFLUIDITY: Superfluidity is one of the most amazing quantum phenomena, which we can sit and watch them happening before our eyes! Watch this video, it is only a couple of minutes long, which ...