Questions tagged [superfluidity]

A flow with no viscosity

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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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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 ...
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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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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 ...
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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. ...
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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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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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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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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 ...
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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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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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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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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 ...
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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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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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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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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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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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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 ...
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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 ...
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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 ...
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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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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 ...
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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 ...
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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 ...
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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. ...
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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-...
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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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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 it’s even true, that is)?
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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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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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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 ...
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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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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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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 ...
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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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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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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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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 ...
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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? ...
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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 ...
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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 ≤ 2. And Goldstone bosons ...
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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 ...
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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 ...
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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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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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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. ...
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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 ...
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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 ...
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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 ...