Questions tagged [superfluidity]

A flow with no viscosity

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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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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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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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Can you put a magnetic ball into a hollow magnetic sphere? Ask Question Asked $7$ years, $7$ months ago? New Material Encasement [closed]

It was mentioned that certain rare earth magnetic needed to be created needing a separate space for transfer of energy. Or a more appropriate manner of containment the energy within a sphere of ...
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What is so topological about topological phase transitions?

I am studying the KT-transition, which is called a topological phase transition. The phase transition is driven by vortices in a 2-D superfluid, where it is shown that at a critical temperature $T_c$ ...
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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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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 ...
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What is the Difference between a Lepton and a Fermion?

As the Title Says: I am Wondering what the Difference between a Lepton and A Fermion is. I know they both have an ½ integer spin number e.g. a electron, an atom with an odd mass number such as Helium-...
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How can I measure air velocity in a pipe, exceeding 500 MPH? [closed]

Some details: I am designing a convergent divergent nozzle to accelerate exhaust gas in a pipe to supersonic speeds. I have the math figured out. However, once my prototype is complete, I am ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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 ...
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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 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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Diamagnetic current in the BdG superconductor

Recently, I am following the paper arXiv:1610.01803 to study superfluid weight. In this paper the diamagnetic current is given by: $j^D_{\mu}(\vec{q})=\sum_{\vec{k},\sigma}\partial_{\mu}\partial_{\...
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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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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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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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Would an airplane flying through superfluid helium experience lift and drag?

Would an airplane flying through superfluid helium experience lift and drag? The airplane is presumed cold enough to not heat up the helium.
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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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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 ...