Questions tagged [superfluidity]

A flow with no viscosity

Filter by
Sorted by
Tagged with
0 votes
0 answers
18 views

Why superfluid He-4 exhibits one degree of freedom zero viscosity but when for example rotated has a non-zero viscosity?

It is shown clearly in this demonstration that He-4 superfluid has zero viscosity for a one directional flow (i.e. one degree of freedom in motion) but shows viscous behavior when a more complex ...
user avatar
  • 3,035
3 votes
1 answer
75 views

How the concept of "wave function of atom" in Bose-Einstein condensate should be interpreted from perspective of quantum field theory?

A typical description of Bose-Einstein condensate goes along the line of "multiple atoms in the same ground state can be described by the same wave function". But hold on. Atoms are not ...
user avatar
1 vote
1 answer
32 views

Excitations of Neutral Superfluids and their Interactions

I need some clarifications about the low energy excitations superfluids and their interactions. First case, Bose superfluid: As far as I know, there are 3 kinds of commonly known excitations in this ...
user avatar
  • 990
0 votes
0 answers
29 views

Fluid in a Rotating Cube

Fluid in a rotating cylinder has a paraboloid shape. But, I was wondering what shape would the liquid take in a rotating cube. If possible, explain mathematically.
user avatar
0 votes
1 answer
19 views

Cryogenic Particle Detectors

Recently, I started reading about Neutrinos, their types, oscillations and their detection. Today many experiments are being conducted to detect and measure oscillations of sterile neutrinos and anti-...
user avatar
1 vote
0 answers
28 views

Do inviscid fluids have thermal conductivity?

Inviscid fluids are an idealization and they don't have viscosity. The no-slip boundary condition DOESN'T apply to them and consequently, these fluids won't display a hydrodynamic boundary layer. I've ...
user avatar
2 votes
0 answers
44 views

What role do quantized vortices play from the Superfluid model in Superfluid Vacuum Theory?

When rotating a superfluid (such as $^{4}$He) below its critical temperature, sometimes quantized vortices pop up, depending how fast one rotates this superfluid. In the SVT model, they propose that ...
user avatar
0 votes
0 answers
18 views

Thermal boundary layer of an inviscid fluid

We know that an inviscid fluid flowing along a flat plate doesn't develop a hydrodynamic boundary layer because there is no friction. we also know that viscosity is caused by intermolecular forces and ...
user avatar
1 vote
0 answers
36 views

How does all of the superfluid empty from the beaker?

From what I understand, a superfluid is comprised of its normal fluid component and superfluid component (Landau's two fluid model). This normal fluid component has viscosity. What I don't understand, ...
user avatar
3 votes
1 answer
352 views

Why do "quantum vortices" form in superfluids?

I've been reading up on Superfluids, and they've fascinated me. I understand why their superfluid component has zero viscosity, but there's one aspect that's bothering me, and that's the formation of ...
user avatar
2 votes
0 answers
31 views

Qualitative difference of excitations in Fermi VS Bose superfluids

Assume that we have an electrically neutral interacting gas (or liquid) of Bose or Fermi particles in a superfluid state. For simplicity, assume that the particles interact via an assigned central ...
user avatar
  • 2,896
1 vote
0 answers
23 views

Connection between superfluid density and spin stiffness

I am currently trying to understand the apparent equivalence between spin stiffness and superfluid density. I (think I) understand how the XXZ model maps onto the Boson-Hubbard model with the ...
user avatar
  • 207
0 votes
0 answers
36 views

How do we know that helium is a liquid at absolute zero?

I was looking at a phase chart of helium and like many before me, I was surprised that helium was a liquid at absolute zero: Now there are plenty of explanations online for why it can be liquid ...
user avatar
2 votes
0 answers
59 views

Nambu-Goldstone mode without symmetry breaking

Superfluidity is often explained in terms of spontaneous breaking of global $U(1)$ symmetry. However, we know that in real, finite-size quantum systems, this symmetry can never be broken. Quantum ...
user avatar
  • 6,238
0 votes
1 answer
24 views

Capillary action in presence of weight and atmospheric pressure

In capillary action the water for example rises in a small-diameter-glass tube due to that the cohesive and adhesive forces are larger than gravity and fall if they were less than gravity .The ...
user avatar
0 votes
0 answers
60 views

Double slit experiment on superfluid surface. What do we observe?

What do we observe when we perform a double slit experiment with mechanical waves on the surface of a superfluid? Do the ripples on the superfluid form and propagate similar to ones on water? What ...
user avatar
  • 690
1 vote
0 answers
33 views

Will the water level keep rising up after attaining terminal velocity?

Suppose I have an infinitely long container of water and I dropped a metal ball into it. Initially, the water level will rise up due to displacement of volume. But will it keep rising when the whole ...
user avatar
  • 153
2 votes
1 answer
52 views

Connection between superfluidity and temperature

I don't understand the significance of temperature in relation to the presence of superfluidity. Why, in general, are low temperatures necessary?
user avatar
4 votes
1 answer
121 views

Is a vortex crystal a supersolid?

Reading the article [Rev. Mod. Phys. 84, 759 (2012)] by Prokof'ev and Boninsegni, a supersolid is defined as a homogeneous phase of matter in which both density long-range order (i.e. ordered spatial ...
user avatar
2 votes
1 answer
69 views

How $^3\text{He}$ atoms remove thermal energy from surrounding environment in dilution refrigerator?

I am trying to understand how a dilution refrigerator works. I understand that $^3\text{He}$ atoms are pumped out of the diluted phase and to reestablish an equilibrium, new $^3\text{He}$ move there ...
user avatar
0 votes
1 answer
105 views

Difference between BEC and Superfluidity. Why is considered superfluid helium not a BEC?

I have not a clear idea what the difference between a BEC of weakly interacting bosons and superfluid is. My second question that could help me understand this difference is: why do alkali atoms form ...
user avatar
  • 1
0 votes
0 answers
26 views

How is the climbing effect of superfluid Helium related to the Classius-Clapeyron relation?

From the Wikipedia article of Helium-4 (emphasis by me). For example, if superfluid helium-4 is kept in an open vessel, a thin film will climb up the sides of the vessel and overflow. In this state ...
user avatar
2 votes
0 answers
21 views

Does superfluid have substructure? I mean does the substructure matter?

My main research interest is the gravitational wave. Recently, I and my academic brother watched a famous video about the superfluid. I read a review then came up with some questions. Here is the ...
user avatar
1 vote
0 answers
31 views

Quantum vs Classical Vorticities

Excepting the circulation quantization, what are the differences between classical vorticities (created in classical fluids) and quantum vorticities (BEC superfluids)?
user avatar
  • 313
1 vote
1 answer
39 views

How does particle-particle interactions affect superfluids?

Ive read that London approach of superfluidity was wrong because he took them as non-interacting bose gas molecules and got incorrect temperature dependence for density, but also one can take ...
user avatar
  • 63
2 votes
1 answer
102 views

Problems met in Matsubara frequency sum

I would like to calculate $\sum\limits_{\omega_{n},\vec{k}}(\ln(-i\omega_{n}+\xi_{\vec{k}})+\ln(-i\omega_{n}-\xi_{\vec{k}}))$, where $\omega_{n}=\frac{2n+1}{\beta}$ and $n=0,\pm1,\pm2,\dots$ Using the ...
user avatar
  • 592
1 vote
0 answers
32 views

Matsubara sum in mean field theory of superfluid

Ths system is given in Doppler shift in current-carrying superfluid. Here to make mean-field theory, we set $\vec{Q}=0$ and $\Delta(x)=\Delta_{0}$. After some manipulations, we obtain the ...
user avatar
  • 592
0 votes
1 answer
32 views

Superfluid + Super conductivity in a bose condensate

so my question is this can we theoretically and empirically find a BOSE condensate, with SUPERFLUID properties but which is also a SUPERCONDUCTING device ?
user avatar
1 vote
2 answers
329 views

Why the electric field inside a superconductor is always zero?

Recently I have been reading the book called "Superconductivity, Superfluids and Condensates" from James F. Annett. I was confused by the expression that zero electric field at all points ...
user avatar
2 votes
2 answers
221 views

Superfluid condensate wave function

I am reading Girvin's Modern Condensed Matter Physics and I have a question about the off-diagonal long-range order (ODLRO). In chapter 18.1, he starts from \begin{align} \rho(\vec{r},\vec{r}') = \...
user avatar
  • 691
1 vote
1 answer
35 views

Lagrangian for a fixed number of non-interacting, non-relativistic bosons

In my book on QFT, (during an explanation of superfluidity) the author states that the lagrangian for a fixed number of non-interacting, non-relativistic bosons is $$i\Phi^{\dagger}\partial _{0}\Phi-\...
user avatar
  • 43
2 votes
0 answers
64 views

Ginzburg-Landau and Coherence Length

Consider the Ginzburg-Landau functional for a complex function $\psi:\mathbb{R}^3 \to \mathbb{C}$, i.e., $$ F[\psi]=\int \frac{1}{2M}|(-i\hbar\nabla -eA)\psi|^2+r|\psi|^2+\frac{u}{2}|\psi|^4 + \frac{B^...
user avatar
  • 1,618
2 votes
1 answer
162 views

Ground state of composite and non-interacting bosons on a lattice

Background Consider a lattice system described by the Hamiltonian $$ H = - J \sum_{\left\langle ij \right\rangle} \left( \Delta^{\dagger}_i \Delta_j + \mathrm{h.c.} \right) $$ where $\Delta_i$, $\...
user avatar
  • 1,551
2 votes
1 answer
74 views

Conceptual doubt in Superfluidity

I'm trying to understand superfluidity from these Caltech notes on Advanced Statistical Physics (Week 1, Section IV: Landau Criterion for Superfluidity) - So far it is not clear why a moving ...
user avatar
6 votes
1 answer
233 views

BCS pairing and BEC pair between Fermions

In many lecture notes, it points out We can tune the scattering length, using Feshbach resonance, to realize crossover from BCS to BEC in degenerate Fermi gases. When the scattering length is ...
user avatar
  • 592
4 votes
1 answer
231 views

Why is the surface integral ignored when deriving the current equation from Ginzburg-Landau theory?

The Ginzburg-Landau free energy is defined as $$F = \int dV \left \{\alpha |\psi|^2 + \frac{\beta}{2}|\psi|^4 + \frac{1}{2m^*} \left| \left(\frac{\hbar}{i}\nabla - \frac{e^*}{c}\vec{A}\right)\psi \...
user avatar
0 votes
1 answer
60 views

Why cannot calculate the gapped Higgs mode in superfluid?

According to Ch. 4.2 in Quantum Field Theory in Condensed Matter Physics by N.Nagaosa, when we deal with superfluid problem, bosonic field can be decompose into amplitude and phase: $$\begin{array}{l}\...
user avatar
  • 1,472
1 vote
0 answers
87 views

Confusion 1D Bose-Hubbard Model Field-Theory

The General Setting I have some confusion concerning the interpretation of the field-theory describing the Bose-Hubbard Modell especialy in the one dimensional case. The general framework of the ...
user avatar
  • 558
7 votes
1 answer
710 views

Superfluid Stiffness Definition

I am currently reading S. Sachdevs Book on Quantum Phase Transitions focusing on the Bose-Hubbard Model (Chapter 9) and especially the Dilute-Boson Field Theory (Chapter 16). When describing the fluid ...
user avatar
  • 558
2 votes
1 answer
57 views

Negative critical exponent $\alpha$ for Superfluid helium at lambda point

Due to the positive critical exponent of the transition in liquid helium I would expect there to be no peak at the transition $t=0$. Since the $t$ dependent part of the specific heat should go to 0 as ...
user avatar
  • 691
1 vote
0 answers
50 views

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 ...
user avatar
1 vote
0 answers
56 views

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 ...
user avatar
2 votes
1 answer
36 views

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 ...
user avatar
3 votes
1 answer
88 views

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. ...
user avatar
  • 2,896
1 vote
1 answer
75 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}=\...
user avatar
  • 592
2 votes
1 answer
274 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 ...
user avatar
  • 433
1 vote
1 answer
95 views

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. ...
user avatar
  • 488
5 votes
2 answers
1k views

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 ...
user avatar
1 vote
0 answers
87 views

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 ...
user avatar
  • 31
3 votes
0 answers
32 views

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{...
user avatar

1
2 3 4 5