Physics, asked by Narutsu, 10 months ago

Is the superfluid liquid helium also related to a Bose Einstein Condensate (or is it a Bose Einstein Condensate)? Liquid helium does have its quantum particles all in the same quantum phases just like a Bose Einstein Condensate should and also acts like a combined mass. If it is a BEC, why is it called a superfluid?

Answers

Answered by rakhithakur

A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero(-273.15 °C). Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which point microscopic quantum phenomena, particularly wavefunction interference, become apparent macroscopically. A BEC is formed by cooling a gas of extremely low density, about one-hundred-thousandth the density of normal air, to ultra-low temperatures.

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rakhithakur: Key differences of helium superfluidity and BEC:

rakhithakur: Interactions: He-II is a practically incompressible liquid due to hard-core interactions, while the ideal BEC has no compressibility!

rakhithakur: Heat capacity vanishes as T^{3} at low temperatures, as opposed to T^{3/2} for BEC

rakhithakur: Differences in the superfluid fraction:

The superfluid fraction not vanish linearly at the transition point

The normal fraction does not vanish as T^{3/2} at zero temperature

There can be no superfluidity if the spectrum of excitations scales quadratically in momentum [cf Kelvin waves excited by wind on water]

These differences can be accounted for by the Landau spectrum of elementary excitations (phonons+rotons)

Answered by Marsmars

The mysterious behaviour of superfluid liquid helium can be explained by using Bose einstein condensation. Superfluidity and superconductivity is the two remarkable phenomena which manifest Bose einstein condensation..When 4helium(a boson) is cooled to lambda point (temperature at which transition to superfluid takes place) it Mark's the onset of Bose condensation. The properties of superfluid can be explained by using Bose statistics. When the liquid helium is in a rotating bucket and is condensed below the lambda point the fraction of condensed particles who is forced to have the same quantum state according to Bose statistics have to make choice between the two states and choices the non rotating state..as more and more particles condensed the superfluid liquid helium becomes at rest with respect to the surrounding. similarly the non viscous nature of superfluid can also be explained by using Bose statistics..since all have to occupy the same quantum state if it's been scattered by the wall of the container it has to done simultaneously.....

Even 3He also shows superfluidity at temperature lower than 4He ...its because 3He is a fermion ...so it have to obey fermi statistics rather than Bose statistics but when its cooled the electrons paired up to form a quasi molecular complex and behaves like bosons thus obeying Bose statistics

thus superfluidity is the consequence of Bose einstein condensation.......

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