Does a superfluid have zero viscosity or zero surface tension or both?
Does not zero surface tension guarantee creeping against gravity? if so, then why Wikipedia mentions only zero viscosity? ( https://en.wikipedia.org/wiki/Superfluidity )
How does spin-pairing of two atoms make them immune to attraction or repulsion from bulk surface? can this be explained in slightly simplified semi-classical terms?
{ like superconductivity is low temperature perfect coupling between electron wave and lattice wave(phonon) that makes cooper pairs? and classically, if the lattice distortion of lattice positive charges towards the negative charges are strong enough, then another negative charge,( i.e. another electron) can be brought near the first electron and the pair will go unimpeded through the superconductor since lattice deformations are at perfect harmony with the pair and do not collide with it}
and finally, like high temperature superconductivity, is high temperature superfluidity also possible? if yes, then how?
Note my depth of knowledge of quantum mechanics is still not too much
Zero viscosity sounds right, but offhand it seems to me you need surface tension to climb against gravity. (ie. you need another force).
People agree that the phenomena is a macroscopic manifestation of QM associated with Bosons (integer spin components) in this case liquid helium.
The the theory from statistical mechanics and QM is quite complex and still studied.
A superfluid is a macroscopic quantum state that has zero viscosity. For the helium film dripping out of a beaker above the bulk fluid this is a necessary condition because the flowing helium film is only a few hundred Angstroms thick, the viscosity of a normal fluid would stop any flow in such a thin film. The flow is driven by the gravitational potential energy difference for the beaker a height h above the helium, delta E = rho*g*h. He4 has a superfluid transition temperature of 2.176 K, but superconductors (which are also superfluids with zero viscosity for electron flow) can have much higher T_c values, now up to temperatures above 200 K for very specialized materials under Gigabar pressures. There are also now BEC magnon (spin) systems in ferromagnetic materials that have been found to be superfluid at room temperature and above.
Superfluidity is possible for a gas of quasiparticles called Rotons (in helium 4) at very low temperatures, also as Prof Williams suggested for quasiparticles called Cooper Pairs in High Tc Superconductors and more recently for quasiparticles called magnons at higher temperatures. Most of superfluidity research is carried for helium 3 and helium 4 at very low temperatures and high pressures. The unconventional pairing make it possible. Look at the pioneer works by Kapitza, Landau and Feynman among others scientists.
Dear Sumit,
The superfluidity is a Bose-Einstein-Condensation (BEC) of atoms as bosons.
High temperature superfluidity is impossible (at least at ambient pressure), because the temperature of BEC (Tbec) is roughly related to the atom density and inversely related to the atom mass. So Helium - 4 shows a limit of Tbec, since all other atoms are bigger and heavier than Helium.
High temperature superconductivity is possible, since the boson mass is equal to the mass of two electrons, i.e. much less than the Helium atom mass. A bit more about the matter in the short comment about room temperature superconductor Preprint Local Pairing and Room Temperature Superconductivity
An explanation in simpler words - which might not be quite right!
Superfluidity is something that is possible with bosons. These have integer spin (-1, 0, 1) etc and the laws of physics (just what they are!) mean that these particles can all share the same state, and become indistinguishable. This fundamentally changes the behaviour of the group so that it is quantum-mechanical over a large scale, which results in behaviour that seems strange to us. Individual bosons in the state can't have interactions by themselves that cause friction, so there is no viscosity (not even just a little bit, but none at all).
The quantum mechanical wave describing the fluid can see the possibility of lower energy by being outside of the flask, so it can go there! This is not possible with fermions, with extra half spin, which all have to be in different states and can individually lose energy, resulting in viscosity and resistance, for instance.
Fermions can in some situations find it energetically advantageous to join together in pairs of opposite spin to make a boson. A sea of bosons can be a superfluid, or make a superconductor.
Dear Sumit Bhowmick , thinking about your interesting thread, I remember that the transverse localization scheme for light (photons) can happen at higher temperatures. I don't know if transversal light localization is a coherent quantumechanical state or only a localized state. Although it is not a superfluid (macroscopic), it is---a spin one---photon transition observed experimentally.
Article Transverse Anderson localization of light: A tutorial
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