Scientists have found an unexpected finding in the frigid, thick medium of a helium-3 superfluid. The delicate superfluid might be broken by an outside item moving through it faster than a crucial speed limit.
This provided a significant challenge since it goes against our knowledge of superfluidity, but physicists have recently solved it by simulating and examining the phenomena. The superfluid's particles adhere to the item, protecting it from contact with the superfluid in bulk and avoiding decomposition.
"Although superfluid helium-3 is a rather thick liquid, a rod travelling through it experiences it as a vacuum. There is absolutely no resistance "explained Samuli Autti, a physicist at Lancaster University in the UK. This is quite fascinating to me.
Superfluids are a special kind of fluid that flow without losing kinetic energy because they have no friction and no viscosity. They may be created quite simply using the bosons of the helium-4 isotope, which, when chilled to a temperature just above absolute zero, slow down enough to overlap and form a high-density cluster of atoms that function as one "super-atom."
However, there is only one kind of superfluid formed by these "super-atoms." Another is based on the fermion, the boson's sister. Atomic building components like electrons and quarks are included in the class of particles known as fermions.
Fermions produce Cooper pairs, which are composed of two fermions that together make a composite boson, when they are cooled below a particular temperature. Due to the fact that these Cooper pairs behave precisely like bosons, they can create superfluids.
Helium-3, an extremely uncommon form of helium with one neutron missing, was used by the researchers to make their fermionic superfluid. Helium-3 generates Cooper pairs when chilled to one tens of a degree above absolute zero (0.0001 Kelvin, or -273.15 degrees Celsius/-459.67 degrees Fahrenheit).
Given the relative fragility of these superfluids, an item passing through them at a speed greater than the critical Landau velocity may cause the Cooper pairs to disintegrate.
Yet in a 2016 publication, Lancaster University researchers discovered that a wire rod travelling through a helium-3 superfluid could go faster than this speed without destroying the pairs.
They measured the force necessary to propel the wire rod through the superfluid in their subsequent tests. When the wire first began moving, they measured a very minimal force, but after it had begun moving, there was no longer any force needed to keep it moving; all it needed was a little prodding to get going.
The researchers came to the conclusion that the Cooper pairs' little movement to account for the motion, which applied a modest beginning force on the wire rod, is what causes the first force. However, following that, the wire is effectively covered in a coat of Cooper pairs and is free to move.
According to Lancaster University physicist Ash Jennings, "by changing the rod's direction of motion we were able to deduce that the rod will be concealed from the superfluid by the bound particles covering it, even when its speed is extremely high."
This new discovery could have some intriguing ramifications.
Superconductors can be produced using fermionic superfluids, and these superconductors are being researched as a key part of quantum computers. It seems probable that learning more about the mechanisms behind the behaviour of superfluids will only advance our understanding of it.
Nature Communications has published the study.
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