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Recently, scientists have made unexpected discoveries in the cold and dense medium of helium-3 superfluid that foreign objects passing through the medium may exceed the critical speed limit without breaking the superfluid state.
This contradicts our long-term experience, so it is a problem that needs explanation. However, physicists have now figured out the truth. It turns out that the particles in the superfluid will adhere to the object and wrap around it so that it cannot interact with the superfluid as a whole, therefore it will avoid the collapse of the superfluid.
Super fluid is a fluid with zero viscosity and zero friction, so it does not lose kinetic energy when flowing. The boson of the helium 4 isotope can be used to create a superfluid relatively easily. As long as it is cooled to just above absolute zero, the low temperature slows down the oscillation of the atoms, thus the overall synchronization and the formation of high-density atomic clusters causes all atoms to behave as a "super atom".
In addition, there are superfluids based on fermions. Fermions are particles that include atomic building blocks, such as electrons and quarks.
When cooled below a certain temperature, fermions combine to form a so-called Cooper pair. Each Cooper pair is composed of two fermions, which together forms a composite boson. These Cooper pairs behave exactly like bosons, so they can form superfluids.
The team used helium 3 to create a Fermi ion superfluid, a rare isotope of helium, one neutron less than helium 4. When helium 3 is cooled to only 0.0001 Kelvin above absolute zero, a Cooper pair is formed.
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These superfluids are very fragile. If an object passes through it at a certain speed (called the critical Landau speed), the Cooper pair will break.
However, in 2016, researchers at Lancaster University discovered that wires passing through the helium 3 superfluid can exceed the critical speed without destroying the superfluid.
In the subsequent experiments, they measured the force required to pass the wire through the superfluid. When the wire starts to move, there will be a very weak hindering force. But once it starts to move, the required thrust is zero.
In the beginning, when the wire was inserted, the Cooper pair had to be pushed away, so the resistance was measured. When the Cooper pair in the superfluid covers the foreign object, for the superfluid, the moving mass is the superfluid itself, so the stability of the superfluid will not be damaged by the interaction.
Iron ion superfluid can be used to make superconductors, and superconductors are an important part of quantum computers. Knowing more about the mechanism of superfluid may bring us closer to the final application goal.
The research is published in Nature Communications.