September 28, according to foreign media reports, scientists have recently made unexpected discoveries in the cold and dense helium-3 superfluid medium. Foreign matter passing through the medium can exceed the critical speed limit without destroying the fragile superfluid itself.
Since this contradicts our understanding of superfluid, this poses a problem. But now, by recreating and studying this phenomenon, physicists have figured out why. The particles in the superfluid will adhere to the foreign body, preventing the foreign body from interacting with most of the superfluid, thus avoiding damage to the superfluid.
Salim Otti, a physicist at Lancaster University in the United Kingdom, said: “For the steel rod passing through it, the helium-3 superfluid exists as if it were a vacuum, even though it is actually a relatively dense liquid. But there is no resistance. This is very interesting.”
Super fluid is a fluid with zero viscosity and zero friction, so it does not lose kinetic energy when flowing. Helium-4 bosons can become superfluids relatively easily. When the temperature is properly controlled and only slightly higher than absolute zero, the helium-4 boson can slow down to overlap to form a high-density atomic group, which can act as a “superatom.”
However, these “superatoms” are only one type of superfluid. Another type of superfluid is based on fermions, a compatriot of bosons. Fermions are particles that include atomic building blocks (such as electrons and quarks).
After cooling below a certain temperature, fermions will combine to form a so-called Cooper pair. Each Cooper pair is composed of two fermions, which together form a coincident boson. These Cooper pairs behave almost exactly like bosons, so they can also form superfluids.
Then, the research team used helium-3 to create a Fermi superfluid. Helium-3 is a rare isotope of helium, one less neutron than helium. When cooled to a temperature only a few millikelvins higher than absolute zero (-273.15 degrees Celsius), helium-3 will form a Cooper pair.
These superfluids are very fragile. If an object passes through the superfluid beyond a certain speed (critical Landau speed), the Cooper pair in it will split.
However, in a 2016 paper, researchers at Lancaster University discovered that a steel wire rod can pass through a helium-3 superfluid at a speed higher than the critical velocity without breaking the Cooper pair.
In their follow-up experiments, the researchers also measured the force required to pass the steel rod through the superfluid. When the steel rod started to move, they measured a very small thrust; but once the steel rod moved, the force to keep the steel rod moving became zero. In short, with a light push, the wire rod will move.
The research team finally concluded that the initial force comes from the Cooper pairs moving around the steel rod to adapt to the changing state, and these Cooper pairs exert a little starting force on the steel rod. However, after that, the steel rod can move freely, as if wearing Cooper’s camouflage coat.
“By changing the direction of movement of the steel rod, we can conclude that even if the speed of the steel rod is good, the steel rod can be hidden in the superfluid with the help of particles covering it,” Lancaster University Physics Said the expert Ash Jennings.
This new discovery may bring some interesting inspirations.
Fermi superfluid can be used to make superconductors, and superconductors are still under research and are an important part of quantum computers. Understanding the properties of superfluids helps us get closer to the goal of manufacturing superconductors.
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