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For the first time, researchers have documented the long-predicted occurrence of 'walls bound by strings' in superfluid helium-3. The existence of such an object, originally foreseen by cosmology theorists, may help explaining how the universe cooled down after the Big Bang. With the newfound ability to recreate these structures in the lab, earth-based scientists finally have a way to study some of the possible scenarios that might have taken place in the early universe more closely.
The findings, to be published 16th January in Nature Communications, came after two successive symmetry-breaking phase transitions at Aalto University's Low Temperature Laboratory.
Helium - Liquid - Pressure - Materials - Helium
Helium stays a liquid at atmospheric pressure even when chilled down to absolute zero, at which all other materials freeze solid. Not only does helium remain fluid at cryogenic temperatures, but it becomes a superfluid at a sufficiently low temperature. A superfluid material has essentially zero viscosity, which means it should flow forever without losing energy.
When confined to a nano-structured volume, researchers can use superfluid phases of the isotope helium-3 to study effects like half-quantum vortices—whirlpools in the superfluid where the amount of helium flowing is strictly controlled by the rules of quantum physics.
Vortices - Temperature - Vortices - Sample - Millikelvin—instead
"We initially thought that the half-quantum vortices would disappear when we lowered the temperature. It turns out that they [half-quantum vortices] actually survive as the helium-3 sample is cooled below half a millikelvin—instead a nontopological wall appears," says Jere Mäkinen, lead author of the study and doctoral student at Aalto University.
While not physical walls, which would...
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