Superfluidity is a phase of matter characterized by the ability of a fluid to flow with zero viscosity. This means that a superfluid can flow without dissipating energy, allowing it to move through small openings and along surfaces without friction. The phenomenon is most commonly observed in liquid helium at very low temperatures, specifically in helium-4 (He-4) and helium-3 (He-3).
Alfred Leitner - Liquid Helium II the Superfluid by Alfred Leitner (1963)
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