Superfluidity is a phase of matter or description of heat capacity in which “unusual” effects are observed when liquids, typically of helium-4 or helium-3, overcome friction by surface interaction when at a stage, known as the “lambda point ” for helium-4, at which the liquid’s viscosity becomes zero. Also known as a major facet in the study of quantum hydrodynamics, it was discovered by Pyotr Leonidovich Kapitsa, John F. Allen, and Don Misener in 1937 and has been described through phenomenological and microscopic theories.