Hi Chris,

While liquid helium is a prime example of a superfluid, supefluidity is a general term to describe a particular state that occurs in integer spin quantum systems. In neutron stars, this superfluidity is thought to occur from a form of "cooper pairs" of neutrons (each of which have half integer spin but when in a cooper pair state forms a integer spin system (1/2 + 1/2 = 1)).

Liquid helium (more precisely helium 4) is a superfluid because it has 2 neutrons and two protons, each with spin 1/2, which add up to a a net integer spin.

Spin in this case refers to the spin angular momentum quantum number.

Jonny

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