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Superfluidity in
4He (bosons)
occurs because most 4He atoms gather in the
lowest quantum state (Bose-Einstein
condensation).
The 3He atoms are fermions
and should not be able to condense. Yet we know
from superconductivity that electrons, which
are also fermions, can become bosons by pair
formation. The same turned out to be true also
for 3He
atoms. At about 2 mK they form pairs and become
bosons. Bose-Einstein condensation occurs and
3He becomes
superfluid.
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