superfluidity

superfluidity, the frictionless flow and other exotic behaviour observed in liquid helium at temperatures near absolute zero (−273.15 °C, or −459.67 °F), and (less widely used) similar frictionless behaviour of electrons in a superconducting solid. In each case the unusual behaviour arises from quantum mechanical effects. The stable isotopes of helium are helium-3 (or ³He), with two protons and one neutron, and helium-4 (or ⁴He), with two protons and two neutrons. ⁴He forms the bulk...