Frozen helium-4 behaves like a combination of solid and superfluid
Researchers at the Pennsylvania State University are announcing the possible discovery of an entirely new phase of matter: an ultra-cold, "supersolid" form of helium-4.
Writing in the 15 January 2004 issue of the journal Nature, Penn State physicist Moses H. W. Chan and his graduate student, Eun-Seong Kim, explain that their material is a solid in the sense that all its helium-4 atoms are frozen into a rigid crystal lattice, much like the atoms and molecules in a normal solid such as ice. The difference is that "frozen," in this case, doesnt mean "stationary." Because helium-4 lattice is so very cold, less than one tenth of a degree above absolute zero, the laws of quantum uncertainty take over. In effect, the helium atoms start to behave as if they were both solid and fluid--at the same time. Under the right circumstances, in fact, some fraction of the helium atoms can begin to move through the lattice like a substance known as a "superfluid": a liquid that moves with no friction whatsoever. Thus the name "supersolid."
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