Superfluid Strangeness

At ultralow temperatures, matter plays exotic physical tricks that fascinate physicists and offer insights into its fundamental nature. At 50 billionths of a degree above absolute zero (about -460 degrees Fahrenheit), matter can become "superfluid," flowing without friction. Even more strange, superfluid matter placed in a container would spontaneously rise up the sides and flow over the top.

New insight into such superfluid behavior came in a paper published January 27 in the online version of Science by Duke physicist John Thomas and his colleagues. They cooled a cloud of lithium atoms to ultralow temperatures and precisely measured how it responded to measured additions of heat energy. They observed evidence of a transition to superfluid.

What was striking about the finding was that lithium is a so-called "fermion," a class of atoms known to repel one another. Another class of friendlier atoms, called "bosons," readily form a superfluid. In becoming a superfluid, however, the lithium atoms appear to partner with one another, and this cozying-up enables the "phase change" to the exotic superfluid state.

Besides yielding basic insights into matter at extreme temperatures, the studies offer insight into what is called high-temperature superconductivity, in which materials offer no resistance to electricity at such balmy temperatures as -321 degrees Fahrenheit--the temperature at which nitrogen becomes a liquid. Thomas says that the kind of superfluidity they observed can be used to model superconductors that could conduct electricity without resistance at room temperatures or higher--long sought after by scientists. It could model such "hot" superconductivity even though the superfluid carries no electrical current as a real superconductor would. "But, in an analogous way, the particles flow without friction," he says.