The discovery that helium-3 at extremely low temperatures could become, like helium-4, a superfluid--having no viscosity whatsoever--earned David Lee and Robert Richardson of Cornell University and Douglas Osheroff of Stanford University a 1996 Nobel prize. But in fact, studying this wondrous substance since then has proved a bit tricky. Helium-4 becomes superfluid when pairs of its atoms condense into a coherent quantum state. (As such, with no resistance to flow, the fluid can pass where even a gas cannot.) Although helium-3 does the same, its atomic couples are magnetic, adding complications.

Scientists have typically examined the interactions between such helium-3 atoms by first putting fluid samples into aerogel--a superlight solid comprised of skinny silicon columns. The result is that the temperature at which this dirty helium-3 becomes superfluid drops. But researchers at the National Center for Scientific Research in Grenoble, France, report in the October 16 issue of Physical Review Letters that helium-3 acts somewhat superfluid at temperatures in between its normal and aerogel-influenced transition points. They studied the helium using nuclear magnetic resonance and suggest that perhaps the behavior of the atoms at these intermediate temperatures represents a new kind of superfluidity--a state in which four helium-3 atoms are joined instead of two.

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