A Helium Superfluid Wins Physics Prize

The 1996 Nobel Prize in physics was awarded today to David Lee and Robert Richardson of Cornell University and Douglas Osheroff of Stanford University for their discovery of an unusual liquid form of the isotope helium-3. The discovery opened up an unexplored world of microscopic interactions in the field of low-temperature physics.

For years physicists tried to coax helium-3 into a liquid state called superfluidity, in which a fluid has no viscosity--allowing it to flow nearly unimpeded through tiny pores--and in which it becomes an excellent heat conductor. The sticking point was that helium-3 atoms interact with each other in a way that prevents them from easily achieving a low-energy state, a necessary condition for superfluidity. While helium-4, the prevalent form of the isotope, becomes a superfluid a few degrees above absolute zero, the rarer helium-3 cannot.

But quantum mechanics, the set of equations governing the behavior of subatomic particles, as well as research on superconducting metals, suggested that helium-3 could in fact become a superfluid. The Cornell team hadn't even set out to find the superfluid, but around Thanksgiving in 1971 they noticed a serendipitous hiccup in their data on a mixture of solid and liquid helium-3. It took "8 months of very solid experimentation before we had a good idea of what the footprint of this thing was," Lee says. "It was a very enjoyable period. One beautiful thing after another happened in the laboratory."

Lee's team discovered that helium-3 atoms, at only a few thousandths of a degree above absolute zero, can pair together and behave like particles called bosons. This allows the atom pairs to slip into the same, low-energy state as helium-4 and become a superfluid.

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