Supersolidity ?

The so-called supersolidity has fascinated experimentalists for several years. Suppose one cools down an amount of Helium4 under huge pressure to solidify it. Some dizzying phenomena might happen: the as-solidified crystal shows a considerable decrease in friction. A a group from Japan and Korea did recently an experiment that supports the existence of supersolidity [DOI: 10.1126/science.330.6007.1033-a ].

Now, Kim, Kimitoshi Kono of Japan's research institute RIKEN in Wako, and colleagues have performed a torsional oscillator experiment in a specialized refrigerator, or “cryostat,” in which they can spin the whole experiment at speeds up to a revolution per second. Working in Kono's lab, they found that as the rate of rotation increased, the shift in the frequency that supposedly tracks the resistance-free flow decreased and eventually vanished.

That's what should happen if the flow is real. Thanks to quantum mechanics, a superfluid abhors rotation. Spin a bucket of superfluid liquid helium, and the liquid will sprout tiny whirlpools called “vortices” spinning to counteract the rotation. Put a torsional oscillator in a spinning fridge, and vortices will tie up the superfluid, leaving less to stand still and reducing the frequency shift seen as superfluid flow sets in. Kim's result suggests that rotation stirs up vortices in solid helium, too, says Sébastien Balibar, a physicist at the École Normale Supérieure in Paris.