If you were to put an object on a rotating turntable you would expect the object to be dragged round; but what if the turntable were made of solid helium-4? The answer is perhaps surprising. According to the prediction made by A F Andreev and I M Lifschitz in 1969, the turntable would keep turning without affecting the object. Dubbed "nonclassical rotational inertia", or NCRI, this failure of friction was observed in superfluid liquid helium back in 1967. Now, for the first time, the analogue has been seen in a solid.
E Kim and M H W Chan of Pennsylvania State University made the tricky measurements at a chilly 230mK and confirmed the prediction of Andreev and Lifschitz. A detailed interpretation of the underlying physics is still not complete, but it could be linked to a Bose-Einstein condensate in the solid and could revolutionize theories of solid helium.
Further reading
E Kim and M H W Chan 2004 Science 305 1941.
Author:
Compiled by Steve Reucroft and John Swain, Northeastern University