June 21, 2010 FOR IMMEDIATE RELEASE A crack in the case for
supersolids Reports of supersolid helium may have been premature
Physicists have long known that helium can become a superfluid
at low temperatures, allowing it to flow completely friction
free, spontaneously climb walls, and exhibit other
counterintuitive characteristics. Based on quantum mechanical
calculations dating back to the 1970's, some physicists
predicted similar effects in solid materials. In particular,
they expected ultracold solid helium could become a mixture of
normal solid and supersolid forms. It wasn't until 2004 that
physicists were able to devise a way to look for supersolid
behavior in helium. They filled a hollow torsion pendulum (a
type of pendulum that rotates rather than swinging back and
forth) with helium, then measured the rate that it twisted as
the helium was cooled. Because the periodic twisting rate
depends in part on the amount of normal helium in the pendulum
cavity, they expected that the period would change if som