Evidence of Supersolidity in Rotating Solid Helium

Abstract

Supersolidity in a Spin Observing superfluid flow in a solid is a counterintuitive finding that has been accomplished by freezing 4 He inside a torsional oscillator and monitoring the oscillating period as the temperature is lowered: A reduction in the oscillating period will be observed at the supersolid transition when the mass of the superfluid decouples from the oscillator and the remaining normal component of the solid. However, extraneous classical effects can also cause this reduction, and so, to confirm supersolid formation, Choi et al. (p. 1512 , published online 18 November) performed a slightly different measurement. Rotation was superimposed onto the oscillating motion, and the period and the shear modulus of the system were measured simultaneously. These two quantities exhibited very different responses to the rotation speed, suggesting that supersolidity (rather than classical effects that would also affect the shear modulus) is indeed at the root of the previously observed change in the oscillating period.