Its fundamental interest lies in the manifestation of quantum mechanics on macroscopic length scales – for example quantisation of angular momentum. This implies that superfluid helium contained in a torus remains stationary if the torus is rotated slowly. In 2004 it was shown that below 0.2 K, ~2% of the mass of solid helium contained in a torus similarly does not rotate when the torus is rotated! It has been proposed that Bose Einstein condensation (BEC), which is responsible for superfluidity, is also responsible for ‘supersolidity’. BEC in the liquid gives a sharp drop in atomic kinetic energy and spaces develop in the liquid structure. In contrast a VESUVIO experiment observed no change in the structure or kinetic energy of the crystalline solid, suggesting that BEC does not occur. This kind of experiment requires special high pressure and ultra-low temperature sample environment. ISIS user support group developed the experimental apparatus for the Vesuvio experiment, together with the experimental procedure used for growing a controlled quality solid 4He sample.
MA Adams, J Mayers, R Done, M Chowdhury, RBE Down, OI Kirichek (ISIS)
Research date: December 2007
MA Adams et al., Phys. Rev. Lett. 98 (2007) 085301