High Temperature Mobility in Solid 4-Helium

Can solid helium support superflow? This 40 year old question seemed

to have been answered positively in 2004 when Kim and Chan [1] discovered

that some of the mass of solid helium inside a torsional oscillator

decoupled from the walls. This effect showed up at temperatures below

0.2K. However, newer experimental results and theoretical calculations

give several other possible explanations to the observed results,

and the physical mechanism responsible for the apparent

mobility of solid helium still remains a subject of intense study.

We performed similar torsional oscillator experiments [2] on solid helium at temperatures

an order of magnitude higher. We observed mass decoupling of

around 30%, which appeared only after

disorder was introduced into the crystal. Our results show many other

features similar to the low temperature results yet consistent with

a non superfluid origin of the phenomenon. Dislocation dynamics is

one possible alternative explanation.

[1] E. Kim and M. H. W. Chan, Nature 427, 225 (2004)

[2] A. Eyal, O. Pelleg, L. Embon and E. Polturak, Phys. Rev. Lett. 105, 025301 (2010)