At temperatures below 2.176K, liquid He-4 enters into a superfluid state and flows without any friction. The onset of superfluidity is associated with Bose-Einstein condensation where the He-4 atoms, which are bosons, condensed into a single momentum state and acquire quantum mechanical coherence over macroscopic distances. Recent torsional oscillator measurements of solid helium confined in porous media [1,2] and in bulk form [3,4] found evidence of non-classical rotational inertia indicating superfluid behavior below 0.2K. Measurements of solid samples at different pressure (and hence different density) allow us to map out the boundary of this supersolid phase. This work is done in collaboration with Eunseong Kim, Tony Clark, Xi Lin and Josh West and it is supported by the (U.S.) National Science Foundation.
1. E. Kim and M.H.W. Chan, Nature 427, 225 (2004).
2. E. Kim and M.H.W. Chan, Jour. of Low Temp. Physics, 138, 859 (2005).
3. E. Kim and M.H.W. Chan, Science 305, 1941(2004).
4. E. Kim and M.H.W. Chan, Phys. Rev. Lett. 97, 115302 (2006).
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