Supersolidity of helium-4: Disordered scenarios

The discovery of the phenomenon of supersolidity in helium, a non-dissipative transport of (4)He-atoms through (4)He-crystals, is an amazing achievement in the low-temperature physics. A microscopic interpretation of the phenomenon of non-classical rotational inertia originally discovered by Kim and Chan remains highly controversial. The only direct observation of a superflow through solid (4)He is the one reported recently by Ray and Hallock. First-principle simulations by Amherst-ETH-Alberta-CUNY collaboration, while unquestionably showing that a perfect hcp (4)He crystal is not a supersolid, reveal disordered mechanisms of supersoliclity: superfluid dislocations, grain boundaries, and ridges. Also possible is a metastable amorphous supersolid, the so-called superglass. (C) 2008 Elsevier B.V. All rights reserved.