Is Solid Helium Supersolid ?

Orateur : Ariel HAZIOT [The Pennsylvania State University]

Thanks to its quantum properties, it has been proposed that superfluidity could coexist in the crystalline order of solid helium, thus forming a “supersolid“. During almost ten years, sever al groups in the world thought they had observed this paradoxical property named “supersolidity”. But nowadays, we understand that these crystals were not supersolid but instead the mobility of their dislocations is so high in the low temperature limit and if all impurities are suppressed, that it does not resist to shear stresses in some directions. The discovery of this "giant plasticity" in helium crystals is not less interesting than supersolidity. Its careful study has led to fundamental progress in the knowledge of dislocation networks and dynamics, which are basic phenomena at the origin of the plastic properties of materials. However some questions remain, especially around the observations made from flow experiments. Is there still a possibility that solid helium is super solid ?

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