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Quantum plasticity of helium crystals
The plasticity of solids is usually attributed to the motion of their
dislocations. Solid helium offers unique opportunities to study the
basic principles of plasticity. This is because it can be prepared at
low temperature without any impurity and with very low dislocation
densities. We will show video sequences to explain how we measure the
elastic properties of helium crystals as a function of their
orientation. Taking advantage of these exceptional properties, we have
discovered that, in the absence of impurities, helium crystals do not
resist to shear in particular directions. Our series of measurements
demonstrate that this exceptional softening is due to dislocations
gliding by quantum tunneling along the basal planes of the hexagonal
structure. This ``quantum plasticity’’ disappears as soon as traces of
3He impurities bind to dislocations and apparently suppress their
mobility. I will explain why this plasticity is an alternative
explanation for the proposed ``supersolidity’’ of the same crystals at
the same temperature.
(*) in collaboration with A. Haziot, X. Rojas, A. Fefferman and
J. Beamish
Séminaires Gulliver : consulter le programme
Informations contextuelles :
Contact : michael.schindler@espci.fr