title: Anomalous softening of ⁴He crystals.
abstract: We have measured the elasticity of high quality ultrapure ⁴He single crystals in the low temperature region where supersolidity is supposed to occur. At 20 mK, our results are consistent with elastic coefficients previously measured at 1.2 K. As the temperature increases from 20 to 100 mK, a large softening occurs because dislocations unpin from ³He impurities. In the absence of ³He impurities, dislocations are free to move down to 20 mK; the crystals are soft. The large magnitude of this anomalous softening shows that dislocations form a mobile mosaic structure. It illustrates the remarkable quantum plasticity of ⁴He crystals.
authors.affiliation: Laboratoire de Physique Statistique de l'Ecole Normale Supérieure, associé au CNRS et aux Universités Denis Diderot et P.M Curie, 24 rue Lhomond 75231 Paris Cedex 05, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Rojas
authors.forename: Ariel
authors.initials: A
authors.lastname: Haziot
authors.forename: Victor
authors.initials: V
authors.lastname: Bapst
authors.forename: Sébastien
authors.initials: S
authors.lastname: Balibar
authors.forename: Humphrey J
authors.initials: HJ
authors.lastname: Maris