title: Search for Dislocation Free Helium 4 Crystals.
abstract: The giant plasticity of [Formula: see text]He crystals has been explained as a consequence of the large mobility of their dislocations. Thus, the mechanical properties of dislocation free crystals should be quite different from those of usual ones. In 1996-1998, Ruutu et al. published crystal growth studies showing that, in their helium 4 crystals, the density of screw dislocations along the c-axis was less than 100 per cm[Formula: see text], sometimes zero. We have grown helium 4 crystals using similar growth speeds and temperatures, and extracted their dislocation density from their mechanical properties. We found dislocation densities that are in the range of 10[Formula: see text]-10[Formula: see text] per cm[Formula: see text], that is several orders of magnitude larger than Ruutu et al. Our tentative interpretation of this apparent contradiction is that the two types of measurements are somewhat indirect and concern different types of dislocations. As for the dislocation nucleation mechanism, it remains to be understood.
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France.
authors.forename: F
authors.initials: F
authors.lastname: Souris
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France ; CNRS Institut NÉEL, Université Grenoble Alpes, BP 166, 38042 Grenoble Cedex 9, France.
authors.forename: A D
authors.initials: AD
authors.lastname: Fefferman
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France ; Department of Physics, Pennsylvania State University, University Park, PA 16802 USA.
authors.forename: A
authors.initials: A
authors.lastname: Haziot
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France.
authors.forename: N
authors.initials: N
authors.lastname: Garroum
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France ; Department of Physics, University of Alberta, Edmonton, AB T6G 2E1 Canada.
authors.forename: J R
authors.initials: JR
authors.lastname: Beamish
authors.affiliation: Laboratoire de Physique Statistique de l'École Normale Supérieure associé au CNRS et aux Universités P.M. Curie et D. Diderot, 24 rue Lhomond, 75231 Paris Cedex 05, France.
authors.forename: S
authors.initials: S
authors.lastname: Balibar
keywords: Dislocations; Plasticity; Solid helium