test_moissonnage_selune
type: Agent

Dislocation motion in solid Helium-4
type: Distribution
access URL: https://theses.hal.science/tel-00856731
format: HTML
issued: 2026-05-09T18:18:17.787755
modified: 2026-05-09T18:18:17.770395

Dislocation motion in solid Helium-4
type: Dataset
contact point: Organization
  fn: CCSD
keyword: physcondcm-msphysics-physicscondensed-matter-cond-matmaterials-science-cond-matmtrl-sci
keyword: plasticite
keyword: solid-helium
keyword: acoustic
keyword: dislocation
keyword: theses
keyword: helium-solide
keyword: infoeu-reposemanticsdoctoralthesis
keyword: plasticity
keyword: acoustique
landing page: https://theses.hal.science/tel-00856731
description: We have shown that the shear modulus of Helium-4 single crystals is highly reduced in one particular direction if their dislocations are free to move. This "Giant Plasticity'' occurs at low enough temperature where thermal phonons disappear and probably down to absolute zero if Helium-3 impurities are suppressed. By studying single crystals with various orientations, we have identified the gliding plane of the dislocations: it is the basal plane of the hcp structure. We found no dissipation in the giant plasticity region and a linear elastic behaviour for single crystals down to 10 mK and nanobar stresses. This suggests that dislocations are strings moving freely with no measurable Peierls barriers to overcome, as assumed in the Granato-Lücke theory. We have also demonstrated that the dissipation occurring at higher temperature is due to collisions with thermal phonons. It allowed us to measure precisely the dislocation densities (10^4 to 10^6 cm^-2 depending on crystal quality) and lengths (50 to 200 microns) and to show that these dislocations are grouped in sub-boundaries, consequently poorly connected. These results rule out most existing scenarios for a possible supersolidity of solid Helium-4. A last series of experiments gave us the evidence for a critical dislocation speed under which the impurities bound to the dislocations can follow their motion. A comparison with classical crystals is interesting.
issued: 2026-05-09T18:18:17.785376
language: fr
modified: 2026-05-09T18:18:17.785382