Ven. 27/04/2018 10:00 Grande Ourse, Bâtiment 13, Etage 1
GRUCKER Jules (Laboratoire Kastler Brossel, Sorbonne Université, CNRS, ENS, Collège de France)
The metastable states of solid and liquid He-4
Condensed He-4 is a fascinating system because it exhibits quantum properties at the macroscopic scale. The most famous of these is probably the transition of the liquid into a so called superfluid state when cooled down below 2.17 K at vapor pressure. I will present and discuss experiments investigating the metastable phases of liquid and solid He-4. Metastable solid He-4 is interesting because it is a potential candidate for a hypothetical (not yet discovered) supersolid state of matter. Metastable liquid He-4 is interesting because due to its extreme purity, it is a model system to study homogeneous cavitation. The metastable states are produced by focusing an acoustic wave in the bulk of the solid (liquid). We measure the local density within the wave thanks to an optical time-resolved interferometric method. In both metastable liquid and solid He-4, we have observed instabilities at densities which are not compatible with theoretical predictions. In the particular case of metastable liquid He-4, our density measurement of its cavitation threshold especially questions the validity of a well theoretically established equation of state of the metastable liquid. It then appears necessary to try to measure the equation of state experimentally which could be done using a stimulated Brillouin scattering technique.
Pour plus d'informations, merci de contacter Berthier L.