Observation of metastable hcp solid helium
Laboratoire Kastler Brossel, École Normale Supérieure, Université Pierre et Marie Curie, CNRS 24 rue Lhomond, 75005 Paris, France, EU
Accepted: 3 August 2011
We have produced and observed metastable solid helium-4 below its melting pressure between 1.1 K and 1.4 K. This is achieved by an intense pressure wave carefully focused inside a crystal of known orientation. An accurate density map of the focal zone is provided by an optical interferometric technique. Depending on the sample, minimum density achieved at focus corresponds to pressures between 2 and 4 bar below the static melting pressure. Beyond, the crystal undergoes an unexpected instability much earlier than the predicted spinodal limit. This opens a novel opportunity to study this quantum crystal in an expanded metastable state and its stability limits.
PACS: 67.80.-s – Quantum solids / 64.60.My – Metastable phases / 67.25.dt – Sound and excitations
© EPLA, 2011