Date/Time
Date(s) - 16/01/2008
3:20 pm - 4:20 pm

Title: Supersolid Phase of Helium-four: A Theoretical Study

Speaker: Dr. Massimo Boninsegni

Institute: University of Alberta

Location: ABB 102

Description:

The observation of a non-classical moment of inertia in solid Helium-four by Kim and Chan (Science 305, 1941 (2004)) has provided the first experimental evidence of a possible supersolid phase of matter, namely a crystalline phase capable of sustaining dissipationless flow. However, the interpretation of the experimental findings in terms of supersolidity of the crystal phase remains controversial at the theoretical level. Using quantum Monte Carlo methods, based on a recently developed new scheme know as “Worm Algorithm”, we have investigated Bose condensation in a perfect crystal, as well as the leading theoretical scenarios of supersolidity, namely that in which superflow occurs in a highly dilute gas of vacancies. We find that a perfect crystal is not supersolid, and that single vacancies and interstitials have large activation energies, and that vacancies in a helium-four crystal phase separate instead of forming a homogeneous gas. Motivated by recent experiments by Sasaki et al. (Science 313, 1098 (2006)), we also explored superflow of Helium at grain boundaries. Finally, numerical evidence of a quasi-one-dimensional supersolid in the presence of a screw dislocation is discussed.