Is solid helium superfluid?

by David M. Ceperley (Department of Physics, University of Illinois at Urbana-Champaign)

Tuesday 28 Jun 2011, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Edificio G. Marconi)

Andreev, Lifshitz, Chester, and Leggett suggested in 1970 that a quantum crystal such as bulk helium-4 under pressure might simultaneously show solid and superfluid behavior. Experiments by Kim and Chan starting in 2005 found indications for such a supersolid phase. The theoretical explanation of superflow in a crystal assumed vacancies, however, neither experiments or computer simulations find them. Microscopic calculations (specifically Path Integral Monte Carlo) do not show a superfluid response, but they are limited to equilibrium samples of small crystals, implying there is a discrepancy between the best computer simulations and the "supersolid" interpretation of experiments. More recent experiments and theory lead to the view that defects such as grain boundaries, dislocations or impurities are responsible for the observations.