Physics (Internal)

Superfluid disorder in quantum solids

This event is part of the Biophysics/Condensed Matter Seminar Series.

I will briefly review old ideas on how can superfluidity occur in a crystalline solid, briefly mention a theorem that any supersolid in continuous space must be in the incommensurate state and have gapless vacancies and/or interstitials. In He-4 vacanices and interstitials are gapped, and thus ideal crystals are insulating. I will present path-integral Monte Carlo data to prove that. To explain recent experiments on the non-classical moment of inertia of He-4 solids one has to consider various types of disorder. I will show examples of superfluid defects in lattice and helium systems, and discuss which of them are likely to be present in experimental samples. For one thing, grain boundaries in hcp helium are generically superfluid at low T! Finally, I will discuss the “ultimate” disordered superfluid state—a helium superglass which we observed to be remarkably stable at low temperatures and elevated pressures.