*Harvard* *Condensed Matter Theory Seminars*

**Superfluid disorder in quantum solids**

- I will briefly review old ideas on how can superfluidity occur
in a crystalline solid, and discuss 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. Finally, I will discuss the "ultimate"
superfluid disordered state---a helium superglass which we observed to
be remarkably stable at low temperatures and elevated pressures.

Harvard Physics Calendar | | Harvard Condensed Matter Theory