Squeezing superfluid from a stone: Coupling superfluidity and elasticity in a supersolid

John Toner
University of Oregon

Superfluidity - the ability of {\it liquid\/} $^4$He, when cooled below 2.176~K, to flow without resistance through narrow pores - is one of the most amazing phenomena in physics.

Supersolidity - the coexistence of superfluid behavior with the crystalline order of a solid---was proposed theoretically long ago as an even more exotic phase of {\it solid\/} $^4$He, but it has eluded detection until recently.

In 2004, Kim and Chan( E. Kim and M. H. W. Chan, Nature (London) {\bf 427}, 225 (2004); E. Kim and M. H. W. Chan, Science {\bf 305}, 1941 (2004).) reported the onset of ``nonclassical rotational inertia" in a torsional oscillator experiment with solid $^4$He, and they interpret their results as indicating the onset of supersolidity.

In this talk, I'll describe what a supersolid is, discuss the Chan et al experiments, and present the theory I've recently developed (with Paul Goldbart ofthe University of Illinois at Urbana-Champaign, and Alan Dorsey of the University of Florida) of the normal solid to supersolid (NS-SS) phase transition.

I'll also describe more recent work which incorporates dislocations into this theory, and which may explain many puzzling features of the Chan et al results, including the most puzzling one of all: why does the supersolid exist in the first place?