Supersolid State of Matter

July 22 - 27, 2007
Stillwater, Minnesota

For nearly half a century the supersolid phase of matter has remained mysterious, not only eluding experimental observation, but also generating a great deal of controversy. The supersolid phase can be generally defined as one that combines typical crystalline properties, such as shear modulus and broken translation symmetry, with frictionless mass transport through the solid bulk. The striking, simultaneous presence of solid and superfluid properties in a single-component condensed matter system, results in a number of phenomena that defy our everyday experience.

Recent discovery by Kim and Chan of what is interpreted as a non-classical moment of inertia at low temperature in solid He-4 has elicited much excitement as a possible first observation of a supersolid phase. Several microscopic mechanisms have been suggested to underlie superfluidity in a perfect quantum crystal. However, as the initial experiment is being repeated by other groups, and concurrently different experiments and microscopic calculations are being carried out things turn out to be considerably more complicated (and thus more interesting) than expected. In the two years following the discovery more puzzles than answers have been provided to the fundamental issue of whether the supersolid phase exists, in helium or any other naturally occurring condensed matter system. Presently, there is no established theoretical framework to understand the body of experimental data, nor there is consistency between results obtained by different experimental groups. There are theoretical and experimental results which claim an insulating crystalline ground state and discuss instead disordered supersolid phases where superfluidity is induced by defects of the crystalline structure.

This workshop will bring together active researchers in the field, as well as several experts in related fields, to discuss the current status of the supersolid problem in helium, address existing controversies, both experimental and theoretical, and propose new strategies for their resolution. In a broader context, the workshop will look at the perspectives for finding supersolid phases in quantum lattice models, and understanding what interatomic potentials, given the freedom to design one, can support the supersolid phase in continuous space. We expect that the meeting will foster closer collaboration between the theoretical and experimental groups including the design of new experiments to test new ideas about the supersolid state and first-principles simulations of experimentally relevant samples.