Studies of the Supersolid State of Matter

****NON-TECHNICAL ABSTRACT****

An important theme in physics is the study macroscopic quantum phenomena, or understanding the effect quantum mechanics on a collection of atoms or molecules of macroscopic dimensions. A familiar macroscopic quantum phenomenon is superconductivity where electricity can flow in some metals and oxides with absolutely no resistance below some specific temperature called the transition temperature. A related phenomenon is superfluidity where liquid helium, when cooled below 2K or 2 degrees above absolute zero, can flow forever when it is set in motion. During the previous funding cycle a remarkable discovery was made; such a superflow also occurs in solid helium below 0.2K. While the experiments have been replicated by other groups, this supersolid behavior is not yet understood. A number of theoretical papers suggest the supersolid phenomenon is a consequence of imperfections in the helium crystal. This individual investigator project will support an effort to grow and characterize the highest quality helium crystals and to look for supersolid behavior in them. If successful this project will lead to a better understanding of the phenomenon. Graduate students involved in this research will receive rigorous training in experimental physics and will be well prepared for careers in academia and industries. They will also participate in a range of K-12 outreach activities spearheaded by the P.I..

**** TECHNICAL ABSTRACT****

This individual investigator award supports experimental investigations on the nature of superfluidity in solid helium, which was discovered in a series of torsional oscillator experiments during the prior funding period. This behavior has been replicated by other laboratories, however many questions concerning the phenomenon of supersolidity remain. The crystal quality of the solid samples studied to date has not been well characterized and a number of theoretical papers suggest the observed supersolid behavior is a consequence of defects, dislocations and grain boundaries in the crystals. High quality helium crystals will be grown and investigated using ultrasound resonance, x-ray, and thermodynamic (heat capacity) techniques in an effort to further our understanding of the supersolid behavior. Graduate students involved in this research will receive rigorous training in cryogenics and precision measurements techniques and thus will be well prepared for future careers in academia and industries. They will also participate in a range of K-12 outreach activities spearheaded by the P.I..