Tests for BEC and/or Superfluid Behavior in Solid 4He

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*****NON-TECHNICAL ABSTRACT*******Condensed matter, at low temperatures, displays properties that contradict our intuition. The most peculiar of these are superconductivity and superfluidity. The former means that some metals can conduct electricity without loss of energy below a certain temperature (its critical temperature). The latter means that liquid helium below its critical temperature has zero viscosity and flows without loss of energy. For example, if a superfluid in a bucket is rotating with the bucket, when the bucket is stopped, the superfluid will continue to rotate without slowing down, as long as it is maintained at low enough temperature to remain a superfluid. Another peculiar property that has been predicted is that solid helium could also exhibit superfluidity even though it is a solid. Although predicted, it is only recently that researchers have possibly observed this property of solid helium. It is not yet certain whether the observed behavior is the anticipated "supersolid" however a new, previously unknown, state of matter has been discovered. This award will support a project with the objective identifying the nature of this new state. The researchers at the University of California, San Diego and colleagues at Johns Hopkins University will investigate this new state of matter using a wide variety of experimental techniques. Along exploring the new state of matter, this project will provide training for a graduate student, a post doc, and undergraduates. ****** TECHNICAL ABSTRACT*******Solid helium is a unique material in that the atoms are very weakly bound and have small mass. Due to unusually large overlap of the wave functions of the atoms, the material may exhibit unusual quantum properties. The most dramatic possibility is that the solid will exhibit at the same time both crystalline order of the atoms and a Bose-Einstein condensation and/or superfluid behavior. Recent experimental results have found evidence of a new state of matter in solid He at very low temperatures. Whether this new state is the theoretically predicted "supersolid" state is still under investigation. This award will support researchers at the University of California, San Diego and colleagues at Johns Hopkins University in their attempt to determine the nature of this new state. A variety of experiments including neutron scattering, thermodynamic measurements, and acoustic/ultrasonic measurements will be used to explore and identify this state of matter. The work will bring a graduate student, a post doc and undergraduates into the discovery of a new state of matter that will contribute importantly to our understanding of condensed matter.