May 2012: Prof. John Reppy Casts More Doubt on Supersolid Helium
Can helium, when extremely cold, be both a frictionless superfluid and a crystalline solid at the same time? This material, called a supersolid has been theorized for decades. In spite of some experiments supporting supersolid helium from a team at Pennsylvania State University in 2004, Cornell professor of physics John Reppy has gathered experiemental evidence to refute those 2005 results by starting with the same experiment.
The initial experiment used a cylinder of a spongelike, porous glass called Vycor in a can atop a thin shaft. Reppy and undergraduate student Xiao Mi took also used a cell filled with Vycor but where previous experiments then began oscillating their sample at one frequency, Reppy and Mi compared signals at two frequencies to check for consistency.
Reppy’s observations showed that for solid helium at a given temperature, the two frequency shifts suggest that different amounts of helium have let go. That observation clashes with the supersolidity scenario, in which the fraction of the helium that flows should also depend on only the temperature.
This is not Prof. Reppy’s first challenge to supersolid helium, in a 2006 “Viewpoint” in the journal Physics, he questioned experimental results stating that “. . . what you’re seeing is a high-temperature phenomenon that disappears at low temperatures, rather than some new phenomenon that appears at low temperatures.”
To read about Prof. Reppy’s results in Science, click here.