New Evidence for a Superfluid Solid

In January 2004, two physicists at Penn State presented the results of an experiment in which at very low temperatures one solid (solidified helium-4) passed through another solid (a glasslike material called vycor) without any friction (Update 669). Now, the same researchers, Moses Chan (chan@phys.psu.edu) and Eun-Seong Kim, have modified their approach to demonstrate "superflow," the superfluid-like behavior of a solid, in a new way. This time, the solidified helium is not ensconced in any glass matrix. The He atoms are admitted to an open ring-shaped channel in a simple chamber which is free to swivel. Next the He are chilled and submitted to high pressure, causing solidification. One can tell that the helium at this point is solid and not liquid because of the characteristic oscillation (swiveling) properties. At an even lower temperature, 230 mK, the swiveling changes again, suggesting to Chan and Kim that a portion of the solid (about 1.5% of the sample) has metamorphosed into a freely flowing---but still solid---state of matter, or a frictionless "supersolid." (Science Express, 3 September.)