Superfluids are capable of overflowing containers without having more material added to them, even constantly flowing out of a basin, like a waterfall. These substances are able to flow, with no friction, up to a certain velocity, known as the "superfluid critical velocity." They can also leak through solid glass, making them some of the strangest materials known to physics.
In 1937, physicists discovered that Helium-4 can be turned into a superfluid when it reaches extremely cold temperatures.
Lev Landau, a noted Soviet physicist, predicted in 1941 that super-cooled helium would exhibit a form of excitation, similar to that caused by particles, which researchers labeled a roton. That set off years of debate between physicists, including noted scientist Richard Feynman, concerning the nature of rotons.
"Even nowadays, after seven decades, it remains an issue of interest and controversy," Cheng Chin, physics professor at the University of Chicago, said.
Atomic superfluids offer researchers an opportunity to test superconductors, which could lead to a wide variety of applications in the outside world.
At present, between 30 and 40 percent of electricity is lost during transmission between power plants and homes. However, the adoption of superconductors in electrical grids is currently impractical, due to the high cost of such materials and the fact they need to be cooled to such low temperatures.
Now, researchers at the university have created an atomic superfluid from cesium-133 capable of creating the roton structure. The team has also developed a new method of detecting roton behavior, which should make detection of the process easier than ever before.
Cesium-133 was placed in a cylindrical container, roughly 12 inches high, and the material was cooled down to just a tiny fraction of a degree above absolute zero. Infrared laser beams were used to trap 30,000 atoms in a tiny volume, which was then subject to vibrations, in a process dubbed the shaken lattice technique. It is during this shaking that the roton effect can be measured. While this is happening, researchers carefully measure the way superfluids are altered by the roton properties of the material. The technique was first devised as a means of testing magnetic features of supercool materials.
The superfluid only displays roton features for a few seconds before the property disappears.
Washington State University researchers, as well as Chinese physicists, developed other methods of creating roton effects in super-cooled materials, soon after the discovery in Chicago.
"Our experiments provide a new platform to study excitations of a superfluid. They can help us better identify the key issues that limit the robustness of superconductivity," Chin said.
Analysis of roton effects in superfluids was published in the journal Physical Review Letters.
