These three false-color images, from left, depict the density of cesium atoms in a superfluid (conducting) state, in a transition state and finally in an insulating state. The original sample consisted of a single-layer of cesium atoms that formed a sheet measuring 80 microns in diameter, barely visible to the naked eye. Green indicates the lowest density of atoms. Red indicates a high, constant density. Physicists call this a plateau, which a team of scientists have observed for the first time. (Courtesy: Nathan Gemelke and Cheng Chin/University of Chicago)

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These three false-color images, from left, depict the density of cesium atoms in a superfluid (conducting) state, in a transition state and finally in an insulating state. The original sample consisted of a single-layer of cesium atoms that formed a sheet measuring 80 microns in diameter, barely visible to the naked eye. Green indicates the lowest density of atoms. Red indicates a high, constant density. Physicists call this a plateau, which a team of scientists have observed for the first time. (Courtesy: Nathan Gemelke and Cheng Chin/University of Chicago)

U. CHICAGO (US)—Physicists have, for the first time, directly observed a group of atoms transform from a conducting state into an insulating state, the initial step toward simulating the dynamics of electrons in a solid.

“It opens up much richer phenomena to explore,” says Cheng Chin, an assistant professor in physics at the University of Chicago.  “How you can make the transition from a conducting material to a nonconducting material is difficult to conceive.” But using super-cooled atoms to simulate the behavior of electrons, Chin’s team was successful in doing so.

“It’s nearly impossible to resolve the dynamics of electrons,” Chin explains, because they move from atom to atom in trillionths of a second. The Chicago physicists dodged this problem by cooling a single layer of cesium atoms to temperatures near absolute zero (minus 459.67 degrees Fahrenheit). Then they magnetically controlled the motion of the atoms on a millisecond time scale (thousands of a second). Despite being a billion times slower than electrons actually move, the physics remains the same.

“We made a thin film of atoms, and then we watched how they distributed themselves inside our chamber,” Chin says.

What they observed confirmed a prediction that another team of scientists made in 2000: While the atoms are in a superfluid state (conducting), they experience very little repulsive force between each other. When moving freely, these atoms can become compressed with the application of pressure.

“There’s a certain mobility when you apply a force. You can easily compress a conducting sample,” Chin explains.

But when a magnetic field, which initiated a much greater repulsive force between the atoms, was applied, they became jammed and could not be deformed. The atoms had entered an incompressible insulating state.

The research appears in the Aug. 20 issue of Nature and was funded by the National Science Foundation, the Defense Advanced Research Profits Agency, and the Grainger Foundation.

University of Chicago news: www-news.uchicago.edu