“It opens up much richer phenomena to explore,” said Cheng Chin, an assistant professor in physics at the University. Chin’s team conducted the experiment as the first step in a project to simulate the dynamics of electrons in a solid.
“How you can make the transition from a conducting material to a non-conducting material is difficult to conceive,” said Chin. But his team actually observed such a transition using super-cooled atoms to simulate the behavior of electrons.
“It’s nearly impossible to resolve the dynamics of electrons,” Chin said, 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). This is a billion times slower than electrons move, but the physics remains the same.
“We made a thin film of atoms, and then we watched how they distributed themselves inside our chamber.”
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 said.
But when the Chicago researchers applied a magnetic field, initiating a much greater repulsive force between the atoms, they became jammed and could not be deformed. The atoms had entered an incompressible insulating state.
Citation: Gemelke, Nathan; Zhang, Xibo; Hung, Chen-Lung; and Chin, Cheng, “In-situ Observation of Incompressible Mott-Insulating Domains of Ultracold Atomic Gases,” Nature, Aug. 20, 2009.
Funding sources: National Science Foundation, Defense Advanced Research Projects Agency, and the Grainger Foundation.
Steve Koppes | Newswise Science News
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