Fermi gas is superfluid

First measurement of the flow properties of an exotic matter state

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Scientists have for the first time measured the flow properties of an exotic matter state, a so-called Fermi gas. The result published in "Science" not only shows that such a Fermi gas moves without any internal frictional resistance and is thus supra-fluid. They also confirm that it can serve as a model for the state of the interior of neutron stars or matter microseconds after the Big Bang.

Fermions are elementary particles with a half-integer spin. In addition to electrons and quarks, they also include composite particles that consist of an odd number of quarks, such as protons or neutrons, but also certain atomic isotopes such as lithium-6. At extremely low temperatures near absolute zero, these fermions enter a state where they no longer interact with each other, forming a so-called Fermi gas.

For the first time, scientists have succeeded in measuring the viscosity of this exotic state of matter in the laboratory. The American research team led by John Thomas of Duke University used an atomic gas of lithium-6 atoms, which was cooled in a tiny cage of laser light to a few billionths of a degree above absolute zero. Placed in a strong magnetic field, a Fermi gas was created.

Vibrating gas without friction

To measure the flow properties of this gas, the researchers now began to open the trap, in which the Fermi gas was trapped, in rapid succession, then close it again. This caused the radius of the gas to vibrate. The speed of the oscillations allowed conclusions about the viscosity of this matter state. It turned out that the Fermi gas deformed with almost no internal friction, behaving like a suprafluid fluid.

"These results are extremely important for solid state physics and especially for high temperature superconductivity research, " commented Kathy Levin, a theoretical physicist at the University of Chicago. display

Model for neutron stars and big bang

However, Fermi gas is also considered to be an important model for exotic matter forms found inside neutron stars, possibly in the first few microseconds after the Big Bang. For from the universal properties of this gas, such as the atomic distance of the lithium-6 atoms, researchers can extrapolate on the neutron distance of matter in the neutron star and deduce it from more advanced properties. These values, in turn, can be compared to the predictions of the models and theories.

(Duke University, Dec 14, 2010 - NPO)