NIST/University of Colorado Scientists create new form of matter: A fermionic condensate

01/27/04

A related press conference release can be seen here



False color images of a condensate formed from pairs of fermion potassium atoms. Higher areas indicate a greater density of atoms.
Images from left to right correspond to the increasing strength of attraction between the atoms that form fermion pairs as the magnetic field strength is varied.

Scientists at JILA, a joint laboratory of the Department of Commerce's National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder (CU-Boulder) report the first observation of a "fermionic condensate" formed from pairs of atoms in a gas, a long-sought, novel form of matter. Physicists hope that further research with such condensates eventually will help unlock the mysteries of high-temperature superconductivity, a phenomenon with the potential to improve energy efficiency dramatically across a broad range of applications.

The research is described in a paper to be published in the Jan. 24-30 online edition of Physical Review Letters by JILA authors Deborah S. Jin, a physicist at NIST and an adjoint associate professor at CU-Boulder, and Markus Greiner and Cindy Regal, a post-doctoral researcher and graduate student at CU-Boulder. (Expected publication date is Jan. 28, 2004.)

"The strength of pairing in our fermionic condensate, adjusted for mass and density," Jin explains, "would correspond to a room temperature superconductor. This makes me optimistic that the fundamental physics we learn through fermionic condensates will eventually help others design more practical superconducting materials."

The new work complements a previous major achievement, creation of a "Bose-Einstein" condensate, which earned JILA scientists Eric Cornell and Carl Wieman, the Nobel Prize in Physics in 2001. Bose-Einstein condensates are collections of thousands of ultracold particles occupying a single quantum state, that is, all the atoms are behaving identically like a single, huge superatom. Bose-Einstein condensates are made with bosons, a class of particles that are inherently gregarious; they'd rather adopt their neighbor's motion than go it alone.

Unlike bosons, fermions--the other half of the particle family tree and the basic building blocks of matter--are inherently loners. By definition, no fermion can be in exactly the same state as another fermion. Consequently, to a physicist even the term--fermionic condensate--is almost an oxymoron.

For many decades, physicists have proposed that superconductivity (which involves fermions) and Bose-Einstein condensates (BEC) are closely linked. Theorists have hypothesized that superconductivity and BEC are two extremes of superfluid behavior, an unusual state where matter shows no resistance to flow. Superfluid liquid helium, for example, when poured into the center of an open container, will spontaneously flow up and over the sides of the container.

In the current experiment, a gas of 500,000 potassium atoms was cooled to temperatures below 50 billionths of a degree Celsius above absolute zero (minus 459 degrees Fahrenheit) and then a magnetic field was applied near a special "resonance" strength. This magnetic field coaxed the fermion atoms to match up into pairs, akin to the pairs of electrons that produce superconductivity, the phenomenon in which electricity flows with no resistance. The Jin group detected this pairing and the formation of a fermionic condensate for the first time on Dec. 16, 2003.

The temperature at which metals or alloys become superconductors depends on the strength of the "pairing" interaction between their electrons. The highest known temperature at which superconductivity occurs in any material is about minus 135 degrees Celsius (minus 216 degrees Fahrenheit).

Source: Eurekalert & others

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