
How electrons 'gain weight'
Date: Thursday, November 01, 2007 @ 22:40:42 UTC Topic:
Rutgers physicists show how electrons 'gain weight' in metal compounds near absolute zero
Rutgers University physicists have performed computer simulations that
show how electrons become one thousand times more massive in certain
metal compounds when cooled to temperatures near absolute zero – the
point where all motion ceases. The models may provide new clues as to
how superconductivity works and how new superconducting materials could
be fabricated.
In a paper posted to Science Express, a Web site of research reports slated for upcoming print editions of Science,
the researchers describe how electrons interact with other particles in
these compounds to morph into what physicists call a fluid of “heavy
quasiparticles” or a “heavy fermion fluid.” While this effect has been
previously observed in some materials, the Rutgers work employs new
materials to provide a level of detail that has eluded scientists so
far.
“In this paper, we essentially track the fate of electrons as we
lower the temperature,” said Gabi Kotliar, Board of Governors Professor
of Physics in the School of Arts and Sciences. “Experimental physicists
may have seen different aspects of this behavior, or they may have seen
behaviors they did not understand. Our calculations reconcile what
they’ve seen.”
The Rutgers researchers based their models on experiments using a
new metallic crystalline compound made of the elements cerium, indium
and iridium. This and similar compounds that substitute cobalt and
rhodium for iridium are excellent test beds for observing heavy
electron behavior.
Earlier investigations used high-temperature superconducting
materials called cuprates, which failed to give physicists a clear view
of electron behavior because of disorders in the crystalline structure
caused by doping. The new cerium-based compounds are simpler to study
because they are free of dopants.
“The new compounds are for us what fruit flies are for genetics
researchers,” said Kristjan Haule, assistant professor of physics and
astronomy. “Fruit flies are easy to breed and have a simple gene makeup
that’s easy to change. Likewise, these compounds are easy to make,
structurally straightforward and adjustable, giving us a clearer view
into the many properties of matter that arise at low temperatures. For
example, we can use a magnetic field to kill superconductivity and
examine the state of matter from which superconductivity arose.”
These compounds are examples of strongly
correlated materials, or materials with strongly interacting electrons,
that can’t be described by theories that treat electrons as largely
independent entities. The terms “heavy quasiparticles” refers to how
electrons interact with each other and, as a result of those
interactions, form a new type of particle called a “quasiparticle.”
In explaining how this effect appears at low temperatures and
vanishes at higher ones, Haule noted that electrons in f-orbitals are
tightly bound to cerium atoms at room temperature. But as the
temperature drops, the electrons exhibit coherent behavior, or
delocalization from their atoms. At 50 degrees above absolute zero, or
50 degrees Kelvin, the researchers clearly observe quasiparticles as
electrons interact with each other and other electrons in the metal
known as conduction electrons.
Source: Rutgers University Via: http://www.physorg.com/news113146663.html
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