This is very good. Essentially two electrons lock together
preventing reaction with the surrounding atoms and producing super
conductance. This appears general enough
to apply across the field and to other characteristics. It really works well and is surprisingly
simple.
It also supplies design
direction and that should translate quickly into superiors products and plenty
of fabrications whose affinity was never suspected.
It has never been
enough to achieve a higher temperature if it could not be used. That way now ends and maybe we can even use
it in graphene.
New theory may
revolutionize superconductors
By
Bill Steele Dec. 5, 2013
"Nanostripes"
of alternating electrons and holes (spaces where electrons should be that
appear as positive charges) appear in this scanning tunneling microscope image
of a copper-oxide superconductor, just one of many odd patterns seen in years
of observations of high-temperature superconductors.
An
"antiferromagnetic" state, where the magnetic moments of electrons
are opposed, can lead to a variety of unexpected arrangements of electrons in a
high-temperature superconductor, then finally to the formation of "Cooper
pairs" that conduct without resistance, according to a new theory.
High-temperature
superconductors exhibit a frustratingly varied catalog of odd behavior, such as
electrons that arrange themselves into stripes or refuse to arrange themselves
symmetrically around atoms. Now two physicists propose that such behaviors –
and superconductivity itself – can all be traced to a single starting point,
and they explain why there are so many variations.
This
theory might be a step toward new, higher-temperature superconductors that
would revolutionize electrical engineering with more efficient motors and
generators and lossless power transmission.
J.C.
Séamus Davis, the James Gilbert White Distinguished Professor in the Physical
Sciences at Cornell and director of the Center for Emergent Superconductivity
at Brookhaven National Laboratory, and Dung-Hai Lee, professor of physics at
the University of California-Berkeley and faculty scientist at Lawrence
Berkeley National Laboratory, describe their theory in the Oct. 7 issue of the
Proceedings of the National Academy of Sciences.
The
oddities, known as intertwined ordered phases, seem to interfere with
superconductivity. “We now have a simple way to understand how they are created
and hopefully this understanding will help us to know how to get rid of them,”
said Lee.
Superconductivity,
where current flows with zero resistance, was first discovered in metals cooled
almost to absolute zero. Recently, complex crystals of copper, iron and some
other metals combined with trace elements have been found to superconduct at temperatures
up to around 150 Kelvins (degrees Celsius above absolute zero). For the last 10
years, Davis has examined these materials with scanning tunneling microscopes
so well insulated from vibration that they can scan a surface in steps smaller
than the width of an atom, while measuring the energies of electrons under
their probes. He has discovered several of the intertwined phases of
high-temperature superconductors, which appear in scans as unexpected
arrangements of the electronic structure, and found them to vary widely from
one material to another.
“[Our
work] was not random; we were trying to map out all the known phenomena,” Davis
said.
Most
subatomic particles have a tiny magnetic field – a property physicists call
“spin” – and electrical resistance happens when the fields of electrons
carrying current interact with those of surrounding atoms. Two electrons can join like two bar magnets, the north pole of one
clamping to the south pole of the other, and this “Cooper pair” is magnetically
neutral and can move without resistance. Lee and Davis propose that this
“antiferromagnetic” interaction is the universal cause not only for
superconductivity but also for all the observed intertwined ordering. They
show how their “unified” theory can predict the phenomena observed in
copper-based, iron-based and so-called “heavy fermion” materials.
But
if the cause is always the same, why do different materials exhibit different
oddities? The difference, they say, is in the varying energy levels of the
electrons that are free to carry current, which can be described by a
mathematical structure called the ”Fermi surface.”
The
new high-temperature superconductors are derived from orderly crystals where
the same arrangement of atoms is repeated over and over and the spins of
electrons alternate up and down from one unit cell to another. Although this
favors antiferromagnetic interaction, electrons are not free to form Cooper
pairs. Doping with trace elements distorts the crystal structure and removes
some electrons, changing the Fermi surface. Whether Cooper pairing or some
other ordering will take place depends on the shape of the Fermi surface, the
researchers said.
Heat
makes atoms move and can shake Cooper pairs apart, so the holy grail is to
design a material where the pairs are bound together so strongly that
superconductivity can happen even up to room temperature. It might be possible
to describe a Fermi surface that would create that condition, and perhaps then
imagine what crystal structure it would require. “Ideally we would like to
be able to tell the materials scientist to put elements X, Y and Z
together,” Lee said. “Unfortunately we can’t do that yet.”
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