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Magnetism and Superconductivity Observed to Exist in Harmony
Posted on Thursday, August 28, 2008 @ 22:52:45 UTC by vlad
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(Physorg.com) -- Physicists at Los Alamos National Laboratory, along
with colleagues at institutions in Switzerland and Canada, have
observed, for the first time in a single exotic phase, a situation
where magnetism and superconductivity are necessary for each other's
existence.
Physicists have seen the battle
for supremacy between the competing states of magnetism and
superconductivity as one in which no truce could be struck. This
perplexing dilemma has thwarted scientists' quest for the
resistance-free flow of electrons, and, with it, the vast potential in
energy savings that superconductivity holds for ultra-efficient power
transmission, magnetic resonance imaging (MRI) technology, and other
applications.
In the current online advance edition of the journal Science,
the international team of scientists reports the simultaneous
observation of both states in a compound containing the elements
cerium, cobalt, and indium (CeCoIn5) at a temperature close
to absolute zero about 460 degrees below zero, Fahrenheit. Coauthor
Andrea Bianchi, who is now based at the University of Montreal, was the
first to see this phase at Los Alamos National Laboratory in 2003.
"This coexistence is an exotic superconducting state that has not
been observed in any other superconducting material," said Los Alamos
scientist Roman Movshovich, one of the paper's authors. "It shows a
very strong link between superconductivity and magnetism."
Scientists understand superconductivity as a phenomenon that occurs
when electrons spinning in one direction form pairs with electrons
spinning in the opposite direction, usually at very low temperatures.
These pairs, in turn, combine with each other to form a new
superconducting state of matter where electrons move resistance-free
through the material. Superconductivity is a manifestation of
interactions that take place between few particles (electrons and
atoms) that reveal themselves on a macroscopic scale, in samples that
we can see and touch. Magnetism, where electrons' magnetic spins are
fixed in space in an orderly fashion, requires participation of the
same electrons and therefore generally competes with superconductivity.
But why, in this particular case, magnetism and superconductivity
appeared at the same time in the same compound is still a mystery.
"It's not clear what the origin of this state is, or what creates or
modifies it," Movshovich said.
If physicists can work out how magnetism figures into the origin of
superconductivity, which is currently only possible at temperatures
hundreds of degrees below zero, they will be one step closer to the
"holy grail" of modern condensed matter physics: superconductivity at
temperatures high enough to eliminate expensive cooling liquids such as
nitrogen and helium.
"It's really a question of the chicken and the egg," said coauthor
Eric Bauer of Los Alamos. "Does superconductivity need magnetism in
this state, or does magnetism need superconductivity?"
The scientists applied a high magnetic field to a crystal of this
compound synthesized by Bauer and his colleague John Sarrao at Los
Alamos, suppressing its superconductivity. They found that, as a
consequence, the crystal also lost its magnetism. This evidence
suggests that without superconductivity, magnetism is not possible in
CeCoIn5. The converse, however, isn't necessarily true.
It appears that superconductivity could occur even in the absence
of magnetism, either at lower magnetic field, or at a slightly higher
temperature, Bauer said.
The extraordinary "cleanliness"
inherent in the quality of the crystal grown in the Materials Physics
and Applications division at Los Alamos was one of the reasons the team
was able to coax these coupled states from the compound, Movshovich
said. The importance of cleanliness was demonstrated in one of this
team's previous studies where minute amount of impurities were
introduced on purpose, and such samples did not display this fragile
superconducting/magnetic state.
With these "clean" crystals, a group led by Michel Kenzelmann of
the Paul Scherrer Institute and the Swiss Federal Institute of
Technology, both in Switzerland, probed the compound with a beam of
neutrons to elucidate its physical properties. Though neutrons don't
carry a charge like electrons and protons do, they still have a
magnetic spin that interacts with magnetic order inside a compound.
Based on the direction of the neutrons when scattered from the crystal,
the team was able to deduce the magnetic structure of the coupled
magnetic/superconducting state.
CeCoIn5 is what's known as a heavy fermion material because at low
temperatures its electrons act as if they are much heavier than they
really are, due to interactions with magnetic ions (Ce in this case) in
the lattice structure of the material. And although the experiments in
this latest round of research took place at low temperatures, electrons
in both heavy fermion compounds and high-temperature superconductors
are believed to pair up and move in much the same way, and the
fundamental knowledge obtained will contribute to our general
understanding of the superconducting phenomena. The team's findings are
likely to trigger further studies in similar compounds.
"This is a new paradigm for understanding the interplay between
magnetism and superconductivity," Bauer said. "It could help us find
the basis for understanding unconventional (high-temperature)
superconductivity."
Provided by Los Alamos National Laboratory
Via: http://www.physorg.com/news139159195.html
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Superconductivity can induce magnetism (Score: 1)
by vlad on Sunday, September 14, 2008 @ 17:10:55 UTC
(User Info | Send a Message) http://www.zpenergy.com | When an electrical current passes through a wire it emanates heat – a
principle that's found in toasters and incandescent light bulbs. Some
materials, at low temperatures, violate this law and carry current
without any heat loss. But this seemingly trivial property,
superconductivity, is now at the forefront of our understanding of
physics.
Full story: http://www.physorg.com/news140359809.html [www.physorg.com]
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Secrets behind high temperature superconductors revealed (Score: 1)
by vlad on Sunday, February 22, 2009 @ 21:55:31 UTC
(User Info | Send a Message) http://www.zpenergy.com | Scientists from Queen Mary, University of
London and the University of Fribourg (Switzerland) have found evidence
that magnetism is involved in the mechanism behind high temperature
superconductivity.
Writing in the journal Nature Materials,
Dr Alan Drew from Queen Mary's Department of Physics and his colleagues
at the University of Fribourg report on the investigation of a new high
temperature superconductor, the so-called oxypnictides. They found that
these exhibit some striking similarities with the previously known
copper-oxide high temperature superconductors - in both cases
superconductivity emerges from a magnetic state. Their results go some
way to explaining the mechanisms behind high temperature
superconductors.
Superconductors are materials that can conduct electricity with no
resistance, but only at low temperatures. High temperature
superconductors were first discovered in 1986 in copper-oxides, which
increased the operational temperature of superconductors by more than
100°C, to -130°C and opened up a wealth of applications. The complex
fundamental physics behind these high temperature superconductors has,
however, remained a mystery to scientists.
Dr Drew said "Last year, a new class of high-temperature
superconductor was discovered that has a completely different make-up
to the ones previously known - containing layers of Arsenic and Iron
instead of layers of Copper and Oxygen. Our hope is that by studying
them both together, we may be able to resolve the underlying physics
behind both types of superconductor and design new superconducting
materials, which may eventually lead to even higher temperature
superconductors."
Professor Bernhard, of the University of Fribourg, added: "Despite
the mysteries of high-temperature superconductivity, their applications
are wide-ranging. One exciting applications is using superconducting
wire to provide lossless power transmission from power stations to
cities. Superconducting wire can hold a much higher current density
than existing copper wire and is lossless and therefore energy saving."
An electrical current flowing round a loop of superconducting wire
can also continue indefinitely, producing some of the most powerful
electromagnets known to man. These magnets are used in MRI scanners, to
'float' the MagLev train, and to steer the proton beam of the Large
Hadron Collider (LHC) at CERN. Envisaged future applications of
superconductors exist also in ultrafast electronic devices and in
quantum computing.
Source: Queen Mary, University of London
Via: http://www.physorg.com/news154538523.html [www.physorg.com]
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