Physicists at Rutgers and Columbia universities have gained new insight into the origins of superconductivity – a property of metals where electrical resistance vanishes – by studying exotic chemical compounds that contain neptunium and plutonium.
While superconductivity holds promise for massive energy savings in power transmission, and for novel uses such as levitating trains, today it occurs only at extremely cold temperatures. As a result, its use is now limited to specialized medical and scientific instruments. Over the past two decades, scientists have made metals that turn superconducting at progressively higher temperatures, but even those have to be cooled below the temperature of liquid nitrogen.
Still, physicists believe room temperature superconductivity may be possible. The work reported by the Rutgers and Columbia physicists is a step in that direction – shedding new light on the connection between magnetism and superconductivity.
"The exotic compounds we're studying will not become practical superconducting materials; however, by studying them we can learn the trends that govern a material's transition to superconductivity" said Piers Coleman, physics professor at Rutgers.
Coleman, along with Rutgers graduate student Rebecca Flint and Columbia postdoctoral research scientist Maxim Dzero, are publishing their findings in an upcoming issue of the journal
Nature Physics. Their paper has been posted to the journal's advance publication web site at:
http://dx.doi.org/10.1038/nphys1024.
The compounds they've studied are made out of elements in the actinide series, including neptunium and plutonium. In these materials, active electrons are in "f-orbitals." In contrast, materials that make up today's highest-temperature superconductors, including copper or iron, have active electrons in "d-orbitals." The f-electron materials generally have lower superconducting temperatures than their d-electron counterparts; but they are easier to make and may be easier to understand.
"Electrons must bind together into pairs called 'Cooper pairs' for materials to become superconducting," Flint said. "In earlier studies, a small amount of magnetism was lethal to this pairing; however, in these materials, magnetism is not bad. It actually appears to play a central role in driving the pairing effect."
These new superconductors are part of a class of materials referred to as "heavy electron superconductors," metals that are filled with tiny, atomic-sized magnets known as "spins." When electrons pass through this forest of magnets, they slow down and move sluggishly as if they were extremely heavy.
"In most heavy electron superconductors, the electrons have to get heavy before they go superconducting," said Coleman. "But in the highest temperature versions, the electrons get heavy and become superconducting at the same time."
To understand this effect, the scientists have proposed a new type of electron pairing. "We've found that the electrons form much stronger pairs if they team up with one of the tiny atomic magnets – a combination that might be called a quantum-mechanical 'menage a trios,'" said Coleman. "The spin in the middle brings the pair of electrons close together, and a stronger pair means superconductivity at higher temperatures."
The scientists hope these ideas can be applied to d-electron materials, where the superconductivity may occur much closer to room temperature.
Source: Rutgers University
Related stories:
Researchers team up to probe iron-arsenic superconductors with new instrument
Researchers at the U.S. Department of Energy's Ames Laboratory are part of collaborative team that's used a brand new instrument at the DOE's Spallation Neutron Source to probe iron-arsenic compounds, the "hottest" new find in the race to explain and develop superconducting materials. Rob McQueeney, an Ames Laboratory physicist, was part of that team whose findings, published in the Oct. 10 issue (101) of
Physical Review Letters, mark the first research produced with the aid of the new tool.
Superconductivity can induce magnetism
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.
Magnetism and Superconductivity Observed to Exist in Harmony
(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.
Scientists reveal effects of quantum 'traffic jam' in high-temperature superconductors
(PhysOrg.com) -- Scientists at the U.S. Department of Energy's Brookhaven National Laboratory, in collaboration with colleagues at Cornell University, Tokyo University, the University of California, Berkeley, and the University of Colorado, have uncovered the first experimental evidence for why the transition temperature of high-temperature superconductors -- the temperature at which these materials carry electrical current with no resistance -- cannot simply be elevated by increasing the electrons' binding energy. The research -- to be published in the August 28, 2008, issue of
Nature -- demonstrates how, as electron-pair binding energy increases, the electrons' tendency to get caught in a quantum mechanical "traffic jam" overwhelms the interactions needed for the material to act as a superconductor -- a freely flowing fluid of electron pairs.
New theory for latest high-temperature superconductors
Physicists from Rice and Rutgers universities have published a new theory that explains some of the complex electronic and magnetic properties of iron "pnictides." In a series of startling discoveries this spring, pnictides were shown to superconduct at relatively high temperatures. The surprising discoveries created a great deal of excitement in the condensed matter physics community, which has been scrambling to better understand and document the unexpected results.
Scientists Shed Light on Heavy Electrons, Suggest New View of Superconductivity
(PhysOrg.com) -- Scientists from Los Alamos National Laboratory, the University of California, Irvine, and the University of California, Davis have proposed a new characterization for the bizarre behavior of certain super-cooled materials--many that act as superconductors--which suggests a paradigm shift in the way scientists understand superconductivity.
Room temperature superconductivity: One step closer to the Holy Grail of physics
Scientists at the University of Cambridge have for the first time identified a key component to unravelling the mystery of room temperature superconductivity, according to a paper published in today's edition of the scientific journal
Nature.
UBC physicists develop 'impossible' technique to study and develop superconductors
A team of University of British Columbia researchers has developed a technique that controls the number of electrons on the surface of high-temperature superconductors, a procedure considered impossible for the past two decades.