Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

UA Physicist Discovers Exotic Superconductivity

17.08.2006
A University of Arizona physicist has discovered that powerful magnetic fields change the physical nature of superconductivity.

UA Associate Professor of Physics Andrei Lebed has discovered that strong magnetism changes the basic, intrinsic properties of electrons flowing through superconductors, establishing an "exotic" superconductivity.

"Understanding the physical nature of the electron pairs that define superconductors is one of the most important problems in condensed matter physics," Lebed said. He published the research earlier this year in Physical Review Letters. He said the work is one of his most important contributions to physics in his 20-year career.

A Dutch physicist, Heike Kamerlingh Onnes, is credited with discovering superconductivity in 1911, work for which he was awarded a 1913 Nobel Prize.

Kamerlingh Onnes' momentous discovery was that pure metals such as mercury, tin and lead become "superconductors" at very low temperatures. When cooled to near absolute zero temperatures, certain conducting metals suddenly lose all electrical resistance. At zero electrical resistance, the metals will conduct electric current endlessly.

Physicists began winning Nobel Prizes for pioneering theory to explain the phenomenon of superconductivity a half century ago. In 1957, American physicists John Bardeen, Leon Cooper and Robert Schrieffer proposed a comprehensive theory to explain the behavior of superconducting materials. The theory, called "BCS theory" for the scientists' surname initials, was the first great insight, the first big step in understanding superconductivity. The work garnered them the 1972 Nobel Prize in Physics.

Cooper had discovered that electrons in a superconductor don't act as individual particles, but as pairs, now called "Cooper pairs." When electrical voltage is applied to a superconductor, all Cooper pairs move as a single entity, establishing an electrical current. When the voltage is cut off, the current continues to flow indefinitely because there is no resistance to the Cooper pairs motion. This normally works only at very low temperatures. When the superconductor warms up, its Cooper pairs separate into individual electrons and the material becomes a normal non-superconductor.

"People always have thought about the Cooper pair as behaving as an elementary particle, which is characterized by size (or, roughly speaking, the average distance between the electrons in a Cooper pair), electric charge, spin, mirror reflection and time-reversal properties," Lebed said.

Contrary to this commonly held theory, Lebed said, "We show that superconducting electron pairs are not unchanged elementary particles but rather complex objects with characteristics that depend on the strength of a magnetic field."

QUANTUM MECHANICAL HURRICANES

Some background to understand how this works: American physicists David Lee, Douglas Osheroff, Robert Richardson and Anthony Leggett won Nobel Prizes in Physics in 1996 and 2003 for their theoretical and experimental studies of rotating Cooper pairs in helium-3. They discovered that electrons in a Cooper pair, no matter how far apart they are, have either conventional "singlet" or unconventional "triplet" internal rotation, or "spin" in quantum physics jargon.

When the spins of the two electrons are in opposite directions, one spinning up and the other spinning down, they are called singlets, or non-rotating Cooper pairs. When the spins are in same direction, they are called triplets, or rotating Cooper pairs.

Lebed has now discovered that super-strong magnetic fields create exotic Cooper pairs that behave according to the weird, non-intuitive laws of quantum mechanics: the electron pairs are both rotating and non-rotating at the same time. They behave kind of like microscopic "quantum mechanical hurricanes," as UA Regents' Professor Pierre Meystre, head of UA's physics department, put it.

MIRRORS LIKE ALICE'S OF WONDERLAND

Another unexpected and unique magnetic field-dependent property is mirror reflection.

Because Cooper pairs are quantum objects, they behave both as particles and as standing waves. One standing wave property is mirror reflection, or "parity." Physicists earlier found that wave symmetry in conventional, or singlet, superconductors is even. It is mathematically termed as +1. They also discovered that unconventional, or triplet, superconductor parity is odd, or - 1.

When singlets or triplets are reflected in a mirror, the reflected waves always have the same (+1) or opposite (-1) parity of the original waves.

Lebed finds that in strong magnetic fields, Cooper pair wave symmetries break down. The reflected waves don't look like the original waves. "It's like the Cooper pair wave sees someone else in the mirror," he said. "It's like Alice's adventure in a super-wonderland, where the mirrors are unusual and wrong."

"Because these Cooper pair electrons behave so differently than conventional singlet and unconventional triplet Cooper pairs, we call them 'exotic' Cooper pairs," he said.

Lebed provides a simple, whimsical picture to help explain the concept of this broken mirror symmetry.

BACK TO THE FUTURE, BACK TO THE PAST

UA physics graduate student Omjyoti Dutta and Lebed are now collaborating on more detailed theoretical studies of exotic superconducting phases. They have very recently discovered that "time-reversal" symmetry also breaks down in exotic Cooper pairs.

Time reversal symmetry is the idea that most fundamental physical laws would not change if time ran backwards instead of forward.

"This is the most fundamental symmetry in physics and breaks down only in some rare processes in high energy, or elementary particle, physics," Lebed said.

But the UA physicists find that time-reversal symmetry is broken because of the simultaneous rotating and non-rotating average spins of exotic Cooper pairs. "Half of the exotic Cooper pair electrons 'see' time directed from the past to the future, whereas the other half 'see' time directed from the future to the past," Lebed said.

"It's important to note that our theoretical results are very general," he said. "They are based on a mathematical theorem and have to be experimentally applied to most kinds of existing superconducting materials, including high-temperature superconductors."

The UA physicists are designing simple experiments for observing exotic superconductivity.

"We hope that our discovery of the exotic behavior of superconductivity in high magnetic fields eventually improves our understanding of how to most efficiently produce strong persistent currents in superconductors," Lebed said.

Superconductors are sought by energy, transportation, medical and computing industries. More practical, affordable superconductors would be a boon to power utilities that would realize enormous savings in more efficient systems for generating and storing electricity, to the transportation industry which is experimenting with trains that float above their tracks using superconducting magnets, to medical technologists who are developing improved magnetic resonance imaging, and to the supercomputing industry that seeks very fast electronic switches needed to build "petaflop" computers capable of performing a thousand-trillion floating point operations per second.

Lebed, who joined the UA in 2004, earned his doctorate in 1986 and his doctor of sciences degree (full professor accreditation) from the Landau Institute for Theoretical Physics and Moscow Institute for Physics and Technology in 2000. His research has influenced experiments conducted at Princeton University, Boston College, Harvard University, the National High Magnetic Field Laboratory, the Los Alamos National Laboratory and elsewhere.

Lori Stiles | University of Arizona
Further information:
http://uanews.org/silk/request/lebed_1591.jpg
http://uanews.org/silk/request/lebed_fig1.jpg
http://uanews.org/science

More articles from Physics and Astronomy:

nachricht Pulses of electrons manipulate nanomagnets and store information
21.07.2017 | American Institute of Physics

nachricht Vortex photons from electrons in circular motion
21.07.2017 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>