Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists reveal effects of quantum 'traffic jam' in high-temperature superconductors

01.09.2008
Findings may point to new materials to get the current flowing at higher temperatures

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.

"We've made movies to show this traffic jam as a function of energy. At some energies, the traffic is moving and at others the electron traffic is completely blocked," said physicist J.C. Seamus Davis of Brookhaven National Laboratory and Cornell University, lead author on the paper. Davis will be giving a Pagels Memorial Public Lecture to announce these results at the Aspen Center for Physics on August 27.

Understanding the detailed mechanism for how quantum traffic jams (technically referred to as "Mottness" after the late Sir Neville Mott of Cambridge, UK) impact superconductivity in cuprates may point scientists toward new materials that can be made to act as superconductors at significantly higher temperatures suitable for real-world applications such as zero-loss energy generation and transmission systems and more powerful computers.

The idea that increasing binding energy could elevate a superconductor's transition temperature stems from the mechanism underlying conventional superconductors' ability to carry current with no resistance. In those materials, which operate close to absolute zero (0 kelvin, or -273 degrees Celsius), electrons carry current by forming so-called Cooper pairs. The more strongly bound those electron pairs, the higher the transition temperature of the superconductor.

But unlike those metallic superconductors, the newer forms of high-temperature superconductors, first discovered some 20 years ago, originate from non-metallic, Mott-insulating materials. Elevating these materials' pair-binding energy only appears to push the transition temperature farther down, closer to absolute zero rather than toward the desired goal of room temperature or above.

"It has been a frustrating and embarrassing problem to explain why this is the case," Davis said. Davis's research now offers an explanation.

In the insulating "parent" materials from which high-temperature superconductors arise, which are typically made of materials containing copper and oxygen, each copper atom has one "free" electron. These electrons, however, are stuck in a Mott insulating state -- the quantum traffic jam -- and cannot move around. By removing a few of the electrons — a process called "hole doping" -- the remaining electrons can start to flow from one copper atom to the next. In essence, this turns the material from an insulator to a metallic state, but one with the startling property that it superconducts -- it carries electrical current effortlessly without any losses of energy.

"It's like taking some cars off the highway during rush hour. All of a sudden, the traffic starts to move," said Davis.

The proposed mechanism for how these materials carry the current depends on magnetic interactions between the electrons causing them to form superconducting Cooper pairs. Davis's research, which used "quasiparticle interference imaging" with a scanning tunneling microscope to study the electronic structure of a cuprate superconductor, indicates that those magnetic interactions get stronger as you remove holes from the system. So, even as the binding energy, or ability of electrons to link up in pairs, gets higher, the "Mottness," or quantum traffic-jam effect, increases even more rapidly and diminishes the ability of the supercurrent to flow.

"In essence, the research shows that what is believed to be required to increase the superconductivity in these systems — stronger magnetic interactions -- also pushes the system closer to the 'quantum traffic-jam' status, where lack of holes locks the electrons into positions from which they cannot move. It's like gassing up the cars and then jamming them all onto the highway at once. There's lots of energy, but no ability to go anywhere," Davis said.

With this evidence pointing the scientists to a more precise theoretical understanding of the problem, they can now begin to explore solutions. "We need to look for materials with such strong pairing but which don't exhibit this Mottness or 'quantum traffic-jam' effect," Davis said.

Scientists at Brookhaven are now investigating promising new materials in which the basic elements are iron and arsenic instead of copper and oxygen. "Our hope is that they will have less 'traffic-jam' effect while having stronger electron pairing," Davis said. Techniques developed for the current study should allow them to find out.

Karen McNulty Walsh | EurekAlert!
Further information:
http://www.bnl.gov
http://www.bnl.gov/newsroom

More articles from Physics and Astronomy:

nachricht On Mars, sands shift to a different drum
24.05.2019 | University of Arizona

nachricht New Boost for ToCoTronics
23.05.2019 | Julius-Maximilians-Universität Würzburg

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: New studies increase confidence in NASA's measure of Earth's temperature

A new assessment of NASA's record of global temperatures revealed that the agency's estimate of Earth's long-term temperature rise in recent decades is accurate to within less than a tenth of a degree Fahrenheit, providing confidence that past and future research is correctly capturing rising surface temperatures.

The most complete assessment ever of statistical uncertainty within the GISS Surface Temperature Analysis (GISTEMP) data product shows that the annual values...

Im Focus: The geometry of an electron determined for the first time

Physicists at the University of Basel are able to show for the first time how a single electron looks in an artificial atom. A newly developed method enables them to show the probability of an electron being present in a space. This allows improved control of electron spins, which could serve as the smallest information unit in a future quantum computer. The experiments were published in Physical Review Letters and the related theory in Physical Review B.

The spin of an electron is a promising candidate for use as the smallest information unit (qubit) of a quantum computer. Controlling and switching this spin or...

Im Focus: Self-repairing batteries

UTokyo engineers develop a way to create high-capacity long-life batteries

Engineers at the University of Tokyo continually pioneer new ways to improve battery technology. Professor Atsuo Yamada and his team recently developed a...

Im Focus: Quantum Cloud Computing with Self-Check

With a quantum coprocessor in the cloud, physicists from Innsbruck, Austria, open the door to the simulation of previously unsolvable problems in chemistry, materials research or high-energy physics. The research groups led by Rainer Blatt and Peter Zoller report in the journal Nature how they simulated particle physics phenomena on 20 quantum bits and how the quantum simulator self-verified the result for the first time.

Many scientists are currently working on investigating how quantum advantage can be exploited on hardware already available today. Three years ago, physicists...

Im Focus: Accelerating quantum technologies with materials processing at the atomic scale

'Quantum technologies' utilise the unique phenomena of quantum superposition and entanglement to encode and process information, with potentially profound benefits to a wide range of information technologies from communications to sensing and computing.

However a major challenge in developing these technologies is that the quantum phenomena are very fragile, and only a handful of physical systems have been...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

 
Latest News

On Mars, sands shift to a different drum

24.05.2019 | Physics and Astronomy

Piedmont Atlanta first in Georgia to offer new minimally invasive treatment for emphysema

24.05.2019 | Medical Engineering

Chemical juggling with three particles

24.05.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>