PRESS-NEWS.org - Press Release Distribution
FREE PRESS RELEASES DISTRIBUTION

Dopants dramatically alter electronic structure of superconductor

Findings explain unusual properties, but complicate search for universal theory

2013-02-18
(Press-News.org) UPTON, NY - Over the last quarter century, scientists have discovered a handful of materials that can be converted from magnetic insulators or metals into "superconductors" able to carry electrical current with no energy loss-an enormously promising idea for new types of zero-resistance electronics and energy-storage and transmission systems. At present, a key step to achieving superconductivity (in addition to keeping the materials very cold) is to substitute a different kind of atom into some positions of the "parent" material's crystal framework. Until now, scientists thought this process, called doping, simply added more electrons or other charge carriers, thereby rendering the electronic environment more conducive to the formation of electron pairs that could move with no energy loss if the material is held at a certain chilly temperature.

Now, new studies of an iron-based superconductor by an international team of scientists - including physicists from the U.S. Department of Energy's Brookhaven National Laboratory and Cornell University - suggest that the story is somewhat more complicated. Their research, published online in Nature Physics February 17, 2013,* demonstrates that doping, in addition to adding electrons, dramatically alters the atomic-scale electronic structure of the parent material, with important consequences for the behavior of the current-carrying electrons.

"The key observation - that dopant atoms introduce elongated impurity states which scatter electrons in the material in an asymmetric way - helps explain most of the unusual properties," said J.C. Séamus Davis, the study's lead author, who directs the Center for Emergent Superconductivity at Brookhaven Lab and is also the J.G. White Distinguished Professor of Physical Sciences at Cornell University. "Our findings provide a new starting point for theorists trying to grapple with how these materials work, and could potentially point to new ways to design superconductors with improved properties," he said.

The researchers used a technique developed by Davis called spectroscopic imaging scanning tunneling microscopy to visualize the electronic properties around individual dopant atoms in the parent material, and to simultaneously monitor how electrons scatter around these dopants (in this case, cobalt).

Earlier studies had shown that certain electronic properties of the non-superconducting "parent" material had a strong directional dependence - for example, electrons were able to move more easily in one direction through the crystal than in the perpendicular direction. However, in those studies, the signal of a strong directional dependence only appeared when the scientists put the dopants into the material, and got stronger the more dopants they added.

Before this, the assumption was that dopants simply added electrons, and that the material's properties - including the emergence of superconductivity - were due to some intrinsic characteristic (for example, the alternating alignments of electron spins on adjacent atoms) that resulted in a directional dependence.

"But the emergence of directional dependence of electronic properties as more dopants are added suggests that the strong directionality is a result of the dopants, not an intrinsic property of the material," Davis said. "We decided to test this idea by directly imaging what each dopant atom does to the nearby atomic-level electronic structure in these materials."

According to Davis, the current paper reports two very clear results:

1) At each cobalt dopant atom, there is an elongated impurity state-a quantum mechanical state bound to the cobalt atom-that aligns in a particular direction (the same for each cobalt atom) relative to the overall crystal. 2) These oblong, aligned impurity states scatter the current-carrying electrons away from the impurity state in an asymmetric way - similar to the way ripples of water would propagate asymmetrically outward from an elongated stick thrown into a pond, rather than forming the circular pattern produced by a pebble.

"These direct observational findings explain most of the outstanding mysteries about how the electrical current moves through these materials - for example, with greater ease perpendicular to the direction you would expect based solely on the characteristics of the parent material," Davis said. "The results show that the dopants actually do dramatic things to the electronic structure of the parent material."

"It's possible that what we've found could be similar to an effect dopants had on early semiconductors," Davis said. "Early versions of these materials, though useful, had nowhere near the performance as those developed after the 1970s, when scientists at Bell Labs figured out a way to move the dopant atoms far away from the electrons so they wouldn't mess up the electronic structure." That advance made possible all the microelectronics we now use every day, including cell phones, he said.

"If we find out the dopant atoms are doing something we don't want in the iron and even copper superconductors, maybe we can find a way to move them away from the active electrons to make more useful materials."

### Brookhaven's role in this research was supported by the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center headquartered at Brookhaven National Laboratory. Additional funding was provided by the DOE Office of Science (Ames Laboratory), the National Science Foundation, the U.K. Engineering and Physical Sciences Research Council, the Scottish Funding Council, and the Netherlands Organization for Scientific Research.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization. Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more or follow Brookhaven Lab on Twitter. END



ELSE PRESS RELEASES FROM THIS DATE:

'Snooze button' on biological clocks improves cell adaptability

2013-02-18
The circadian clocks that control and influence dozens of basic biological processes have an unexpected "snooze button" that helps cells adapt to changes in their environment. A study by Vanderbilt University researchers published online Feb. 17 by the journal Nature provides compelling new evidence that at least some species can alter the way that their biological clocks function by using different "synonyms" that exist in the genetic code. "This provides organisms with a novel and previously unappreciated mechanism for responding to changes in their environment," said ...

Microbes team up to boost plants' stress tolerance

2013-02-18
UNIVERSITY PARK, PA. -- While most farmers consider viruses and fungi potential threats to their crops, these microbes can help wild plants adapt to extreme conditions, according to a Penn State virologist. Discovering how microbes collaborate to improve the hardiness of plants is a key to sustainable agriculture that can help meet increasing food demands, in addition to avoiding possible conflicts over scare resources, said Marilyn Roossinck, professor of plant pathology and environmental microbiology, and biology. "It's a security issue," Roossinck said. "The amount ...

Ancient teeth bacteria record disease evolution

2013-02-18
DNA preserved in calcified bacteria on the teeth of ancient human skeletons has shed light on the health consequences of the evolving diet and behaviour from the Stone Age to the modern day. The ancient genetic record reveals the negative changes in oral bacteria brought about by the dietary shifts as humans became farmers, and later with the introduction of food manufacturing in the Industrial Revolution. An international team, led by the University of Adelaide's Centre for Ancient DNA (ACAD) where the research was performed, has published the results in Nature Genetics ...

Wiring the ocean

2013-02-18
For most people, the sea is a deep, dark mystery. That is changing, though, as scientists find innovative ways to track the movements of ocean-going creatures. Stanford marine sciences professor and Stanford Woods Institute Senior Fellow Barbara Block is using technology to enable live feeds of animal movements relayed by a series of "ocean WiFi hotspots." This could help protect marine ecosystems by revolutionizing how we understand their function, population structure, fisheries management and species' physiological and evolutionary constraints. Block will explain ...

Excessive TV in childhood linked to long-term antisocial behaviour

2013-02-18
Children and adolescents who watch a lot of television are more likely to manifest antisocial and criminal behaviour when they become adults, according to a new University of Otago, New Zealand, study published online in the US journal Pediatrics. The study followed a group of around 1000 children born in the New Zealand city of Dunedin in 1972-73. Every two years between the ages of 5 and 15, they were asked how much television they watched. Those who watched more television were more likely to have a criminal conviction and were also more likely to have antisocial ...

Pathway controlling cell growth revealed

Pathway controlling cell growth revealed
2013-02-18
A Melbourne-based research team has discovered a genetic defect that can halt cell growth and force cells into a death-evading survival state. The finding has revealed an important mechanism controlling the growth of rapidly-dividing cells that may ultimately lead to the development of new treatments for diseases including cancer. The discovery was made by Associate Professor Joan Heath, Dr Yeliz Boglev and colleagues at the Melbourne-Parkville Branch of the Ludwig Institute for Cancer Research. Dr Kate Hannan, Associate Professor Rick Pearson and Associate Professor ...

Douglas A. Melton to Keynote present at Stem Cell Summit - Apr 2013 in Boston MA

2013-02-18
Douglas A. Melton will give a keynote presentation on "How To Make Pancreatic Beta Cells" at the Stem Cell Summit 2013 (Apr 29-30, 2013 in Boston MA). Dr. Melton's presentation will focus on the research of making human pancreatic beta cells to study and treat diabetes. This goal is pursued with two main approaches: directing the differentiation of stem cells into beta cells and studying the signals that replicate pre-existing beta cells. The signals that direct stem and progenitor cells toward a mature beta cell phenotype will be described as well as work ...

Abbey Design Center Wins Talk of the Town Award for Customer Satisfaction

2013-02-18
Achieving the highest customer satisfaction rating of 5 stars, Abbey Design Center has won the prestigious CMUS Talk of the Town Customer Satisfaction Award in the Home Improvement & Remodeling category. The Talk of the Town Awards, presented by Talk of the Town News, Customer Care News magazine and Celebration Media U.S. (CMUS), honor companies and professionals that provide excellent customer service as reported by their customers through no-cost, user-review websites, blogs, social networks, business rating services, and other honors and accolades. This data ...

Tennessee Roofer Creates New Nashville Focused Consumer Website

2013-02-18
Nashville Roofing Master, a Tennessee based roofing contractor, has announced the creation of a new website. The new site, Roofing-Nashville.net, is designed to provide consumer advice for homeowners and residents of the Nashville metro area and the surrounding region. The site features articles on various topics which will be of interest to people who need a new roof or repairs to their current roof. Prior to launching the new site, Roofing Master had a site which was more focused on marketing the strengths of the company, but which didn't have any content featuring ...

League of Women Voters of Bergen County to Celebrate Women's History Month and League's 93rd Birthday

2013-02-18
The League of Women Voters of Bergen County will hold its annual commemoration of Women's History Month and observe the League's 93rd birthday with a special celebration on Sunday, March 3, 2 to 4 p.m., at the Park Ridge Community Center, 53 Park Avenue, Park Ridge, New Jersey. The entrance to the library on the lower level should be used. The celebration is free and open to the public. The audience is invited to participate in the program and to select and discuss briefly a woman in current or past United States history, whom they admire. At previous celebrations, contenders ...

LAST 30 PRESS RELEASES:

Scientists model 'true prevalence' of COVID-19 throughout pandemic

New breakthrough to help immune systems in the fight against cancer

Through the thin-film glass, researchers spot a new liquid phase

Administering opioids to pregnant mice alters behavior and gene expression in offspring

Brain's 'memory center' needed to recognize image sequences but not single sights

Safety of second dose of mRNA COVID-19 vaccines after first-dose allergic reactions

Changes in disparities in access to care, health after Medicare eligibility

Use of high-risk medications among lonely older adults

65+ and lonely? Don't talk to your doctor about another prescription

Exosome formulation developed to deliver antibodies for choroidal neovascularization therapy

Second COVID-19 mRNA vaccine dose found safe following allergic reactions to first dose

Plant root-associated bacteria preferentially colonize their native host-plant roots

Rare inherited variants in previously unsuspected genes may confer significant risk for autism

International experts call for a unified public health response to NAFLD and NASH epidemic

International collaboration of scientists rewrite the rulebook of flowering plant genetics

Improving air quality reduces dementia risk, multiple studies suggest

Misplaced trust: When trust in science fosters pseudoscience

Two types of blood pressure meds prevent heart events equally, but side effects differ

New statement provides path to include ethnicity, ancestry, race in genomic research

Among effective antihypertensive drugs, less popular choice is slightly safer

Juicy past of favorite Okinawan fruit revealed

Anticipate a resurgence of respiratory viruses in young children

Anxiety, depression, burnout rising as college students prepare to return to campus

Goal-setting and positive parent-child relationships reduce risk of youth vaping

New research identifies cancer types with little survival improvements in adolescents and young adul

Oncotarget: Replication-stress sensitivity in breast cancer cells

Oncotarget: TERT and its binding protein: overexpression of GABPA/B in gliomas

Development of a novel technology to check body temperature with smartphone camera

The mechanics of puncture finally explained

Extreme heat, dry summers main cause of tree death in Colorado's subalpine forests

[Press-News.org] Dopants dramatically alter electronic structure of superconductor
Findings explain unusual properties, but complicate search for universal theory