Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Evidence to Aid Search for Charge “Stripes” in Superconductors

11.09.2013
Findings identify signature that will help scientists investigate and understand materials that carry current with no resistance

A team of scientists from Columbia University’s School of Engineering and Applied Science and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have identified a series of clues that particular arrangements of electrical charges known as “stripes” may play a role in superconductivity—the ability of some materials to carry electric current with no energy loss.

But uncovering the detailed relationship between these stripe patterns and the appearance or disappearance of superconductivity is extremely difficult, particularly because the stripes that may accompany superconductivity are very likely moving, or fluctuating.

As a step toward solving this problem, the Brookhaven team used an indirect method to detect fluctuating stripes of charge density in a material closely related to a superconductor. The research, described in a paper published in Physical Review Letters August 30, 2013, identifies a key signature to look for in superconductors as scientists seek ways to better understand and engineer these materials for future energy-saving applications.

“The charge stripes are hard to see even when they are frozen,” said Simon Billinge, who holds a joint appointment between Columbia Engineering and Brookhaven Lab, and leads the collaboration that performed this study. “But they are impossible to see when they are moving. Tantalizingly, they always tend to show up in the vicinity of superconductivity, but we don’t know what their role is in this phenomenon.”

“In previous experiments, we’ve seen evidence of fluctuating ‘magnetic spin’ stripes—patterns of how adjacent atoms’ spin directions are arranged—that are compatible with superconductivity,” added Brookhaven physicist John Tranquada, a senior collaborator on the research team. “Now we’re trying to look at the arrangements of charge density, to see if there are alternating stripes of densely and more loosely packed charges. The charge part is harder to see.”

To get an idea of the difficulty of tracking moving stripes, think of the cars in a supermarket parking lot. The lines delineating the parking spots are like the positions of atoms making up a crystal, and the cars are like the electrons. If there’s a pattern to the arrangement—say alternating colors of cars in adjacent spots—it would be easy to spot in a single snapshot. But if you took a single photo (with a very long exposure) over the course of a busy shopping day as cars moved into and out of spots, all you’d see is a blur. You wouldn’t be able to tell if they continued to park in alternating order, if the details of the parking pattern were changing, or even whether there was a pattern at all.

A series of individual snapshots might make the details more discernable. But in the case of analyzing materials science samples, the “snapshots” are often made with very intense x-rays or neutron beams. And access to beam time at these imaging facilities is limited, and expensive. “You can’t throw enough ‘light’ on the problem to see it,” Tranquada said.

Instead, the scientists tried a completely different approach. Rather than looking directly at the stripes, they looked for a telltale signal that indicates the presence of the stripes by association, but in a different measurement that can be done quickly and with much less precious beam time. They started these experiments on a material they knew had a static striped pattern below a certain temperature to make sure that the signal was evident in this new measurement. They then studied what happened as the temperature rose to see whether the stripes would either disappear or persist but start to move.

The scientists ground up crystals of the test material into a fine powder and placed samples of it in line with a beam of neutrons at the Los Alamos Neutron Scattering Center at Los Alamos National Laboratory. Similar to the way light reflecting off an object enters your eyes to create an image, the neutron beams diffracted by the crystals’ atoms yield information about the positions of the atoms. The scientists used that information to infer the material’s electronic structure, and repeated the experiment at gradually warmer temperatures.

“We’re looking at the average crystal structure, the height-to-width aspect ratio of that structure, and how different the positions of the atoms are from that average,” said Milinda Abeykoon, lead author on the paper.

In the static striped arrangement, the atoms are displaced from the average in a regular way—like parking spots that are alternatingly wider or narrower than average. Such atomic displacements force the electrons to follow a stripe-ordered arrangement—the way smaller cars would fill the narrow parking spots alternating with wider SUVs.

With increasing temperature, the scientists found that while the aspect ratio of the crystal structure changed, the displacements from average structure persisted, leading them to conclude by inference that the striped pattern of charge density also remained, even though it was no longer static.

“This is the first powder diffraction scattering evidence for fluctuating charge stripes above the temperature where we see static order,” said co-author Simon Billinge, referring to the new measurement. Billinge is professor of materials science and applied physics and applied mathematics at Columbia Engineering, and a scientist at Brookhaven Lab.

“One of the most critical aspects of this experiment is that we had lots of different data points, lots of temperatures—so you can catch small deviations,” said co-author Emil Bozin of Brookhaven. He also noted how improvements in detector technology made it possible to collect a lot of data within a fixed amount of time. “Ten years ago we would have needed a couple of weeks of beam time to do this experiment; we collected all our data in just a few days.”

The next step: Return to searching for stripes in superconductors. “This model system teaches us what diffraction-scattering signature to look for in copper-based superconductors to see if these fluctuations exist,” Bozin said.

That search should lead to better understanding of the role of stripes in superconductivity, and possibly to new approaches to engineer advanced superconductors for energy applications.

Additional collaborators on this study are Wei-Guo Yin, Genda Gu, and John Hill of Brookhaven.

This research was funded by the DOE Office of Science.

Holly Evarts | Newswise
Further information:
http://www.columbia.edu

More articles from Materials Sciences:

nachricht One in 5 materials chemistry papers may be wrong, study suggests
15.12.2017 | Georgia Institute of Technology

nachricht Scientists channel graphene to understand filtration and ion transport into cells
11.12.2017 | National Institute of Standards and Technology (NIST)

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Error-free into the Quantum Computer Age

A study carried out by an international team of researchers and published in the journal Physical Review X shows that ion-trap technologies available today are suitable for building large-scale quantum computers. The scientists introduce trapped-ion quantum error correction protocols that detect and correct processing errors.

In order to reach their full potential, today’s quantum computer prototypes have to meet specific criteria: First, they have to be made bigger, which means...

Im Focus: Search for planets with Carmenes successful

German and Spanish researchers plan, build and use modern spectrograph

Since 2016, German and Spanish researchers, among them scientists from the University of Göttingen, have been hunting for exoplanets with the “Carmenes”...

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Error-free into the Quantum Computer Age

18.12.2017 | Physics and Astronomy

Disarray in the brain

18.12.2017 | Studies and Analyses

2 million euros in funding for new MR-compatible electrophysiological brain implants

18.12.2017 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>