Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study finds physical link to strange electronic behavior

01.08.2014

Neutron measurements offer new clues about iron-based superconductor

Scientists have new clues this week about one of the baffling electronic properties of the iron-based high-temperature superconductor barium iron nickel arsenide. A Rice University-led team of U.S., German and Chinese physicists has published the first evidence, based on sophisticated neutron measurements, of a link between magnetic properties and the material's tendency, at sufficiently low temperatures, to become a better conductor of electricity in some directions than in others.

Anisotropic Infographic

Inelastic neutron scattering experiments revealed a temporary, collective anisotropic order prior to the onset of magnetism in a temperature interval where anisotropic resistance had previously been measured.

Credit: Tanyia Johnson/Rice University

The odd behavior, which has been documented in a number of materials, occurs at temperatures slightly higher than those needed to bring about magnetism; magnetism is believed to be essential for the origin of high-temperature superconductivity. In a new study appearing online this week in the journal Science Express, scientists at Rice, the Chinese Academy of Sciences in Beijing and Germany's Technische Universität München (TUM) offer the first evidence that the directionally dependent behavior arises from inherent physical properties of the material rather than from extraneous impurities, as had been previously suggested.

The new findings are based on sophisticated inelastic neutron-scattering experiments performed on several samples of barium iron nickel arsenide at the PUMA triple axis spectrometer at TUM's Heinz Maier-Leibnitz Zentrum in Garching, Germany. The research team said they hope the findings will prove useful in explaining the underlying physics of directionally dependent electronic phenomena that have been observed in several different types of superconducting materials.

"Most high-temperature superconductors, and many closely related compounds, exhibit a number of exotic electronic phases, particularly as they approach the critical temperature where superconductivity arises," said Pengcheng Dai, professor of physics and astronomy at Rice and the study's senior corresponding author. "Inelastic neutron scattering and other techniques are now allowing us to explore the physical basis of many of these phases."

Explaining high-temperature superconductivity remains the foremost challenge in condensed matter physics. First documented in 1986, the phenomenon is marked by zero electrical resistance in some crystalline ceramic materials below a critical temperature. While very cold, the critical temperatures for high-temperature superconductors -- between 50 and 150 kelvins above absolute zero -- are relatively high in comparison with the temperatures required for conventional superconductivity.

Like most high-temperature superconductors, barium iron nickel arsenide is a composite crystal. Its molecular structure consists of layers of arsenic and barium atoms that are sandwiched between checkerboard planes of iron atoms. The nickel atoms are then partially substituted for iron to tune the material's physical properties. The atoms in the crystals form an ordered pattern that looks identical in both the right-left (x-axis) and forward-back (y-axis) directions, but not in the up-down (z-axis).

At room temperature, the material acts as one might expect, conducting electricity equally well along both its x-axis and y-axis. However, as the material is cooled to near the critical temperature for magnetism, it passes through a phase where electrical resistance is higher in one direction than the other. Physicists call directionally dependent behavior "anisotropic resistance."

In the new study, Dai and colleagues bombarded crystals of barium iron nickel arsenide with neutrons. Neutron-scattering measurements can reveal the molecular structure of materials in great detail, and inelastic neutron-scattering tests allow physicists to see, among others, the vibrational properties of materials. In the magnetic inelastic scattering experiment at TUM, the incoming neutrons brought about short-lived magnetic waves in the crystals. Surprisingly, the intensity of these magnetic waves turned out to be different in the x and y directions. The experiments revealed that this directional dependence of magnetic excitations in the barium iron nickel arsenide occurs at precisely the same temperature range as the anisotropic resistance, thus establishing a crucial link between the two phenomena.

Rice theoretical physicist and study co-author Andriy Nevidomskyy, assistant professor of physics and astronomy, used the analogy of a crowd gathered at a stadium to watch a sporting event.

"During the game, all eyes are on the field, and this is an ordered state that describes all the individuals in the crowd in relation to one another," he said. "This state corresponds to the collective arrangement of electrons we see in magnetism and in superconductivity. The disordered arrangement we observe at room temperature, on the other hand, corresponds to the chaos we would see in the crowd one hour before the game begins, when people are turning from side to side and occasionally glancing at the field.

"The anisotropic state found in our study corresponds to a moment just before the kickoff, when the individuals are still looking in random directions but are aware that the game is about to start," Nevidomskyy said. "The incoming neutron pulse is the equivalent of someone blowing a whistle on the field. For a split second, the crowd reacts as one to the whistle, and every head turns to see if the game has begun. The individuals in the crowd quickly return to their random behavior, but the whistle has revealed an order that wasn't present an hour before."

The inelastic neutron scattering experiments uncovered an analogous behavior in the barium iron nickel arsenide. At high temperatures, the pulse of energy revealed no underlying order. The temporary, collective anisotropic order occurred only in the brief temperature interval prior to the onset of magnetism where the anisotropic resistance had previously been measured.

Rice theoretical physicist Qimiao Si, another study co-author, said the magnetic behavior observed by the inelastic neutron-scattering measurements reflects the way the spins of the electrons are dynamically organized in the material.

"This spin excitation anisotropy sheds new light on the microscopic origins of electronic phases in the iron pnictide superconductors," said Si, Rice's Harry C. and Olga K. Wiess Professor of Physics and Astronomy. "It may help explain the interplay between magnetism and superconductivity and, more generally, the mechanism for superconductivity, in the iron pnictide superconductors."

###

Study co-authors include Xingye Lu, Rui Zhang and Huiqian Luo, all of the Chinese Academy of Sciences, and J.T. Park of TUM's Heinz Maier-Leibnitz Zentrum. The research was funded by China's Ministry of Science and Technology, the National Natural Science Foundation of China, the Robert A. Welch Foundation, the National Science Foundation and the Alexander von Humboldt Foundation.

A high-resolution infographic is available for download at: http://news.rice.edu/wp-content/uploads/2014/07/AnistropyInHighTemp.pdf

Credit: Tanyia Johnson/Rice University

A copy of the Science Express paper is available at: http://www.sciencemag.org/content/early/recent

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,920 undergraduates and 2,567 graduate students, Rice's undergraduate student-to-faculty ratio is just over 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 2 for "best value" among private universities by Kiplinger's Personal Finance.

Jade Boyd | Eurek Alert!

More articles from Studies and Analyses:

nachricht A sudden drop in outdoor temperature increases the risk of respiratory infections
11.01.2017 | University of Gothenburg

nachricht Urbanization to convert 300,000 km2 of prime croplands
27.12.2016 | Mercator Research Institute on Global Commons and Climate Change (MCC) gGmbH

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

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

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>