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 New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

nachricht Reusable carbon nanotubes could be the water filter of the future, says RIT study
30.03.2017 | Rochester Institute of Technology

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>