Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Two Spin Liquids Square Off in an Iron-Based Superconductor

07.08.2015

Despite a quarter-century of research since the discovery of the first high-temperature superconductors, scientists still don't have a clear picture of how these materials are able to conduct electricity with no energy loss. Studies to date have focused on finding long-range electronic and magnetic order in the materials, such as patterns of electron spins, based on the belief that this order underlies superconductivity. But a new study published online the week of August 3, 2015, in the Proceedings of the National Academy of Sciences is challenging this notion.

The study, conducted by researchers from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Oak Ridge National Laboratory (ORNL), describes how an iron-telluride material related to a family of high-temperature superconductors develops superconductivity with no long-range electronic or magnetic order when "doped" with a small amount of sulfur. In fact, the material displays a liquid-like magnetic state consisting of two coexisting and competing disordered magnetic phases, which appears to precede-and may be linked to-its superconducting behavior.


Brookhaven National Laboratory

Model electron spin maps of the iron-tellurium-sulfur material. The left-hand column, a-c, shows three models of electron spin correlations, with the red and green colors of the peaks and corresponding planar projections below each model representing oppositely oriented spins. The images on the right, d-f, show the resulting neutron scattering patterns for each case. Starting at a, which represents the dominant correlations at high temperature, notice how the spins form alternating squares like a checkerboard in the planar projection, and how the "square dance partners" of the pattern change to diagonals in (b), which occurs on cooling to low temperature, and finally to alternating stripes stipulated to exist in a good superconductor (c).

"Our results challenge a number of widely accepted paradigms into how unconventional superconductors work," said the study's lead researcher, Brookhaven physicist Igor Zaliznyak. "I believe that we have uncovered an important clue to the nature of magnetism and its connections to superconductivity in the iron-based superconductors."

This advance could open up a new avenue for exploring the emergence of a property with great potential for widespread use. Conventional superconductors, which must be chilled to extremely low temperatures to operate, already play a key role in many modern technologies, from medical magnetic resonance imaging (MRI) to maglev trains.

New clues about the function of unconventional superconductors, which do not need to be super-cooled, could lead to many more technologies, including, potentially, zero-energy-loss power transmission lines and other important energy applications. Indeed, other materials based upon a similar structure as the material studied here can operate as superconductors at these "warmer" temperatures, so understanding the physics of this close relative has many important implications.

A magnetic square dance

Zaliznyak and his collaborators studied the unconventional superconducting material, made of iron and tellurium (FeTe), using neutron scattering at ORNL's High Flux Isotope Reactor, a DOE Office of Science User Facility. They created maps of magnetic scattering for the material for several temperatures and as the material was doped with a small amount of sulfur. Like a composite photograph made of several separate photos, the maps stitch together many "snapshots" of the magnetic order in the material.

They found that the ordering was extremely local in nature, existing for only an instant before changing-a characteristic of a liquid-like behavior. In fact, the results revealed that a fundamental change in the local, liquid-like pattern of electronic spin correlations was the key change that accompanied the emergence of superconductivity with decreasing temperature in this material.

"The measurements reveal dynamical arrangements of magnetic moments similar to the patterns formed by square dancers on a dance floor," said Zaliznyak. "As the temperature was reduced, the magnetic atoms appeared to change their partners; in this case, the dance move was initiated by the mobile electrons that eventually develop into the superconducting state."

A rare look at the liquid state

In addition to offering insight into a potential mechanism for the emergence of high-temperature superconductivity, this work also provides valuable insight into the nature of liquids. Despite being among the most common condensed matter systems-we are surrounded by and largely made of water-liquids are still poorly understood at the microscopic level. In fact, the dynamic and fleeting nature of the local order in liquids is what makes them particularly difficult to study.

The idea that liquids can be a mixture of two distinct liquid "species" that have different local structures and densities dates back to the late nineteenth century. Even now, the possible existence of different liquid "polymorphs" in simple molecular fluids, and liquid-liquid phase transitions between them, continues to receive considerable attention in the research world. But the issue has not been settled, mainly because the competition between different liquid phases only arises at very low temperatures, often far below freezing.

"In some materials, however, such competition arises quite naturally in systems of electronic magnetic moments, where the development of magnetic order is hindered by competing interactions," said Zaliznyak. "In these cases, the material remains disordered even at temperatures much lower than the energy of magnetic interactions, thus producing an electronic spin liquid state."

"Our results studying the spin system of sulfur-doped FeTe provide a rare experimental example of such a liquid polymorphism."

More unexpected insights

The group's results also refute another set of widely accepted views of the electronic states in metals, where electrons are only allowed to occupy a certain set of rigid energy bands. The spin-liquid state they discovered seems to reflect the existence of new electron-orbital hybrids, likely resulting from the sulfur doping but also brought on by changes in temperature.

"This is a surprising discovery that calls for a profound revision of the 'tight binding' model of electron orbitals," said Zaliznyak.

He and his group also may have found an explanation for mysterious neutron scattering patterns observed by other groups studying iron-based superconductor samples.

"It appears that all of the variety in the neutron patterns that have been observed in these materials can be well described by our spin-liquid model," he said. "They all manifest with very similar local correlations, revealing that we may have found an amazing intrinsic universality among them."

Zaliznyak conceived the experiments and performed the neutron scattering measurements with ORNL's Andrei Savici and ORNL instrumentation scientist Mark Lumsden on materials synthesized by Rongwei Hu and Cedomir Petrovic in Brookhaven's Condensed Matter Physics and Materials Science Department. Brookhaven Lab theoretical physicist Alexei Tsvelik provided theoretical support and guidance throughout the project.

"Theoretical validation of new ideas was absolutely essential to our success," Zaliznyak said.

The work at Brookhaven was supported by the U.S. Department of Energy's Office of Science (Office of Basic Energy Sciences), in part through the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center. Research at ORNL was sponsored by the Scientific User Facilities Division within the Office of Basic Energy Sciences.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The 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 science.energy.gov.

Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more at http://www.bnl.gov/newsroom ; follow Brookhaven Lab on Twitter, http://twitter.com/BrookhavenLab ; find us on Facebook, http://www.facebook.com/BrookhavenLab ; and join us on Tumblr, http://brookhavenlab.tumblr.com .

Karen Walsh | newswise

More articles from Materials Sciences:

nachricht InLight study: insights into chemical processes using light
05.12.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Physics, photosynthesis and solar cells
01.12.2016 | University of California - Riverside

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

High-precision magnetic field sensing

05.12.2016 | Power and Electrical Engineering

Construction of practical quantum computers radically simplified

05.12.2016 | Information Technology

NASA's AIM observes early noctilucent ice clouds over Antarctica

05.12.2016 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>