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    The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
    • 2018-07-06 16:30:02
    • Article ID: 697116

    Electrons Slowing Down at Critical Moments

    • Credit: Argonne National Laboratory

      Electrons in some oxides can experience an “unconventional slowing down” of their response to a light pulse, according to Argonne material scientists and their collaborators. This surprising behavior may result in useful properties related to magnetism, conductivity or even superconductivity.

    In a new study, researchers from the U.S. Department of Energy’s (DOE) Argonne National Laboratory have determined that electrons in some oxides can experience an “unconventional slowing down” of their response to a light pulse.

    The researchers describe the behavior as lasting about a millionth of a second, which is still a million times slower than traditional electronic recovery times.

    “We’ve discovered that electrons can be very slow to return to their homes after being kicked out from the ‘ordered states.’” — Haidan Wen, Argonne physicist and co-author

    “It’s as if the electron is spending two years or more dithering between states when normally it could make up its mind in a minute,” said Anand Bhattacharya, an Argonne materials scientist and co-author of the study, published May 4, in Nature Communications.

    In a crystal, all the atoms form a periodic structure called a lattice, where the atoms are arranged in a repetitive pattern in three dimensions. The properties of electrons living in this space typically obey the same periodicity.

    But below a temperature of about minus 100 degrees Fahrenheit, the electrons in the study material, lanthanum strontium ferrite, find it more energetically advantageous to cooperate with the lattice and magnetism on the iron atoms, to form a new periodic structure called a magnetically driven, charge-ordered state.

    The behavior occurs close to a temperature that marks a phase transition — similar to the way in which 32 degrees Fahrenheit marks the phase transition from water to ice. But the phase transition studied here is peculiar because it marks a transition between a magnetic insulator and a non-magnetic metal. According to Bhattacharya, these sorts of phase transitions are potentially useful as 'switches,' where a material’s 'on' and 'off' states can allow us to toggle between metals, insulators, magnets and superconductors.

    However, the material studied — known as La1/3Sr2/3FeO3 — had a surprise in store.

    “We’ve discovered that electrons can be very slow to return to their homes after being kicked out from the ‘ordered states,’ taking much longer than we previously anticipated,” said Argonne physicist Haidan Wen, another co-author.

    Because the electrons are lighter than the atoms in the lattice, they usually react more quickly to the light pulse, settling into their new state before the lattice comes to rest. But in this case, the electronic recovery lasts much longer than the lattice recovery, as determined through experiments conducted at the Advanced Photon Source’s (APS) beamline 7ID-C and at the Center for Nanoscale Materials (CNM), both DOE Office of Science User Facilities.

    The researchers conducted transient optical reflectivity measurements at CNM with Argonne scientist Richard Schaller and observed that, as the temperature approaches the phase transition, the electron relaxation slows down by orders of magnitude. Complementary hard X-ray diffraction at the APS measured structural changes to determine how quickly the lattice and charge-ordered phase evolved.

    According to the authors of the paper, the abnormal behavior of electrons is likely a result of magnetic interactions. Conventionally, the two regions on either side of a first-order phase transition are quite distinct, like water and ice. However, Argonne theorist Hyowon Park, who holds a joint appointment with the University of Illinois at Chicago, found that, due to magnetic interactions close to the phase transition, there are actually two different kinds of charge-ordered states.

    When the excited electrons try to go back to the charge-ordered phase, they find a very shallow downhill slope into one of the two charge-ordered states, which ultimately slows down the ordering processes. Further experimental work would be needed to gain microscopic insights on exactly how the electrons organize themselves spatially between these two charge-ordered states.

    For both Bhattacharya and Wen, understanding these “slow” processes in the realm of ultrafast phenomena may offer new ways to stabilize or increase the lifetime of exotic transient states that occur after a material is hit with a light pulse. Such insights may reveal potentially useful properties related to magnetism, conductivity or even superconductivity.

    The researchers also used Argonne’s Laboratory Computing Resource Center. Other co-authors are from the University of Illinois at Chicago, Northwestern University and Dublin City University.

    The study, titled “Unconventional slowing down of electronic recovery in photoexcited charge-ordered La1/3Sr2/3FeO3” was funded by the DOE Office of Science, Basic Energy Sciences, as well as the University of Illinois at Chicago.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

    The U.S. Department of Energy'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, visit the Office of Science website.

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    Seeing a Salt Solution's Structure Supports One Hypothesis About How Minerals Form

    Oak Ridge National Laboratory scientists used neutrons, isotopes and simulations to "see" the atomic structure of a saturated solution and found evidence supporting one of two competing hypotheses about how ions come together to form minerals.

    New PMLD Technique Improves Tools to Form Organic Multilayers

    Researchers have developed a new class of molecular layer deposition chemistry that paves the way for a new photoactivated molecular layer deposition technique. They report that their new method will expand the tool kit for forming covalently bound organic multilayers at surfaces. These emerging deposition techniques have enabled engineers to produce organic thin films with improved conformality. Richard Closser, Stanford University, will present the findings at the AVS 65th International Symposium and Exhibition, Oct. 21-26, 2018.

    Spotlighting Differences in Closely-Related Species

    Aspergillus fungi play roles in fields including bioenergy, health, and biotechnology. In Nature Genetics, a team led by scientists at the Technical University of Denmark, the DOE Joint Genome Institute, and the Joint Bioenergy Institute, present the first large analysis of an Aspergillus fungal subgroup, section Nigri.

    Researchers switch material from one state to another with a single flash of light

    Scientists from the Department of Energy's SLAC National Accelerator Laboratory and the Massachusetts Institute of Technology have demonstrated a surprisingly simple way of flipping a material from one state into another, and then back again, with single flashes of laser light.

    The Stories Behind the Science: How Does the Ocean's Saltiness Affect Tropical Storms?

    Two researchers with personal experience of hurricanes set out to investigate the role of an underestimated factor in storm's strength - salinity. They found that salinity plays a larger role than anyone thought, including them.

    Surprise finding: Discovering a previously unknown role for a source of magnetic fields

    Feature describes unexpected discovery of a role the process that seeds magnetic fields plays in mediating a phenomenon that occurs throughout the universe and can disrupt cell phone service and knock out power grids on Earth.

    Genetic behavior reveals cause of death in poplars essential to ecosystems, industry

    Scientists studying a valuable, but vulnerable, species of poplar have identified the genetic mechanism responsible for the species' inability to resist a pervasive and deadly disease. Their finding could lead to more successful hybrid poplar varieties for increased biofuels and forestry production and protect native trees against infection.

    Pushing the (Extra Cold) Frontiers of Superconducting Science

    Ames Laboratory has developed a method to measure magnetic properties of superconducting and magnetic materials that exhibit unusual quantum behavior at very low temperatures in high magnetic fields.

    Scientists Find Unusual Behavior in Topological Material

    Argonne scientists have identified a new class of topological materials made by inserting transition metal atoms into the atomic lattice of a well-known two-dimensional material.

    Wind Farms and Reducing Hurricane Precipitation

    New research reveals an unexpected benefit of large-scale offshore wind farms: the ability to lessen precipitation from hurricanes.


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    Physicist Takes Cues from Artificial Intelligence

    In the world of computing, there's a groundswell of excitement for what is perceived as the impending revolution in artificial intelligence. Like the industrial revolution in the 19th century and the digital revolution in the 20th, the AI revolution is expected to change the way we live and work. Now, Cristiano Fanelli aims to bring the AI revolution to nuclear physics.

    Engineering professor receives Department of Energy grant

    New Mexico State University Department of Civil Engineering Assistant Professor Ehsan Dehghan Niri has received a United States Department of Energy grant. This is a three-year award for $400,000 and is a collaboration with Arizona State University.

    Argonne and Capstone receive funding to advance thermal energy storage technology

    The U.S. Department of Energy's (DOE) Argonne National Laboratory and Capstone Turbine Corp. have received $380,000 in DOE Technology Commercialization Funding to refine Argonne's high-efficiency, fast charging/discharging latent heat thermal energy storage system (TESS) for use in building applications and process/manufacturing industries.

    AVS and AIP Publishing Expand Partnership to Launch AVS Quantum Science

    AIP Publishing and AVS: Science and Technology of Materials, Interfaces, and Processing (AVS) today announced an agreement to publish AVS Quantum Science, a new online interdisciplinary journal. The announcement coincides with the AVS 65th International Symposium & Exhibition in Long Beach, California, from October 21-26, 2018.

    Prototype Solar Energy, Battery Systems to Fuel Commercialization

    Designing, building and testing prototype systems that show how renewable energy can power devices, such as a weather and soil sensor station, can help bridge the gap between basic science research and commercialization.

    Argonne to Advance High Performance Computing in Manufacturing

    Argonne awarded funding to partner with Industry to advance the use of high performance computing in manufacturing.

    "Invisible Glass" Wins 2018 Create the Future Design Contest Grand Prize

    Scientists from the Center for Functional Nanomaterials developed a technique for making nonreflecting glass, silicon, and plastic surfaces.

    Missouri S&T researchers win multimillion dollar grant to build fast-charging stations for electric cars

    Researchers from Missouri S&T and three private companies will combine their expertise to create charging stations for electric vehicles that could charge a car in less than 10 minutes - matching the time it takes to fill up a conventional vehicle with gasoline."The big problem with electric vehicles is range, and it's not so much range as range anxiety.

    Making batteries store more energy, last longer

    A new solid polymer electrolyte may help make cell phone batteries store more energy and last longer.

    Three Brookhaven Lab Scientists Named Fellows of American Physical Society

    The American Physical Society (APS), the world's largest physics organization, has elected three scientists from the U.S. Department of Energy's (DOE) Brookhaven National Laboratory as 2018 APS fellows.


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    Cryocooler Cools an Accelerator Cavity

    Researchers demonstrated cryogen-free operation of a superconducting radio-frequency cavity that might ease barriers to its use in societal applications.

    Shining Light on the Separation of Rare Earth Metals

    New studies identify key molecular characteristics to potentially separate rare earth metals cleanly and efficiently with light.

    Placing Atoms for Optimum Catalysts

    Precise positioning of oxygens could help engineer faster, more efficient energy-relevant chemical transformations.

    How to Make Soot and Stardust

    Scientists unlock mystery that could help reduce emissions of fine particles from combustion engines and other sources.

    Breaking the Symmetry Between Fundamental Forces

    Scientists improve our understanding of the relationship between fundamental forces by re-creating the earliest moments of the universe.

    Water Plays Unexpected Role in Forming Minerals

    Water molecules line up tiny particles to attach and form minerals; understanding how this happens impacts energy extraction and storage along with waste disposal.

    Heavy Particles Get Caught Up in the Flow

    First direct measurement show how heavy particles containing a charm quark get caught up in the flow of early universe particle soup.

    Seeing Between the Atoms

    New detector enables electron microscope imaging at record-breaking resolution.

    Scaling Up Single-Crystal Graphene

    New method can make films of atomically thin carbon that are over a foot long.

    Discovered: Optimal Magnetic Fields Suppress Instabilities in Tokamak Plasmas

    U.S. and Korean scientists show how to find and use beneficial 3-D field perturbations to stabilize dangerous edge-localized modes in plasma.


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