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  • richardmitnick 2:18 pm on October 3, 2017 Permalink | Reply
    Tags: , Condensed Matter Physics, New faculty to advance quantum matter research, , ,   

    From P.I. : “New faculty to advance quantum matter research” 

    Perimeter Institute
    Perimeter Institute

    October 2, 2017
    Tenille Bonoguore

    1
    Beni Yoshida

    2
    Yin-Chen He

    3
    Timothy Hsieh

    The research pursued by three new Faculty members at Perimeter Institute will advance understanding in a highly promising field.

    Three exceptional young researchers are set to join the faculty of Perimeter Institute, where they will bring new expertise to efforts to better understand, and one day exploit, quantum effects and condensed matter.

    Beni Yoshida – a former Perimeter postdoctoral researcher and “It from Qubit” Simons Fellow – is already at Perimeter. He will be joined in spring 2018 by Timothy Hsieh, currently a Gordon and Betty Moore Fellow and associate specialist at the Kavli Institute for Theoretical Physics, and Yin-Chen He, a Gordon and Betty Moore Fellow at Harvard University.

    All three study various aspects of condensed matter, which is being widely pursued as a solution to many challenges, from computing limits to efficient energy transmission. Together, they will lead the Institute’s new Quantum Matter Initiative.

    Perimeter Director Neil Turok described the appointments as a coup for the Institute, providing a leap forward in condensed matter research, one of the fastest-growing areas of physics today.

    “Quantum materials are expected to enable entirely new technologies with a host of potential applications,” Turok said. “With three exceptional young theorists joining our faculty, each bringing complementary skills and insights, Perimeter is preparing to engage with and support these exciting developments.”

    Yoshida studied and worked at MIT, and Caltech before coming to Perimeter in 2015. A specialist in quantum information theory, condensed matter, and black holes, his current work focuses on topological orders and quantum chaos.

    For Yoshida, the transition from postdoctoral fellow to faculty member promises exciting potential not just for his research but also for future collaborations. His research lies between three fields – quantum information, condensed matter, and string theory – all of which are represented in Perimeter’s faculty.

    “This field is relatively young. There are many brilliant young researchers and it’s a very energetic field. I want to bring more of those young talents here,” Yoshida said.

    “Perimeter is very interdisciplinary. I can learn from people with diverse interests. Of course, I was very happy to do research as a postdoc, but now I have more opportunity to make contributions to both PI and also to science, by bringing very smart students and postdocs. That’s probably most exciting.”

    Hsieh studied physics and mathematics at Harvard before earning his PhD in physics from MIT in 2015. A prediction he co-authored in 2013 – that a material called tin-telluride is a topological crystalline insulator – was experimentally confirmed by multiple groups and has spawned significant theoretical and experimental interest in its phenomenology.

    Hsieh said he was looking forward to exploring quantum materials, entanglement, and dynamics in Perimeter’s interdisciplinary environment.

    Yin-Chen He is a condensed matter researcher interested in spin liquids, topological phases, and topological phase transitions. He received his PhD from Shanghai’s Fudan University in 2014, and prior to moving to Harvard in 2016, worked at the Max Planck Institute in Dresden.

    “PI and I share a mutual interest in doing original, path-breaking research rather than following the main trends of the field,” He said.

    “PI has highly interdisciplinary research fields in theoretical physics as well as very active research members, and I am very much looking forward to being part of it.”

    See the full article here .

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    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

     
  • richardmitnick 9:46 am on September 28, 2017 Permalink | Reply
    Tags: , Condensed Matter Physics, , , , , Technical University of Dresden, The spin Hall effect, The spin Nernst effect, The spin Peltier effect, The spin Seebeck effect, Turning up the heat on electrons reveals an elusive physics phenomenon, When things heat up spinning electrons go their separate ways   

    From ScienceNews: “Turning up the heat on electrons reveals an elusive physics phenomenon” 

    ScienceNews bloc

    ScienceNews

    September 26, 2017
    Emily Conover

    Spin Nernst effect could help scientists design new gadgets that store data using quantum property of spin.

    1
    WHIRL AWAY Electrons in platinum move in different directions depending on their spin when the metal is heated at one end. Scientists have observed this phenomenon, called the spin Nernst effect, for the first time. Creativity103/Flickr (CC BY 2.0)

    When things heat up, spinning electrons go their separate ways.

    Warming one end of a strip of platinum shuttles electrons around according to their spin, a quantum property that makes them behave as if they are twirling around. Known as the spin Nernst effect, the newly detected phenomenon was the only one in a cadre of related spin effects that hadn’t previously been spotted, researchers report online September 11 in Nature Materials.

    “The last missing piece in the puzzle was spin Nernst and that’s why we set out to search for this,” says study coauthor Sebastian Goennenwein, a physicist at the Technical University of Dresden in Germany.

    The effect and its brethren — with names like the spin Hall effect, the spin Seebeck effect and the spin Peltier effect — allow scientists to create flows of electron spins, or spin currents. Such research could lead to smaller and more efficient electronic gadgets that use electrons’ spins to store and transmit information instead of electric charge, a technique known as “spintronics.”

    In the spin Nernst effect, named after Nobel laureate chemist Walther Nernst, heating one end of a metal causes electrons to flow toward the other end, bouncing around inside the material as they go. Within certain materials, that bouncing has a preferred direction: Electrons with spins pointing up (as if twirling counterclockwise) go to the right and electrons with spins pointing down (as if twirling clockwise) go to the left, creating an overall spin current. Although the effect had been predicted, no one had yet observed it.

    Finding evidence of the effect required disentangling it from other heat- and charge-related effects that occur in materials. To do so, the researchers coupled the platinum to a layer of a magnetic insulator, a material known as yttrium iron garnet. Then, they altered the direction of the insulator’s magnetization, which changed whether the spin current could flow through the insulator. That change slightly altered a voltage measured along the strip of platinum. The scientists measured how this voltage changed with the direction of the magnetization to isolate the fingerprints of the spin Nernst effect.

    “The measurement was a tour de force; the measurement was ridiculously hard,” says physicist Joseph Heremans of Ohio State University in Columbus, who was not involved with the research. The effect could help scientists to better understand materials that may be useful for building spintronic devices, he says. “It’s really a new set of eyes on the physics of what’s going on inside these devices.”

    A relative of the spin Nernst effect called the spin Hall effect is much studied for its potential use in spintronic devices. In the spin Hall effect, an electric field pushes electrons through a material, and the particles veer off to the left and right depending on their spin. The spin Nernst effect relies on the same basic physics, but uses heat instead of an electric field to get the particles moving.

    “It’s a beautiful experiment. It shows very nicely the spin Nernst effect,” says physicist Greg Fuchs of Cornell University. “It beautifully unifies our understanding of the interrelation between charge, heat and spin transport.”

    See the full article here .

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  • richardmitnick 7:35 am on September 1, 2017 Permalink | Reply
    Tags: , , Condensed Matter Physics, , MEC- Matter in Extreme Conditions, , , ,   

    From SLAC: “Newly Upgraded Laser Allows Scientists to Peer Further Into the Extreme Universe at SLAC’s LCLS” 


    SLAC Lab

    August 15, 2017
    Miyuki Dougherty

    1
    Highly reflective mirrors and telescope lenses in the Matter in Extreme Conditions (MEC) optical laser system are carefully positioned to propagate the instrument’s high-quality laser beams. The laser beams create extreme pressure and temperature conditions in materials that are instantaneously probed using hard X-rays from SLAC’s Linac Coherent Light Source (LCLS). (Dawn Harmer/SLAC National Accelerator Laboratory)

    Tripling the energy and refining the shape of optical laser pulses at the Matter in Extreme Conditions instrument allows researchers to create higher-pressure conditions and explore unsolved fusion energy, plasma physics and materials science questions.

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory recently upgraded a powerful optical laser system used to create shockwaves that generate high-pressure conditions like those found within planetary interiors. The laser system now delivers three times more energy for experiments with SLAC’s ultrabright X-ray laser, providing a more powerful tool for probing extreme states of matter in our universe.

    Together, the optical and X-ray lasers form the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS).

    SLAC/LCLS

    The high-power optical laser system creates extreme temperature and pressure conditions in materials, and the X-ray laser beam captures the material’s response.

    With this technology, researchers have already examined how meteor impacts shock minerals in the Earth’s crust and simulated conditions in Jupiter’s interior by turning aluminum foil into a warm, dense plasma.

    Higher Intensity and More Controlled Pulse Shapes

    The MEC instrument team received funding from the Office of Fusion Energy Sciences (FES) within the DOE’s Office of Science to double the amount of energy the optical beam can deliver in 10 nanoseconds, from 20 to 40 joules.

    But they went even further.

    “The team exceeded our expectations, an exciting accomplishment for the DOE High Energy Density program and future MEC instrument users,” says Kramer Akli, program manager for High Energy Density Laboratory Plasma at FES.

    The team tripled the amount of energy the laser can deliver in 10 nanoseconds to a spot on a target no bigger than the width of a few human hairs. When focused down to that small area, the laser provides users with intensities up to 75 terawatts per square centimeter.

    “In other terms, the upgraded laser has the same power as 17 Teslas discharging their 100 kilowatt-hour batteries in one second,” says Eric Galtier, a MEC instrument scientist.

    A portion of the energy upgrade can be attributed to the optical laser’s new, homemade diode pumped front-end, designed with the help of Marc Welch, a MEC laser engineer. The scientists also built and automated a system for shaping the laser pulses with extraordinary precision, allowing users substantially greater flexibility and control over the pulse shapes used in their experiments.

    A more powerful and reliable laser means that researchers can study higher pressure regimes and reach conditions relevant to fusion energy studies.

    Simulating the Core of Planets

    The MEC upgrade is promising for many researchers, including Shaughnessy Brennan Brown, a doctoral student in Mechanical Engineering, whose research focuses on high energy density science, which spans chemistry, materials science, and physics. Brennan Brown uses the MEC experimental hutch to drive shock waves through silicon and generate high-pressure conditions that occur in the Earth’s interior.

    “The MEC upgrade at LCLS enables researchers like me to generate exciting, previously-unexplored regimes of exotic matter – such as those found on Mars, our next planetary stepping stone – with crucial reliability and repeatability,” Brennan Brown says.

    Brennan Brown’s research examines the processes by which silicon in Earth’s core rearranges atomically under high temperature and pressure conditions. The thermodynamic properties of these high-pressure states affect our magnetic field, which protects us from the solar wind and allows us to survive on Earth. The laser upgrade will permit Brennan Brown to reach higher pressure and temperature conditions inside her samples, a long-standing goal.

    2
    Inside the MEC vacuum target chamber where researchers create transient states of matter using high-power optical lasers, which are then examined with SLAC’s Linac Coherent Light Source (LCLS) X-rays. (Matt Beardsley/SLAC National Accelerator Laboratory)

    Intensity Plus Precision

    The optical laser amplifies a low-power beam in stages and reaches increasingly high energies. However, the quality of the laser beam and ability to control it diminish during amplification. A low-quality pulse may start and end with a significantly different shape, which is not useful for researchers trying to recreate specific conditions.

    “The initial low energy pulse must have a pristine spatial mode and the properly configured temporal shape – that is, a precise sculpting of the pulse’s power as a function of time – before amplification to produce the laser pulse characteristics needed to enable each users’ experiment,” says Michael Greenberg, the MEC Laser Area Manager.

    Each target is unique and requires a specific energy and pulse shape, making manual tests and adjustments time-consuming. Prior to the upgrade, the team optimized the pulse shape by hand, taking anywhere from a few hours to a few days to properly calibrate it.

    To resolve this issue, Eric Cunningham, a laser scientist at MEC, developed an automated control system to shape the low-powered beam before amplification.

    3
    To demonstrate the MEC laser system’s enhanced ability to tailor the shape of laser pulses, scientists generated pulse shapes that spell out “M-E-C” in a plot of laser intensity vs. time. (Eric Cunningham and Michael Greenberg/SLAC National Accelerator Laboratory)

    “The new system allows for precise tailoring of the pulse shape using a computerized feedback loop system that analyzes the pulses and automatically re-calibrates the laser,” Cunningham said. The new optimizer is a promising system for generating many high-quality pulses in the most accurate and timely manner possible.

    In addition to the improved pulse shapes, the upgraded system deposits energy on samples more consistently from shot to shot, which allows researchers to very closely reproduce extreme states of matter in their samples. As a result, both the data quality and operational efficiency are improved.

    Brennan Brown says it’s the people and technology that make the instrument so successful: “The capability and competency of the laser scientists and engineers at the MEC experimental station offer researchers the technological resources they need to explore unanswered questions of the universe and bring their theories to life.”

    LCLS is a DOE Office of Science User Facility.

    See the full article here .

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 3:53 pm on July 26, 2017 Permalink | Reply
    Tags: , Condensed Matter Physics, Strange Electrons Break the Crystal Symmetry of High-Temperature Superconductors, Symmetry-breaking flow of electrons through copper-oxide, The symmetry-breaking voltage persisted up to room temperature and across the whole range of chemical compositions the scientists examined   

    From BNL: “Strange Electrons Break the Crystal Symmetry of High-Temperature Superconductors” 

    Brookhaven Lab

    July 26, 2017
    Justin Eure
    jeure@bnl.gov
    (631) 344-2347

    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    Brookhaven Lab scientists discover spontaneous voltage perpendicular to applied current that may help unravel the mystery of high-temperature superconductors.

    1
    Brookhaven Lab scientists (from left) Ivan Bozovic, Xi He, Jie Wu, and Anthony Bollinger with the atomic layer-by-layer molecular beam epitaxy system used to synthesize the superconducting cuprate samples.

    The perfect performance of superconductors could revolutionize everything from grid-scale power infrastructure to consumer electronics, if only they could be coerced into operating above frigid temperatures. Even so-called high-temperature superconductors (HTS) must be chilled to hundreds of degrees Fahrenheit below zero.

    Now, scientists from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Yale University have discovered new, surprising behavior by electrons in a HTS material. The results, published July 27 in the journal Nature, describe the symmetry-breaking flow of electrons through copper-oxide (cuprate) superconductors. The behavior may be linked to the ever-elusive mechanism behind HTS.

    “Our discovery challenges a cornerstone of condensed matter physics,” said lead author and Brookhaven Lab physicist Jie Wu. “These electrons seem to spontaneously ‘choose’ their own paths through the material — a phenomenon in direct opposition to expectations.”

    Off-road electrons

    In simple metals, electrons move evenly and without directional preference — think of a liquid spreading out on a surface. The HTS materials in this study are layered with four-fold rotational symmetry of the crystal structure. Electric current is expected to flow uniformly parallel to these layers — but this is not what the Brookhaven group observed.

    “I’m from the Midwest, where miles of farmland separate the cities,” said Brookhaven physicist and study coauthor Anthony Bollinger. “The country roads between the cities are largely laid out like a grid going north-to-south and east-to-west. You expect cars to follow the grid, which is tailor-made for them. This symmetry breaking is as if everyone decided to leave the paved roads and drive straight across farmers’ fields.”

    In another twist, the symmetry-breaking voltage persisted up to room temperature and across the whole range of chemical compositions the scientists examined.

    “The electrons somehow coordinate their movement through the material, even after the superconductivity fails,” said Wu.

    Strong electron-electron interactions may help explain the preferential direction of current flow. In turn, these intrinsic electronic quirks may share a relationship with HTS phenomena and offer a hint to decoding its unknown mechanism.

    Seeking atomic perfection

    Unlike well-understood classical superconductivity, HTS has puzzled scientists for more than three decades. Now, advanced techniques are offering unprecedented insights.

    “The most difficult part of the whole work — and what helps set us apart — was the meticulous material synthesis,” said study coauthor Xi He.

    This work was a part of a larger project that took 12 years and encompassed the synthesis and study of more than 2,000 films of lanthanum-strontium-copper-oxide superconductors.

    “This scale of research is well-suited to a national laboratory environment,” said Ivan Bozovic, who leads the Brookhaven group behind the effort.

    They use a technique called molecular beam epitaxy (MBE) to assemble complex oxides one atomic layer at a time. To ensure structural perfection, the scientists characterize the materials in real time with electron diffraction, where an electron beam strikes the sample and sensitive detectors measure precisely how it scatters.

    “The material itself is our foundation, and it must be as flawless as possible to guarantee that the observed properties are intrinsic,” Bozovic said. “Moreover, by virtue of our ‘digital’ synthesis, we engineer the films at the atomic-layer level, and optimize them for different studies.”

    Swimming against the current

    The first major result of this comprehensive study by the MBE group at Brookhaven was published in Nature last year. It demonstrated that the superconducting state in copper-oxide materials is quite unusual, challenging the standard understanding.

    That finding suggested that the so-called “normal” metallic state, which forms above the critical temperature threshold at which superconductivity breaks down, might also be extraordinary. Looking carefully, the scientists observed that as external current flowed through the samples, a spontaneous voltage unexpectedly emerged perpendicular to that current.

    “We first observed this bizarre voltage over a decade ago, but we and others discounted that as some kind of error,” Bollinger said. “But then it showed up again, and again, and again — under increasingly controlled conditions — and we ran out of ways to explain it away. When we finally dove in, the results exceeded our expectations.”

    To pin down the origin of the phenomenon, the scientists fabricated and measured thousands of devices patterned out of the HTS films. They studied how this spontaneous voltage depends on the current direction, temperature, and the chemical composition (the level of doping by strontium, which controls the electron density). They also varied the type and the crystal structure of the substrates on which the HTS films are grown, and even how the substrates are polished.

    These meticulous studies showed beyond doubt that the effect is intrinsic to the HTS material itself, and that its origin is purely electronic.

    At the molecular level, common liquids look the same in every direction. Some, however, are comprised of rod-like molecules, which tend to align in one preferred direction. Such materials are called liquid crystals — they polarize light and are widely used in displays. While electrons in common metals behave as a liquid, in cuprates they behave as an electronic liquid crystal.

    “We need to understand how this electron behavior fits into the HTS puzzle as a whole,” He said. “This study gives us new ideas to pursue and ways to tackle what may be the biggest mystery in condensed matter physics. I’m excited to see where this research takes us.”

    Authors Bozovic and He share affiliation with Brookhaven Lab and Yale University.

    The research was funded by DOE’s Office of Science.

    See the full article here .

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 6:36 am on June 15, 2017 Permalink | Reply
    Tags: , , Condensed Matter Physics, , , , RIXS, ,   

    From SLAC: “New Research Finds a Missing Piece to High-Temperature Superconductor Mystery” 


    SLAC Lab

    June 14, 2017
    Mike Ross

    1
    This sketch shows how resonant inelastic X-ray scattering (RIXS) helps scientists understand the electronic behavior of copper oxide materials. An X-ray photon aimed at the sample (blue arrow) is absorbed by a copper atom, which then emits a new, lower-energy photon (red arrow) as it relaxes. The amount of momentum transferred and energy lost in this process can induce changes in the charge density waves thought to be important in high-temperature superconductivity. (Wei-Sheng/SLAC National Accelerator Laboratory)

    An international team led by scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University has detected new features in the electronic behavior of a copper oxide material that may help explain why it becomes a perfect electrical conductor – a superconductor – at relatively high temperatures.

    Using an ultrahigh-resolution X-ray instrument in France, the researchers for the first time saw dynamic behaviors in the material’s charge density wave (CDW) – a pattern of electrons that resembles a standing wave – that lend support to the idea that these waves may play a role in high-temperature superconductivity.

    Data taken at low (20 kelvins) and high (240 kelvins) temperatures showed that as the temperature increased, the CDW became more aligned with the material’s atomic structure. Remarkably, at the lower temperature, the CDW also induced an unusual increase in the intensity of the oxide’s atomic lattice vibrations, indicating that the dynamic CDW behaviors can propagate through the lattice.

    “Previous research has shown that when the CDW is static, it competes with and diminishes superconductivity,” said co-author Wei-Sheng Lee, a SLAC staff scientist and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES), which led the study published June 12 in Nature Physics. “If, on the other hand, the CDW is not static but fluctuating, theory tells us they may actually help form superconductivity.”

    A Decades-long Search for an Explanation

    The new result is the latest in a decades-long search by researchers worldwide for the factors that enable certain materials to become superconducting at relatively high temperatures.

    Since the 1950s, scientists have known how certain metals and simple alloys become superconducting when chilled to within a few degrees of absolute zero: Their electrons pair up and ride waves of atomic vibrations that act like a virtual glue to hold the pairs together. Above a certain temperature, however, the glue fails as thermal vibrations increase, the electron pairs split up and superconductivity disappears.

    In 1986, complex copper oxide materials were found to become superconducting at much higher – although still quite cold – temperatures. This discovery was so unexpected it caused a worldwide scientific sensation. By understanding and optimizing how these materials work, researchers hope to develop superconductors that work at room temperature and above.

    At first, the most likely glue holding superconducting electron pairs together at higher temperatures seemed to be strong magnetic excitations created by interactions between electron spins. But in 2014, a theoretical simulation and experiments led by SIMES researchers concluded that these high-energy magnetic interactions are not the sole factor in copper oxide’s high-temperature superconductivity. An unanticipated CDW also appeared to be important.

    The latest results continue the SIMES collaboration between experiment and theory. Building upon previous theories of how electron interactions with lattice vibrations can be probed with resonant inelastic X-ray scattering, or RIXS, the signature of CDW dynamics was finally identified, providing additional support for the CDW’s role in determining the electronic structure in superconducting copper oxides.

    The Essential New Tool: RIXS

    The new results are enabled by the development of more capable instruments employing RIXS. Now available at ultrahigh resolution at the European Synchrotron Radiation Facility (ESRF) in France, where the team performed this experiment, RIXS will also be an important feature of SLAC’s upgraded Linac Coherent Light Source X-ray free-electron laser, LCLS-II.


    ESRF. Grenoble, France

    SLAC LCLS-II

    The combination of ultrahigh energy resolution and a high pulse repetition rate at LCLS-II will enable researchers to see more detailed CDW fluctuations and perform experiments aimed at revealing additional details of its behavior and links to high-temperature superconductivity. Most importantly, researchers at LCLS-II will be able to use ultrafast light-matter interactions to control CDW fluctuations and then take femtosecond-timescale snapshots of them.

    RIXS involves illuminating a sample with X-rays that have just enough energy to excite some electrons deep inside the target atoms to jump up into a specific higher orbit. When the electrons relax back down into their previous positions, a tiny fraction of them emit X-rays that carry valuable atomic-scale information about the material’s electronic and magnetic configuration that is thought to be important in high-temperature superconductivity.

    “To date, no other technique has seen evidence of propagating CDW dynamics,” Lee said.

    RIXS was first demonstrated in the mid-1970s [Physical Review Letters], but it could not obtain useful information to address key problems until 2007, when Giacomo Ghiringhelli, Lucio Braicovich at Milan Polytechnic in Italy and colleagues at Swiss Light Source made a fundamental change that improved its energy resolution to a level where significant details became visible – technically speaking to about 120 milli-electronvolts (meV) at the relevant X-ray wavelength, which is called a copper L edge. The new RIXS instrument at ESRF is three times better, routinely attaining an energy resolution down to 40 meV. Since 2014, the Milan group has collaborated with SLAC and Stanford scientists in their RIXS research.

    “The new ultrahigh resolution RIXS makes a huge difference,” Lee said. “It can show us previously invisible details.”

    Other researchers involved in this result were from Milan Polytechnic, European Synchrotron Radiation Facility, Japan’s National Institute of Advanced Industrial Science and Technology and Italy’s National Research Council Institute for Superconductors, Oxides and Other Innovative Materials and Devices (CNR-SPIN). Funding for this research came from the DOE Office of Science.

    See the full article here .

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    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 11:55 am on June 11, 2017 Permalink | Reply
    Tags: Condensed Matter Physics, Dr. Binghai Yan, , Topological materials,   

    From Weizmann: “Physics on the edge” 

    Weizmann Institute of Science logo

    Weizmann Institute of Science

    1
    Dr. Binghai Yan

    Dr. Binghai Yan is taking topological materials higher.

    Creating new materials for everyday life—think bendable electronics, quantum computers, life-saving medical devices and things we haven’t yet dreamed of—requires understanding and creatively brainstorming new possibilities at the atomic level.

    This is the essence Dr. Binghai Yan’s research. His field is topological materials, which is fusing theoretical science with practical engineering and taking the physics world by storm. And yes, his name gives away the other special news: he is the first principal investigator from China hired by the Weizmann Institute.

    Topological materials and states involve a kind of order very different from conventional bulk materials in that electrons (and their lattices of atoms and molecules) on the surface of a crystal or other material behave differently than those in the material itself. In is the special nature of such topological materials and states that can be leveraged for the creation of new materials. He straddles the world of theory—how such states could work—and experimentation—trying out the materials to synthesize new materials and devices such as quantum computers.

    From rural fields to topology

    So how did a Chinese physicist who grew up in a remote farming village in Shandong Province in eastern China make his way to the Weizmann Institute?

    After completing his BSc at Xi’an Jiatong University in Xi’an in 2003, he earned a PhD in physics at the Tsinghua University in Beijing in 2008. He did postdoctoral research at the University of Bremen in Germany, when the field of topological research was beginning to take off. But it was still a relatively niche subject in which few physicists were working. Thanks to a flexible postdoc grant, the prestigious Humboldt Research Fellowship, which allowed him to spend time at other institutions, he spent eight months at Stanford University learning from a leading expert in the field.

    He returned to Germany to become a group leader (the equivalent of a principal investigator) at the Max Planck Institute for Chemical Physics and Solids in Dresden. It was then that he began collaborating with Weizmann Institute colleagues—thanks to an introduction by Prof. Ady Stern at a conference in Germany—including Prof. Erez Berg and Dr. Haim Beidenkopf, all from the Department of Condensed Matter Physics. The collaboration was enabled by an ARCHES Award given by Germany’s Minerva Foundation, which stimulates collaborative projects by German and Israeli scientists. He visited the Weizmann Institute for the first time in 2013 to advance this work.

    The project and the visit were a “fantastic opportunity,” he says, because his Weizmann collaborators were both theoreticians and experimentalists who were eager to learn about the material he was working on—and Dr. Yan needed feedback from theory to advance his investigations by predicting possible new materials and actualize his ideas in experiments. “I immediately realized that we have lots to do,” he says. “Together, we are able to bridge fundamental physics and experimentation.”

    Last year, he received a competing offer from a university in China, but took the Weizmann offer “because of my existing collaborations and potential collaborations, the depth of theory and experiment work here, and the fact that Weizmann is one of the few places that is advancing this field,” he says.

    Dr. Yan has already discovered a new class of topological materials: a three-dimensional, layered, metallic insulating material which he grows in the lab. He has done so by way of his expertise in electron charge and spin, and so this research has implications for the new, hot field of “spintronics”. Spintronics differs from traditional electronics in that it leverages the way in which electrons spin—not only their charge—to find better efficiency with data storage and transfer. This, in turn, has relevance for the new age of quantum computing, and he hopes to collaborate with quantum computing pioneers at the Institute.

    For his wife, Huanhuan Wang, the decision to make a potentially permanent move to Israel—a country she’d never before visited and about which she had little knowledge—was not as obvious as it was for Dr. Yan. “It took a little bit of convincing my wife to come; if you’ve never been here, all you think is political strife,” says Dr. Yan. “But the reality is different. We are really happy here and it is quickly starting to feel like home.”

    The family arrived in February and moved into campus housing. His wife is now pursuing a PhD under the guidance of Prof. Dan Yakir in the Department of Plant and Environmental Sciences. They have two kids, a boy and a girl, who just began learning German, and now are getting used to Hebrew—and they speak Chinese at home.

    Dr. Yan is finding opportunities to collaborate with scientists in Germany and China, and has already begun organizing a workshop on topological systems at the Weizmann Institute (together with Dr. Haim Beidenkopf and Dr. Nurit Avraham, also of the Department of Physics of Condensed Matter Physics), to which he has invited leading European and Chinese physicists and other leaders in the field.

    “Being in Israel, at Weizmann, is not something that I would have anticipated five or 10 years ago,” he says. “But life—like the materials of the future—holds many mysteries.”

    Dr. Yan is supported by the Ruth and Herman Albert Scholars Program for New Scientists.

    See the full article here .

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    Weizmann Institute Campus

    The Weizmann Institute of Science is one of the world’s leading multidisciplinary research institutions. Hundreds of scientists, laboratory technicians and research students working on its lushly landscaped campus embark daily on fascinating journeys into the unknown, seeking to improve our understanding of nature and our place within it.

    Guiding these scientists is the spirit of inquiry so characteristic of the human race. It is this spirit that propelled humans upward along the evolutionary ladder, helping them reach their utmost heights. It prompted humankind to pursue agriculture, learn to build lodgings, invent writing, harness electricity to power emerging technologies, observe distant galaxies, design drugs to combat various diseases, develop new materials and decipher the genetic code embedded in all the plants and animals on Earth.

    The quest to maintain this increasing momentum compels Weizmann Institute scientists to seek out places that have not yet been reached by the human mind. What awaits us in these places? No one has the answer to this question. But one thing is certain – the journey fired by curiosity will lead onward to a better future.

     
  • richardmitnick 3:59 pm on April 13, 2016 Permalink | Reply
    Tags: , , Condensed Matter Physics,   

    From Princeton: “Electrons slide through the hourglass on surface of bizarre material (Nature)” 

    Princeton University
    Princeton University

    April 13, 2016
    By Staff

    1
    An illustration of the hourglass fermion predicted to lie on the surface of crystals of potassium mercury antimony. (Image credit: Laura R. Park and Aris Alexandradinata)

    A team of researchers at Princeton University has predicted the existence of a new state of matter in which current flows only through a set of surface channels that resemble an hourglass. These channels are created through the action of a newly theorized particle, dubbed the “hourglass fermion,” which arises due to a special property of the material. The tuning of this property can sequentially create and destroy the hourglass fermions, suggesting a range of potential applications such as efficient transistor switching.

    In an article published in the journal Nature* this week, the researchers theorize the existence of these hourglass fermions in crystals made of potassium and mercury combined with either antimony, arsenic or bismuth. The crystals are insulators in their interiors and on their top and bottom surfaces, but perfect conductors on two of their sides where the fermions create hourglass-shaped channels that enable electrons to flow.

    The research was performed by Princeton University postdoctoral researcher Zhi Jun Wang and former graduate student Aris Alexandradinata, now a postdoctoral researcher at Yale University, working with Robert Cava, Princeton’s Russell Wellman Moore Professor of Chemistry, and Associate Professor of Physics B. Andrei Bernevig.

    The new hourglass fermion exists – theoretically for now, until detected experimentally – in a family of materials broadly called topological insulators, which were first observed experimentally in the mid-2000s and have since become one of the most active and interesting branches of quantum physics research. The bulk, or interior, acts as an insulator, which means it prohibits the travel of electrons, but the surface of the material is conducting, allowing electrons to travel through a set of channels created by particles known as Dirac fermions.

    Fermions are a family of subatomic particles that include electrons, protons and neutrons, but they also appear in nature in many lesser known forms such as the massless Dirac, Majorana and Weyl fermions. After years of searching for these particles in high-energy accelerators and other large-scale experiments, researchers found that they can detect these elusive fermions in table-top laboratory experiments on crystals. Over the past few years, researchers have used these “condensed matter” systems to first predict and then confirm the existence of Majorana and Weyl fermions in a wide array of materials.

    The next frontier in condensed matter physics is the discovery of particles that can exist in the so-called “material universe” inside crystals but not in the universe at large. Such particles come about due to the properties of the materials but cannot exist outside the crystal the way other subatomic particles do. Classifying and discovering all the possible particles that can exist in the material universe is just beginning. The work reported by the Princeton team lays the foundations of one of the most interesting of these systems, according to the researchers.

    In the current study, the researchers theorize that the laws of physics prohibit current from flowing in the crystal’s bulk and top and bottom surfaces, but permit electron flow in completely different ways on the side surfaces through the hourglass-shaped channels. This type of channel, known more precisely as a dispersion, was completely unknown before.

    The researchers then asked whether this dispersion is a generic feature found in certain materials or just a fluke arising from a specific crystal model.

    It turned out to be no fluke.

    A long-standing collaboration with Cava, a material science expert, enabled Bernevig, Wang, and Alexandradinata to uncover more materials exhibiting this remarkable behavior.

    “Our hourglass fermion is curiously movable but unremovable,” said Bernevig. “It is impossible to remove the hourglass channel from the surface of the crystal.”

    Bernevig explained that this robust property arises from the intertwining of spatial symmetries, which are characteristics of the crystal structure, with the modern band theory of crystals. Spatial symmetries in crystals are distinguished by whether a crystal can be rotated or otherwise moved without altering its basic character.

    In a paper published in Physical Review X** this week to coincide with the Nature paper, the team detailed the theory behind how the crystal structure leads to the existence of the hourglass fermion.

    2
    An illustration of the complicated dispersion of the surface fermion arising from a background of mercury and bismuth atoms (blue and red). (Image credit: Mingyee Tsang and Aris Alexandradinata)

    “Our work demonstrates how this basic geometric property gives rise to a new topology in band insulators,” Alexandradinata said. The hourglass is a robust consequence of spatial symmetries that translate the origin by a fraction of the lattice period, he explained. “Surface bands connect one hourglass to the next in an unbreakable zigzag pattern,” he said.

    The team found esoteric connections between their system and high-level mathematics. Origin-translating symmetries, also called non-symmorphic symmetries, are described by a field of mathematics called cohomology, which classifies all the possible crystal symmetries in nature. For example, cohomology gives the answer to how many crystal types exist in three spatial dimensions: 230.

    In the cohomological perspective, there are 230 ways to combine origin-preserving symmetries with real-space translations, known as the “space groups.” The theoretical framework to understand the crystals in the current study requires a cohomological description with momentum-space translations.

    “The hourglass theory is the first of its kind that describes time-reversal-symmetric crystals, and moreover, the crystals in our study are the first topological material class which relies on origin-translating symmetries,” added Wang.

    Out of the 230 space groups in which materials can exist in nature, 157 are non-symmorphic, meaning they can potentially host interesting electronic behavior such as the hourglass fermion.

    “The exploration of the behavior of these interesting fermions, their mathematical description, and the materials where they can be observed, is poised to create an onslaught of activity in quantum, solid state and material physics,” Cava said. “We are just at the beginning.”

    The study was funded by the National Science Foundation, the Office of Naval Research, the David and Lucile Packard Foundation, the W. M. Keck Foundation, and the Eric and Wendy Schmidt Transformative Technology Fund at Princeton University.

    Read the abstract or preprint.

    *Science paper
    Hourglass fermions

    Science team:
    Zhijun Wang, A. Alexandradinata, R. J. Cava & B. Andrei Bernevig

    Affiliations

    Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
    Zhijun Wang, A. Alexandradinata & B. Andrei Bernevig
    Department of Physics, Yale University, New Haven, Connecticut 06520, USA
    A. Alexandradinata
    Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
    R. J. Cava

    Contributions

    A.A., Z.W. and B.A.B. performed theoretical analysis; Z.W. discovered the KHgX material class and performed the first-principles calculations; R.J.C. provided several other material suggestions.

    ** Not made available

    See the full article here .

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    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 4:24 pm on December 19, 2014 Permalink | Reply
    Tags: , Condensed Matter Physics, , , ,   

    From SLAC: “First Direct Evidence that a Mysterious Phase of Matter Competes with High-Temperature Superconductivity” 


    SLAC Lab

    December 19, 2014

    SLAC Study Shows “Pseudogap” Phase Hoards Electrons that Might Otherwise Conduct Electricity with 100 Percent Efficiency

    Scientists have found the first direct evidence that a mysterious phase of matter known as the “pseudogap” competes with high-temperature superconductivity, robbing it of electrons that otherwise might pair up to carry current through a material with 100 percent efficiency.

    The result, led by researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory, is the culmination of 20 years of research aimed at finding out whether the pseudogap helps or hinders superconductivity, which could transform society by making electrical transmission, computing and other areas much more energy efficient.

    2
    This illustration shows the complex relationship between high-temperature superconductivity (SC) and a mysterious phase called the pseudogap (PG). Copper oxide materials become superconducting when an optimal number of electrons are removed, leaving positively charged “holes,” and the material is chilled below a transition temperature (blue curve). This causes remaining electrons (yellow) to pair up and conduct electricity with 100 percent efficiency. Experiments at SLAC have produced the first direct evidence that the pseudogap competes for electrons with superconductivity over a wide range of temperatures at lower hole concentrations (SC+PG). At lower temperatures and higher hole concentrations, superconductivity wins out. (SLAC National Accelerator Laboratory)

    The new study definitively shows that the pseudogap is one of the things that stands in the way of getting superconductors to work at higher temperatures for everyday uses, said lead author Makoto Hashimoto, a staff scientist at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), the DOE Office of Science User Facility where the experiments were carried out. The results were published in Nature Materials.

    SLAC SSRL
    SSRL

    “Now we have clear, smoking-gun evidence that the pseudogap phase competes with and suppresses superconductivity,” Hashimoto said. “If we can somehow remove this competition, or handle it better, we may be able to raise the operating temperatures of these superconductors.”

    Tracking Down Electrons

    In the experiments, researchers used a technique called angle-resolved photoemission spectroscopy, or ARPES, to knock electrons out of a copper oxide material, one of a handful of materials that superconduct at relatively high temperatures – although they still have to be chilled to at least minus 135 degrees Celsius.

    Plotting the energies and momenta of the ejected electrons tells researchers how they were behaving when they were inside the material. In metals, for instance, electrons freely flow around and between atoms. In insulators, they stick close to their home atoms. And in superconductors, electrons leave their usual positions and pair up to conduct electricity with zero resistance and 100 percent efficiency; the missing electrons leave a characteristic gap in the researchers’ plots.

    But in the mid-1990s, scientists discovered another, puzzling gap in their plots of copper oxide superconductors. This “pseudogap” looked like the one left by superconducting electrons, but it showed up at temperatures too warm for superconductivity to occur. Was it a lead-in to superconducting behavior? A rival state that held superconductivity at bay? Where did it come from? No one knew.

    “It’s a complex, intimate relationship. These two phenomena likely share the same roots but are ultimately antagonistic,” said Zhi-Xun Shen, a professor at SLAC and Stanford and senior author of the study. “When the pseudogap is winning, superconductivity is losing ground.”

    Evidence of Competition

    Shen and his colleagues have been using ARPES to investigate the pseudogap ever since it showed up, refining their techniques over the years to pry more information out of the flying electrons.

    In this latest study, Hashimoto was able to find out exactly what was happening at the moment the material transitioned into a superconducting state. He did this by measuring not only the energies and momenta of the electrons, but the number of electrons coming out of the material with particular energies over a wide range of temperatures, and after the electronic properties of the material had been altered in various ways.

    He discovered clear, strong evidence that at this crucial transition temperature, the pseudogap and superconductivity are competing for electrons. Theoretical calculations by members of the team were able to reproduce this complex relationship.

    “The pseudogap tends to eat away the electrons that want to go into the superconducting state,” explained Thomas Devereaux, a professor at Stanford and SLAC and co-author of the study. “The electrons are busy doing the dance of the pseudogap, and superconductivity is trying to cut in, but the electrons are not letting that happen. Then, as the material goes into the superconducting state, the pseudogap gives up and spits the electrons back out. That’s really the strongest evidence we have that this competition is occurring.”

    Remaining Mysteries

    Scientists still don’t know what causes the pseudogap, Devereaux said: “This remains one of the most important questions in the field, because it’s clearly preventing superconductors from working at even higher temperatures, and we don’t know why.”

    But the results pave new directions for further research, the scientists said.

    “Now we can model the competition between the pseudogap and superconductivity from the theoretical side, which was not possible before,” Hashimoto said. “We can use simulations to reproduce the kinds of features we have seen, and change the variables within those simulations to try to pin down what the pseudogap is.”

    He added, “Competition may be only one aspect of the relationship between the two states. There may be more profound questions – for example, whether the pseudogap is necessary for superconductivity to occur.”

    In addition to SLAC and Stanford, researchers from Lawrence Berkeley National Laboratory, Osaka University, the National Institute of Advanced Industrial Science and Technology in Japan, the Japan Atomic Energy Agency, Tokyo Institute of Technology, University of Tokyo and Cornell University contributed to the study. The research was supported by the DOE Office of Science.

    See the full article here.

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    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 9:09 am on August 15, 2014 Permalink | Reply
    Tags: , Condensed Matter Physics,   

    From Brookhaven Lab: “New Grant to Aid Search for the Secrets of Superconductivity” 

    Brookhaven Lab

    August 12, 2014
    Karen McNulty Walsh

    Research aimed at unlocking the secrets of high-temperature superconductivity at the U.S. Department of Energy’s Brookhaven National Laboratory will get a boost from a new grant awarded to Ivan Bozovic, a Brookhaven physicist and an Adjunct Professor at Yale University, by the Gordon and Betty Moore Foundation. Bozovic will receive $1.9 million over five years as part of the Moore Materials Synthesis Investigators program to continue the meticulous assembly and manipulation of superconducting thin films and the exploration of factors underlying these remarkable materials’ ability to carry electric current with no energy loss.

    “I am very grateful for this grant, which recognizes the importance of methodical work that slowly but steadily improves materials synthesis techniques and sample quality,” Bozovic said. Such quality is essential to uncover subtle effects in high-temperature superconductors, which, Bozovic notes, can be masked by impurities. “The better the samples, the more precise and revealing our experiments can be — and the greater their potential for new insights and discoveries,” he said.

    To achieve such precision, Bozovic uses a one-of-a-kind molecular-beam epitaxy (MBE) machine that he built and continues to improve to fabricate superconducting thin films one atomic layer at a time. He and collaborators have used the machine to assemble more than 2,000 thin film samples and conduct hundreds of scientific experiments. He also contributes to research at Brookhaven’s Center for Emergent Superconductivity, one of DOE’s Energy Frontier Research Centers, which recently received renewed funding.

    “I am very grateful for this grant, which recognizes the importance of methodical work that slowly but steadily improves materials synthesis techniques and sample quality.”
    — Brookhaven physicist Ivan Bozovic

    ib

    Leveraging his atomic-layer-by-layer synthesis technique, Bozovic made a series of discoveries related to interface superconductivity, bringing it to the forefront of research in Condensed Matter Physics. He showed that superfluid can be confined to a single atomic layer at the interface of two materials, neither of which is superconducting. In another important experiment, he proved that electron pairs exist on both sides of the superconductor-to-insulator transition an important insight into the mysterious nature of the high-temperature superconductivity phenomenon.

    Bozovic is one of only 12 scientists to be awarded funding through the Moore Materials Synthesis Investigators program, part of the foundation’s Emerging Phenomena in Quantum Systems (EPiQS) initiative. Quantum materials, the Foundation notes, are substances in which the collective behavior of electrons leads to many complex and unexpected emergent phenomena, superconductivity being a prominent example.

    In announcing the grantees, the Foundation stated:

    “Our approach is to focus on some of the field’s leading scientists; to allow these scientists the freedom to explore and the flexibility to change research directions; and to incentivize sample sharing within the EPiQS program and beyond…We believe that our programs will lead to discoveries of new quantum materials with emergent electronic properties as well as an increase in the availability of top-quality samples to the experimental community.”

    Bozovic earned a Ph.D. in physics from the University of Belgrade in Yugoslavia in 1975. He remained there until 1985 and served as a professor and the Head of the Physics Department. From 1986 until 1988, he worked at the Applied Physics Department at Stanford University. He was a senior research scientist at Varian Research Center in Palo Alto, California, 1989 to 1998, and the chief technical officer and principal scientist for Oxxel GmbH in Germany 1998 to 2002. He joined Brookhaven as a senior scientist and the leader of the Molecular Beam Epitaxy group in 2003. In 2012 he was a co-recipient of the Bernd T. Matthias Prize for Superconducting Materials, and in 2013 was chosen to give the Max Planck Lecture at MPI-Stuttgart, Germany. His research results have been published in more than 200 research papers and cited more than 6,500 times. Many of these were published in the highest-impact journals such as Nature, Science, and Nature Materials. Bozovic is a Fellow of APS and of SPIE, and a Foreign Member of Serbian Academy of Science and Arts.

    Bozovic’s research at Brookhaven is supported by the DOE Office of Science. The Moore Foundation grant will be awarded to him by way of his adjunct appointment at Yale University.

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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