Tagged: Condensed Matter Physics Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 5:06 pm on February 13, 2020 Permalink | Reply
    Tags: "Study uncovers new electronic state of matter", Condensed Matter Physics, , , , We have moved into the era of research in quantum computing; quantum teleportation; quantum communications; and quantum sensing.   

    From University of Pittsburgh via phys.org: “Study uncovers new electronic state of matter” 

    U Pitt bloc

    From University of Pittsburgh

    via


    From phys.org

    2.13.20

    1
    Clumps of electrons speeding down the superconductor highway represent the the motion of the Pascal conductance series. Credit: Jeremy Levy

    A research team led by professors from the University of Pittsburgh Department of Physics and Astronomy has announced the discovery of a new electronic state of matter.

    Jeremy Levy, a distinguished professor of condensed matter physics, and Patrick Irvin, a research associate professor are coauthors of the paper Pascal conductance series in ballistic one-dimensional LaAIO3/SrTiO3 channels. The research focuses on measurements in one-dimensional conducting systems where electrons are found to travel without scattering in groups of two or more at a time, rather than individually.

    The study was published in Science on Feb. 14.

    “Normally, electrons in semiconductors or metals move and scatter, and eventually drift in one direction if you apply a voltage. But in ballistic conductors the electrons move more like cars on a highway. The advantage of that is they don’t give off heat and may be used in ways that are quite different from ordinary electronics. Researchers before us have succeeded in creating this kind of ballistic conductor,” explained Levy.

    “The discovery we made shows that when electrons can be made to attract one another, they can form bunches of two, three, four and five electrons that literally behave like new types of particles, new forms of electronic matter.”


    34:15
    11Levels: Pascal conductance series in ballistic one-dimensional LaAlO3/SrTiO3 channels

    Levy compared the finding to the way in which quarks bind together to form neutrons and protons. An important clue to uncovering the new matter was recognizing that these ballistic conductors matched a sequence within Pascal’s Triangle.

    “If you look along different directions of Pascal’s Triangle you can see different number patterns and one of the patterns was one, three, six, 10, 15, 21. This is a sequence we noticed in our data, so it became a challenging clue as to what was actually going on. The discovery took us some time to understand but it was because we initially did not realize we were looking at particles made up of one electron, two electrons, three electrons and so forth. If you combine all this together you get the sequence of 1,3,6,10.”

    Levy, who is also director of the Pittsburgh Quantum Institute, noted that the new particles feature properties related to quantum entanglement, which can potentially be used for quantum computing and quantum redistribution. He said the discovery is an exciting advancement toward the next stage of quantum physics.

    “This research falls within a larger effort here in Pittsburgh to develop new science and technologies related to the second quantum revolution,” he said.

    “In the first quantum revolution people discovered the world around them was governed fundamentally by laws of quantum physics. That discovery led to an understanding of the periodic table, how materials behave and helped in the development of transistors, computers, MRI scanners and information technology.

    “Now in the 21st century, we’re looking at all the strange predictions of quantum physics and turning them around and using them. When you talk about applications, we’re thinking about quantum computing, quantum teleportation, quantum communications, quantum sensing—ideas that use properties of the quantum nature of matter that were ignored before.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    About Science X in 100 words

    Science X™ is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004 (Physorg.com), Science X’s readership has grown steadily to include 5 million scientists, researchers, and engineers every month. Science X publishes approximately 200 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Science X community members enjoy access to many personalized features such as social networking, a personal home page set-up, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.
    Mission 12 reasons for reading daily news on Science X Organization Key editors and writersinclude 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

    U Pitt campus

    The University of Pittsburgh is a state-related research university, founded as the Pittsburgh Academy in 1787. Pitt is a member of the Association of American Universities (AAU), which comprises 62 preeminent doctorate-granting research institutions in North America.

    From research achievements to the quality of its academic programs, the University of Pittsburgh ranks among the best in higher education.

    Faculty members have expanded knowledge in the humanities and sciences, earning such prestigious honors as the National Medal of Science, the MacArthur Foundation’s “genius” grant, the Lasker-DeBakey Clinical Medical Research Award, and election to the National Academy of Sciences and the Institute of Medicine.

    Pitt students have earned Rhodes, Goldwater, Marshall, and Truman Scholarships, among other highly competitive national and international scholarships.

    Alumni have pioneered MRI and TV, won Nobels and Pulitzers, led corporations and universities, served in government and the military, conquered Hollywood and The New York Times bestsellers list, and won Super Bowls and NBA championships.

     
  • richardmitnick 12:40 pm on February 7, 2020 Permalink | Reply
    Tags: "Making High-Temperature Superconductivity Disappear to Understand Its Origin", (SI-STM)-spectroscopic imaging–scanning tunneling microscopy, , , , Condensed Matter Physics, , , , OASIS- a new on-site experimental machine for growing and characterizing oxide thin films., ,   

    From Brookhaven National Lab: “Making High-Temperature Superconductivity Disappear to Understand Its Origin” 

    From Brookhaven National Lab

    February 3, 2020
    Ariana Manglaviti
    amanglaviti@bnl.gov
    (631) 344-2347

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

    Scientists have collected evidence suggesting that a purely electronic mechanism causes copper-oxygen compounds to conduct electricity without resistance at temperatures well above absolute zero.

    1
    Brookhaven Lab physicists (from left to right) Genda Gu, Tonica Valla, and Ilya Drozdov at OASIS, a new on-site experimental machine for growing and characterizing oxide thin films, such as those of a class of high-temperature superconductors (HTS) known as the cuprates. Compared to conventional superconductors, HTS become able to conduct electricity without resistance at much warmer temperatures. The team used the unique capabilities at OASIS to make superconductivity in a cuprate sample disappear and then reappear in order to understand the origin of the phenomenon.

    When there are several processes going on at once, establishing cause-and-effect relationships is difficult. This scenario holds true for a class of high-temperature superconductors known as the cuprates. Discovered nearly 35 years ago, these copper-oxygen compounds can conduct electricity without resistance under certain conditions. They must be chemically modified (“doped”) with additional atoms that introduce electrons or holes (electron vacancies) into the copper-oxide layers and cooled to temperatures below 100 Kelvin (−280 degrees Fahrenheit)—significantly warmer temperatures than those needed for conventional superconductors. But exactly how electrons overcome their mutual repulsion and pair up to flow freely in these materials remains one of the biggest questions in condensed matter physics. High-temperature superconductivity (HTS) is among many phenomena occurring due to strong interactions between electrons, making it difficult to determine where it comes from.

    That’s why physicists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory studying a well-known cuprate containing layers made of bismuth oxide, strontium oxide, calcium, and copper oxide (BSCCO) decided to focus on the less complicated “overdoped” side, doping the material so much so that superconductivity eventually disappears. As they reported in a paper published on Jan. 29 in Nature Communications, this approach enabled them to identify that purely electronic interactions likely lead to HTS.

    “Superconductivity in cuprates usually coexists with periodic arrangements of electric charge or spin and many other phenomena that can either compete with or aid superconductivity, complicating the picture,” explained first author Tonica Valla, a physicist in the Electron Spectroscopy Group of Brookhaven Lab’s Condensed Matter Physics and Materials Science Division. “But these phenomena weaken or completely vanish with overdoping, leaving nothing but superconductivity. Thus, this is the perfect region to study the origin of superconductivity. Our experiments have uncovered an interaction between electrons in BSCCO that correlates one to one with superconductivity. Superconductivity emerges exactly when this interaction first appears and becomes stronger as the interaction strengthens.”

    Only very recently has it become possible to overdope cuprate samples beyond the point where superconductivity vanishes. Previously, a bulk crystal of the material would be annealed (heated) in high-pressure oxygen gas to increase the concentration of oxygen (the dopant material). The new method—which Valla and other Brookhaven scientists first demonstrated about a year ago at OASIS, a new on-site instrument for sample preparation and characterization—uses ozone instead of oxygen to anneal cleaved samples. Cleaving refers to breaking the crystal in vacuum to create perfectly flat and clean surfaces.

    “The oxidation power of ozone, or its ability to accept electrons, is much stronger than that of molecular oxygen,” explained coauthor Ilya Drozdov, a physicist in the division’s Oxide Molecular Beam Epitaxy (OMBE) Group. “This means we can bring more oxygen into the crystal to create more holes in the copper-oxide planes, where superconductivity occurs. At OASIS, we can overdope surface layers of the material all the way to the nonsuperconducting region and study the resulting electronic excitations.”

    OASIS combines an OMBE system for growing oxide thin films with angle-resolved photoemission spectroscopy (ARPES) and spectroscopic imaging–scanning tunneling microscopy (SI-STM) instruments for studying the electronic structure of these films. Here, materials can be grown and studied using the same connected ultrahigh vacuum system to avoid oxidation and contamination by carbon dioxide, water, and other molecules in the atmosphere. Because ARPES and SI-STM are extremely surface-sensitive techniques, pristine surfaces are critical to obtaining accurate measurements.

    For this study, coauthor Genda Gu, a physicist in the division’s Neutron Scattering Group, grew bulk BSCCO crystals. Drozdov annealed the cleaved crystals in ozone in the OMBE chamber at OASIS to increase the doping until superconductivity was completely lost. The same sample was then annealed in vacuum in order to gradually reduce the doping and increase the transition temperature at which superconductivity emerges. Valla analyzed the electronic structure of BSCCO across this doping-temperature phase diagram through ARPES.

    “ARPES gives you the most direct picture of the electronic structure of any material,” said Valla. “Light excites electrons from a sample, and by measuring their energy and the angle at which they escape, you can recreate the energy and momentum of the electrons while they were still in the crystal.”

    In measuring this energy-versus-momentum relationship, Valla detected a kink (anomaly) in the electronic structure that follows the superconducting transition temperature. The kink becomes more pronounced and shifts to higher energies as this temperature increases and superconductivity gets stronger, but disappears outside of the superconducting state. On the basis of this information, he knew that the interaction creating the electron pairs required for superconductivity could not be electron-phonon coupling, as theorized for conventional superconductors. Under this theory, phonons, or vibrations of atoms in the crystal lattice, serve as an attractive force for otherwise repulsive electrons through the exchange of momentum and energy.

    “Our result allowed us to rule out electron-phonon coupling because atoms in the lattice can vibrate and electrons can interact with those vibrations, regardless of whether the material is superconducting or not,” said Valla. “If phonons were involved, we would expect to see the kink in both the superconducting and normal state, and the kink would not be changing with doping.”

    The team believes that something similar to electron-phonon coupling is going on in this case, but instead of phonons, another excitation gets exchanged between electrons. It appears that electrons are interacting through spin fluctuations, which are related to electrons themselves. Spin fluctuations are changes in electron spin, or the way that electrons point either up or down as tiny magnets.

    Moreover, the scientists found that the energy of the kink is less than that of a characteristic energy at which a sharp peak (resonance) in the spin fluctuation spectrum appears. Their finding suggests that the onset of spin fluctuations (instead of the resonance peak) is responsible for the observed kink and may be the “glue” that binds electrons into the pairs required for HTS.

    Next, the team plans to collect additional evidence showing that spin fluctuations are related to superconductivity by obtaining SI-STM measurements. They will also perform similar experiments on another well-known cuprate, lanthanum strontium copper oxide (LSCO).

    “For the first time, we are seeing something that strongly correlates with superconductivity,” said Valla. “After all these years, we now have a better grasp of what may be causing superconductivity in not only BSCCO but also other cuprates.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    BNL Campus

    Brookhaven campus

    BNL Center for Functional Nanomaterials

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL Phenix Detector

    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.

     
  • richardmitnick 9:28 am on January 4, 2020 Permalink | Reply
    Tags: "The case of the elusive Majorana: The so-called 'angel particle' still a mystery", , Condensed Matter Physics, , , ,   

    From Pennsylvania State University: “The case of the elusive Majorana: The so-called ‘angel particle’ still a mystery” 

    Penn State Bloc

    From Pennsylvania State University

    January 03, 2020
    Sam Sholtis

    1
    An exotic quantum state known as a “chiral Majorana fermion” is predicted in devices wherein a superconductor is affixed on top of a quantum anomalous Hall (QAH) insulator (left panel). Experiments performed at Penn State and the University of Würzburg in Germany show that the millimeter-size superconductor strip used in the proposed device geometry creates an electrical short, preventing the detection of chiral Majoranas (right panel). Image: Cui-Zu Chang, Penn State

    A 2017 report of the discovery of a particular kind of Majorana fermion — the chiral Majorana fermion, referred to as the “angel particle” — is likely a false alarm, according to new research. Majorana fermions are enigmatic particles that act as their own antiparticle and were first hypothesized to exist in 1937. They are of immense interest to physicists because their unique properties could allow them to be used in the construction of a topological quantum computer.

    A team of physicists at Penn State and the University of Wurzburg in Germany led by Cui-Zu Chang, an assistant professor of physics at Penn State, studied over three dozen devices similar to the one used to produce the angel particle in the 2017 report. They found that the feature that was claimed to be the manifestation of the angel particle was unlikely to be induced by the existence of the angel particle. A paper describing the research appears on Jan. 3 in the journal Science.

    “When the Italian physicist Ettore Majorana predicted the possibility of a new fundamental particle which is its own antiparticle, little could he have envisioned the long-lasting implications of his imaginative idea,” said Nitin Samarth, Downsbrough Department Head and professor of physics at Penn State. “Over 80 years after Majorana’s prediction, physicists continue to actively search for signatures of the still elusive ‘Majorana fermion’ in diverse corners of the universe.”

    In one such effort, particle physicists are using underground observatories that seek to prove whether the ghost-like particle known as the neutrino — a subatomic particle that rarely interacts with matter — might be a Majorana fermion.

    On a completely different front, condensed matter physicists are seeking to discover manifestations of Majorana physics in solid-state devices that combine exotic quantum materials with superconductors. In such devices, electrons are theorized to dress themselves as Majorana fermions by stitching together a fabric constructed from core aspects of quantum mechanics, relativistic physics, and topology. This analogous version of Majorana fermions has particularly captured the attention of condensed-matter physicists because it may provide a pathway for constructing a “topological quantum computer” whose qubits (quantum versions of binary 0s and 1s) are inherently protected from environmental decoherence — the loss of information that results when a quantum system is not perfectly isolated, and a major hurdle in the development of quantum computers.

    “An important first step toward this distant dream of creating a topological quantum computer is to demonstrate definitive experimental evidence for the existence of Majorana fermions in condensed matter,” said Chang. “Over the past seven or so years, several experiments have claimed to show such evidence, but the interpretation of these experiments is still debated.”

    The team studied devices fashioned from a quantum material known as a “quantum anomalous Hall insulator,” wherein the electrical current flows only at the edge. A recent study predicted that when the edge current is in clean contact with a superconductor, propagating chiral Majorana fermions are created and the electrical conductance of the device should be “half-quantized” — a value of e2/2h where “e” is the electron charge and “h” is Planck constant — when subject to a precise magnetic field. The Penn State-Wurzburg team studied over three dozen devices with several different materials configurations and found that devices with a clean superconducting contact always show the half-quantized value regardless of magnetic field conditions. This occurs because the superconductor acts like an electrical short and is thus not indicative of the presence of the Majorana fermion, said the researchers.

    “The fact that two laboratories — at Penn State and at Wurzburg — found completely consistent results using a wide variety of device configurations casts serious doubt on the validity of the theoretically proposed experimental geometry and questions the 2017 claim of observing the angel particle,” said Moses Chan, Evan Pugh Professor Emeritus of Physics at Penn State.

    “I remain optimistic that the combination of quantum anomalous Hall insulators and superconductivity is an attractive scheme for realizing chiral Majoranas,” said Morteza Kayyalha, a postdoctoral research associate at Penn State who carried out the device fabrication and measurements. “But our theorist colleagues need to rethink the device geometry.”

    “This is an excellent illustration of how science should work,” said Samarth. “Extraordinary claims of discovery need to be carefully examined and reproduced. All of our postdocs and students worked really hard to make sure they carried out very rigorous tests of the past claims. We are also making sure that all of our data and methods are shared transparently with the community so that our results can be critically evaluated by interested colleagues.”

    In addition to Chang, Samarth, Chan and Kayyalha, the research team includes Penn State faculty member Qi Li, and Wurzburg faculty members Laurens Molenkamp and Charles Gould. The project relied on materials synthesis carried out at Penn State’s 2D Crystal Consortium user facility for synthesis of 2D quantum materials and was funded by the U.S. National Science Foundation, the Office of Naval Research, the U.S. Department of Energy, the Army Research Office, and the European Research Council.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Penn State Campus

    About Penn State

    WHAT WE DO BEST

    We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

    Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

    We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

    Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

    The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

     
  • richardmitnick 1:27 pm on December 16, 2019 Permalink | Reply
    Tags: Condensed Matter Physics, Giulia Galli, How to harness molecular behavior to improve technology, , ,   

    From University of Chicago: Women in STEM -“Physicist taps quantum mechanics to crack molecular secrets” Giulia Galli 

    U Chicago bloc

    From University of Chicago

    Dec 16, 2019
    Louise Lerner

    1
    Prof. Giulia Galli’s work predicts how to harness molecular behavior to improve technology, such as purifying water.
    Photo by Jean Lachat

    There are few scientists who would describe condensed matter physics—a branch that studies the behavior of solid matter—as “simple.” But to Prof. Giulia Galli, it’s less complex than the problems she works on at the University of Chicago.

    “Problems like water and energy are much more complicated than what I was trained for in condensed matter physics,” she said. “All of my work is driven by problems.”

    It’s complex problems like these that the Pritzker School for Molecular Engineering—the first of its kind to focus on this emerging field—was set up to solve. And it’s the kind of innovative research that Galli, a theorist who uses computational models to figure out the behavior of molecules and materials, is helping tackle through her pioneering work.

    The focus of Galli’s studies is to understand and predict how to harness molecular behavior to improve technology, particularly in the areas of purifying water, speeding up computation and sensing with quantum technology, and perfecting renewable energy technology.

    “Essentially, we predict how atoms arrange themselves,” explained Galli, the Liew Family Professor of Molecular Engineering at UChicago. “We do this by developing theoretical algorithms and powerful codes and simulations in order to understand the quantum mechanics at play in a given material.”

    For example, her group can use theory to predict which material will make a cheaper solar cell, or suggest a new configuration for a quantum bit made from electron spins. “Energy and water are incredibly important problems—even a small improvement from your science can have a huge impact,” she said. “This is really important to me.”

    2
    One of Galli’s favorite parts of her day is working with her group, including postdoctoral researcher Elizabeth Lee (left) and graduate student Hien Vo (right). Photo by Jean Lachat

    Galli, who also heads the Midwest Integrated Center for Computational Materials, has garnered international recognition for her work in helping shape the field. She recently received the Feynman Theory Prize, an annual honor highlighting extraordinary work in harnessing quantum mechanics for the public interest. It was her fourth such major award in her field this year.

    “It is not difficult to understand why Giulia has been recognized as a scientific leader by a diverse set of scientific organizations,” said Matthew Tirrell, the founding Pritzker director and dean of the Pritzker School of Molecular Engineering. “She wields powerful and versatile computational tools that she has deployed to learn about many important scientific matters, ranging from how water behaves to materials being explored for quantum device engineering.”

    Deciphering atomic rules

    Quantum mechanics describes the rules of atomic behavior at incredibly tiny scales—a world full of the unexpected, which Galli seeks to explain using computer codes. But the challenge of modeling the interactions between hundreds of thousands of atoms in a material is a Herculean task. Often she uses the Research Computing Center at the University, but for more complex simulations, her team uses the extremely powerful supercomputers at UChicago-affiliated Argonne National Laboratory, where Galli has a joint appointment.

    The simulations may take months, depending on the problem; in fact, that Galli’s group is constantly running simulations on as many machines as they can get ahold of: “We’re running simulations every day, many at the same time. We probably have 15 projects running right now,” she said.

    _______________________________________
    “The job of a good scientist is to constantly doubt your answers.”
    —Prof. Giulia Galli
    _______________________________________

    At the same time, she’s usually writing four or five papers at any given time; in between, she’s traveling to conferences, teaching, or working with students and postdoctoral researchers in her group.

    Her field has changed a great deal over the years, as computers and data capacity have improved, but to Galli, it keeps her energized. “The problems are always changing. Nothing is ever boring.”

    Since she moved to the PME from the University of California-Davis, she’s been able to work much more closely with scientists on the experimental side, creating a loop where their experiments validate and explore her theoretical predictions, and her insights suggest new avenues for experiments.

    One such collaborator is David Awschalom, the Liew Family professor in molecular engineering and director of the Chicago Quantum Exchange, who has worked with Galli for years at PME.

    “Giulia’s innovative work on exploring materials for quantum information science and technology is guiding research programs at the University of Chicago and around the world,” said Awschalom. “Her innovative research is based on identifying important problems in materials science, developing a unique theoretical approach that is informed by experimental measurement, and ultimately resolving outstanding questions about the dynamics of complex systems with predictive models.”

    Addressing a ‘data crisis’

    More recently, she’s become interested in addressing a problem in the field of science known as the data reproducibility crisis. All good experiments and calculations have to be able to produce the same results, no matter who’s doing the experiment or carrying out the simulations; but as simulations grow more complex and the amount of data skyrockets, it becomes harder for other scientists to be able to check someone’s work.

    3
    A recent Galli study examined inorganic links between nanoparticles for applications in solar panels and optical devices.
    Illustration by Peter Allen.

    Galli began providing links for interested parties to download the data (and codes) from her work, but that was only a local solution. To address the problem on a larger scale, Galli created a publicly available tool called Qresp that provides a framework for researchers to share their data and workflows, so that others can see how the results were reached—and try to poke holes in it.

    She sees this as essential for science—and for scientists.

    “The job of a good scientist is to constantly doubt your answers,” Galli said. “The minute you get results, you have to think about how to validate them. How to find a different way to evaluate them. To push and challenge yourself. To do what you don’t yet know how to do. That’s what I tell my graduate students.

    “The real job of a scientist is to come up with a way to solve a problem that nobody else knows how to solve. And then to challenge yourself, over and over again, to make sure your solution is correct and robust.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Chicago Campus

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

     
  • richardmitnick 1:10 pm on December 6, 2019 Permalink | Reply
    Tags: "A platform for stable quantum computing, a playground for exotic physics", , Condensed Matter Physics, , , , Topological insulators are materials that can conduct electricity on their surface or edge but not in the middle.   

    From Harvard Gazette: “A platform for stable quantum computing, a playground for exotic physics” 

    Harvard University


    From Harvard Gazette

    December 5, 2019
    Leah Burrows

    1
    A close-up view of a quantum computer. Courtesy of Harvard SEAS

    Recent research settles a long-standing debate.

    Move over Godzilla vs. King Kong. This is the crossover event you’ve been waiting for — at least if you’re a condensed-matter physicist. Harvard University researchers have demonstrated the first material that can have both strongly correlated electron interactions and topological properties.

    Not sure what that means? Don’t worry, we’ll walk you through it. But the important thing to know is that this discovery not only paves the way for more stable quantum computing, but also creates an entirely new platform to explore the wild world of exotic physics.

    The research was published in Nature Physics.

    Let’s start with the basics. Topological insulators are materials that can conduct electricity on their surface or edge, but not in the middle. The strange thing about these materials is that no matter how you cut them, the surface will always be conducting and the middle always insulating. These materials offer a playground for fundamental physics, and are also promising for a number of applications in special types of electronics and quantum computing.

    Since the discovery of topological insulators, researchers around the world have been working to identify materials with these powerful properties.

    “A recent boom in condensed-matter physics has come from discovering materials with topologically protected properties,” said Harris Pirie, a graduate student in the Department of Physics and first author of the paper.

    One potential material, samarium hexaboride, has been at the center of a fierce debate among condensed-matter physicists for more than a decade. At issue: Is it or isn’t it a topological insulator?

    “Over the last 10 years, a bunch of papers have come out saying yes and a bunch of papers have come out saying no,” said Pirie. “The crux of the issue is that most topological materials don’t have strongly interacting electrons, meaning the electrons move too quickly to feel each other. But samarium hexaboride does, meaning that electrons inside this material slow down enough to interact strongly. In this realm, the theory gets fairly speculative and it’s been unclear whether or not it’s possible for materials with strongly interacting properties to also be topological. As experimentalists, we’ve been largely operating blind with materials like this.”

    In order to settle the debate and figure out, once and for all, whether it’s possible to have both strongly interacting and topological properties, the researchers first needed to find a well-ordered patch of samarium hexaboride surface on which to perform the experiment.

    2
    A simulation of electrons scattering off atomic defects in samarium hexaboride. By observing the waves, the researchers could figure out the momentum of the electrons in relation to their energy. Video courtesy of Harris Pirie/Harvard University

    It was no easy task, considering the majority of the material surface is a craggy, disordered mess. The researchers used ultrahigh precision measurement tools developed in the lab of Jenny Hoffman, the Clowes Professor of Science and senior author of the paper, to find a suitable, atomic-scale patch of samarium hexaboride.

    Next, the team set out to determine if the material was topologically insulating by sending waves of electrons through the material and scattering them off of atomic defects — like dropping a pebble into a pond. By observing the waves, the researchers could figure out the momentum of the electrons in relation to their energy.

    “We found that the momentum of the electrons is directly proportional to their energy, which is the smoking gun of a topological insulator,” said Pirie. “It’s really exciting to be finally moving into this intersection of interacting physics and topological physics. We don’t know what we’ll find here.”

    As it relates to quantum computing, strongly interacting topological materials may be able to protect qubits from forgetting their quantum state, a process called decoherence.

    “If we could encode the quantum information in a topologically protected state, it is less susceptible to external noise that can accidentally switch the qubit,” said Hoffman. “Microsoft already has a large team pursuing topological quantum computation in composite materials and nanostructures. Our work demonstrates a first in a single topological material that harnesses strong electron interactions that might eventually be used for topological quantum computing.”

    “The next step will be to use the combination of topologically protected quantum states and strong interactions to engineer novel quantum states of matter, such as topological superconductors,” said Dirk Morr, professor of physics at the University of Illinois, Chicago, and the senior theorist on the paper. “Their extraordinary properties could open unprecedented possibilities for the implementation of topological quantum bits.”

    This research was co-authored by Yu Liu, Anjan Soumyanarayanan, Pengcheng Chen, Yang He, M.M. Yee, P.F.S. Rosa, J.D. Thompson, Dae-Jeong Kim, Z. Fisk, Xiangfeng Wang, Johnpierre Paglione, and M.H. Hamidian.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Harvard University campus
    Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

     
  • richardmitnick 9:15 pm on September 16, 2019 Permalink | Reply
    Tags: 21st century alchemy, , Condensed Matter Physics, , , Plasmons   

    From Niels Bohr Institute: “Quantum Alchemy: Researchers use laser light to transform metal into magnet” 

    University of Copenhagen

    Niels Bohr Institute bloc

    From Niels Bohr Institute

    16 September 2019

    Mark Spencer Rudner
    Associate Professor
    Condensed Matter Physics
    Niels Bohr Institutet
    rudner@nbi.ku.dk

    Maria Hornbek
    Journalist
    The Faculty of Science
    maho@science.ku.dk
    +45 22 95 42 83

    CONDENSED MATTER PHYSICS: Pioneering physicists from the University of Copenhagen and Nanyang Technological University in Singapore have discovered a way to get non-magnetic materials to make themselves magnetic by way of laser light. The phenomenon may also be used to endow many other materials with new properties.

    1
    Mark Rudner, Niels Bohr Institute, University of Copenhagen

    2
    Asst Prof Justin Song Chien Wen

    The intrinsic properties of materials arise from their chemistry — from the types of atoms that are present and the way that they are arranged. These factors determine, for example, how well a material may conduct electricity or whether or not it is magnetic. Therefore, the traditional route for changing or achieving new material properties has been through chemistry.

    Now, a pair of researchers from the University of Copenhagen and Nanyang Technological University in Singapore have discovered a new physical route to the transformation of material properties: when stimulated by laser light, a metal can transform itself from within and suddenly acquire new properties.

    1

    “For several years, we have been looking into how to transform the properties of a matter by irradiating it with certain types of light. What’s new is that not only can we change the properties using light, we can trigger the material to change itself, from the inside out, and emerge into a new phase with completely new properties. For instance, a non-magnetic metal can suddenly transform into a magnet,” explains Associate Professor Mark Rudner, a researcher at the University of Copenhagen’s Niels Bohr Institute.

    He and colleague Justin Song of Nanyang Technological University in Singapore made the discovery that is now published in Nature Physics. The idea of using light to transform the properties of a material is not novel in itself. But up to now, researchers have only been capable of manipulating the properties already found in a material. Giving a metal its own ‘separate life’, allowing it to generate its own new properties, has never been seen before.

    By way of theoretical analysis, the researchers have succeeded in proving that when a non-magnetic metallic disk is irradiated with linearly polarized light, circulating electric currents and hence magnetism can spontaneously emerge in the disk.

    Researchers use so-called plasmons (a type of electron wave) found in the material to change its intrinsic properties. When the material is irradiated with laser light, plasmons in the metal disk begin to rotate in either a clockwise or counterclockwise direction. However, these plasmons change the quantum electronic structure of a material, which simultaneously alters their own behavior, catalyzing a feedback loop. Feedback from the plasmons’ internal electric fields eventually causes the plasmons to break the intrinsic symmetry of the material and trigger an instability toward self-rotation that causes the metal to become magnetic.

    Technique can produce properties ‘on demand’

    According to Mark Rudner, the new theory pries open an entire new mindset and most likely, a wide range of applications:

    “It is an example of how the interaction between light and material can be used to produce certain properties in a material ‘on demand’. It also paves the way for a multitude of uses, because the principle is quite general and can work on many types of materials. We have demonstrated that we can transform a material into a magnet. We might also be able to change it into a superconductor or something entirely different,” says Rudner. He adds:

    “You could call it 21st century alchemy. In the Middle Ages, people were fascinated by the prospect of transforming lead into gold. Today, we aim to get one material to behave like another by stimulating it with a laser.”

    Among the possibilities, Rudner suggests that the principle could be useful in situations where one needs a material to alternate between behaving magnetically and not. It could also prove useful in opto-electronics – where, for example, light and electronics are combined for fiber-internet and sensor development.

    The researchers’ next steps are to expand the catalog of properties that can be altered in analogous ways, and to help stimulate their experimental investigation and utilization.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings


    Stem Education Coalition

    Niels Bohr Institute Campus

    Niels Bohr Institute (Danish: Niels Bohr Institutet) is a research institute of the University of Copenhagen. The research of the institute spans astronomy, geophysics, nanotechnology, particle physics, quantum mechanics and biophysics.

    The Institute was founded in 1921, as the Institute for Theoretical Physics of the University of Copenhagen, by the Danish theoretical physicist Niels Bohr, who had been on the staff of the University of Copenhagen since 1914, and who had been lobbying for its creation since his appointment as professor in 1916. On the 80th anniversary of Niels Bohr’s birth – October 7, 1965 – the Institute officially became The Niels Bohr Institute.[1] Much of its original funding came from the charitable foundation of the Carlsberg brewery, and later from the Rockefeller Foundation.[2]

    During the 1920s, and 1930s, the Institute was the center of the developing disciplines of atomic physics and quantum physics. Physicists from across Europe (and sometimes further abroad) often visited the Institute to confer with Bohr on new theories and discoveries. The Copenhagen interpretation of quantum mechanics is named after work done at the Institute during this time.

    On January 1, 1993 the institute was fused with the Astronomic Observatory, the Ørsted Laboratory and the Geophysical Institute. The new resulting institute retained the name Niels Bohr Institute.

    The University of Copenhagen (UCPH) (Danish: Københavns Universitet) is the oldest university and research institution in Denmark. Founded in 1479 as a studium generale, it is the second oldest institution for higher education in Scandinavia after Uppsala University (1477). The university has 23,473 undergraduate students, 17,398 postgraduate students, 2,968 doctoral students and over 9,000 employees. The university has four campuses located in and around Copenhagen, with the headquarters located in central Copenhagen. Most courses are taught in Danish; however, many courses are also offered in English and a few in German. The university has several thousands of foreign students, about half of whom come from Nordic countries.

    The university is a member of the International Alliance of Research Universities (IARU), along with University of Cambridge, Yale University, The Australian National University, and UC Berkeley, amongst others. The 2016 Academic Ranking of World Universities ranks the University of Copenhagen as the best university in Scandinavia and 30th in the world, the 2016-2017 Times Higher Education World University Rankings as 120th in the world, and the 2016-2017 QS World University Rankings as 68th in the world. The university has had 9 alumni become Nobel laureates and has produced one Turing Award recipient

     
  • richardmitnick 7:16 pm on May 22, 2019 Permalink | Reply
    Tags: , , carbon and ice, , Condensed Matter Physics, , Most people behave differently when under extreme pressure. Carbon and ice are no different., ,   

    From UCLA Newsroom: “New insights about carbon and ice could clarify inner workings of Earth, other planets” 


    From UCLA Newsroom

    Media Contact

    Stuart Wolpert
    UCLA
    310-206-0511
    swolpert@stratcomm.ucla.edu

    May 22, 2019
    Christopher Crockett

    1
    New simulations suggest that carbon (C) routinely bonded with iron (Fe), silicon (Si) and oxygen (O) deep within the magma ocean that covered Earth when it was young. Natalia Solomatova/École Normale Supérieure de Lyon.

    2
    ORNL super-cold states of water. phys.org

    Most people behave differently when under extreme pressure. Carbon and ice are no different.

    Two new studies show how these key planetary ingredients take on exotic forms that could help researchers better understand the composition of Earth’s core as well as the cores of planets across the galaxy. Craig Manning, a UCLA professor of geology and geochemistry, is a co-senior author of one of the papers, which was published today in the journal Nature, and senior author of the other, which was published in Nature Communications in February.

    The Nature Communications paper revealed that high pressure deep inside the young Earth may have driven vast stores of carbon into the planet’s core while also setting the stage for diamonds to form. In the Nature report, researchers found that water ice undergoes a complex crystalline metamorphosis as the pressure slowly ratchets up.

    Scientists have long understood that the amount of carbon sequestered in present-day Earth’s rocks, oceans and atmosphere is always in flux because the planet shuffles the element around in a vast cycle that helps regulate climate. But researchers don’t know whether the Earth locked away even more carbon deep in its interior during its formative years — information that could reveal a little more about how our planet and others like it are built.

    To pursue an answer to that question, Manning and colleagues calculated how carbon might have interacted with other atoms under conditions similar to those that prevailed roughly 4.5 billion years ago, when much of Earth was still molten. Using supercomputers, the team created simulations to explore what would happen to carbon at temperatures above 3,000 degrees Celsius (more than 5,400 degrees Fahrenheit) and at pressures more than 100,000 times of those on Earth’s surface today.

    The experiment revealed that under those conditions, carbon tends to link up with iron, which implies that there might be considerable quantities of carbon sealed in Earth’s iron core today. Researchers had already suspected that in the young planet’s magma ocean, iron atoms hooked up with one another and then dropped to the planet’s center. But the new research suggests that this molten iron rain may have also dragged carbon down with it. Until now, researchers weren’t even sure whether carbon exists down there.

    The team also found that as the pressure ramps up, carbon increasingly bonds with itself, forming long chains of carbon atoms with oxygen atoms sticking out.

    “These complex chains are a form of carbon bonding that we really hadn’t anticipated at these conditions,” Manning said.

    Such molecules could be a precursor to diamonds, which consist of many carbon atoms linked together.

    Solving an icy enigma

    The machinations of carbon under pressure provide clues as to how Earth-like planets are built. Frozen planets and moons in other solar systems, however, may also have to contend with water ice. In a separate paper, Manning and another team of scientists looked at how the molecular structure of extremely cold ice changes when put under intense pressure.

    Under everyday conditions, water ice is made up of molecules laid out in honeycomb-like mosaics of hexagons. But when ice is exposed to crushing pressure or very low temperature — in labs or possibly deep inside remote worlds — the molecules can assume a bewildering variety of patterns.

    One of those patterns, known as amorphous ice, is an enigma. In amorphous ice, the water molecules eschew rigid crystalline order and take on a free-form arrangement. Manning and colleagues set out to try and understand how amorphous ice forms.

    First, they chilled normal ice to about 170 degrees below zero Celsius (about 274 degrees below zero Fahrenheit). Then, they locked the ice in the jaws of a high-tech vice grip inside a cryogenic vacuum chamber. Finally, over the span of several hours, they slowly stepped up the pressure in the chamber to about 15,000 times atmospheric pressure. They stopped raising the pressure periodically to fire neutrons through the ice so that they could see the arrangement of the water molecules.

    Surprisingly to the researchers, the amorphous ice never formed. Instead, the molecules went through a series of previously known crystalline arrangements.

    However, when the researchers conducted the same experiment but raised the pressure much more rapidly — this time in just 30 minutes — amorphous ice formed as expected. The results suggest that time is the secret ingredient: When pressure increases slowly, tiny seeds of crystalline ice have time to form and take over the sample. Otherwise, those seeds never get a chance to grow.

    The findings, published May 23 in the journal Nature [above], could be useful to researchers who study worlds orbiting other suns and are curious about what conditions might be like deep inside frozen planets.

    “It’s entirely likely that there are planets dominated by ice in other solar systems that could obtain these pressures and temperatures with ease,” Manning said. “We have to have this right if we’re going to have a baseline for understanding the interiors of cold worlds that may not be like Earth.”

    Both papers were funded in part by the Deep Carbon Observatory, a 10-year program started in 2009 to investigate the quantities, movements, forms and origins of deep carbon inside Earth. The Nature Communications paper was also funded by the European Research Council and was co-authored by researchers at the Ecole Normale Supérieure de Lyon in France, one of whom — Natalia Solomatova — completed her undergraduate studies at UCLA. The Nature paper was co-authored by UCLA geologist Adam Makhluf and researchers from Oak Ridge National Laboratory and the National Research Council of Canada.

    See the full article here .
    See also in phys.org here.


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    UC LA Campus

    For nearly 100 years, UCLA has been a pioneer, persevering through impossibility, turning the futile into the attainable.

    We doubt the critics, reject the status quo and see opportunity in dissatisfaction. Our campus, faculty and students are driven by optimism. It is not naïve; it is essential. And it has fueled every accomplishment, allowing us to redefine what’s possible, time after time.

    This can-do perspective has brought us 12 Nobel Prizes, 12 Rhodes Scholarships, more NCAA titles than any university and more Olympic medals than most nations. Our faculty and alumni helped create the Internet and pioneered reverse osmosis. And more than 100 companies have been created based on technology developed at UCLA.

     
  • richardmitnick 12:50 pm on April 5, 2019 Permalink | Reply
    Tags: "Putting a New Spin on Majorana Fermions", , , Condensed Matter Physics, Majorana fermions are particle-like excitations called quasiparticles that emerge as a result of the fractionalization (splitting) of individual electrons into two halves., , , , , Spin ladders- crystals formed of atoms with a three-dimensional (3-D) structure subdivided into pairs of chains that look like ladders.   

    From Brookhaven National Lab: “Putting a New Spin on Majorana Fermions” 

    From Brookhaven National Lab

    April 1, 2019
    Ariana Tantillo
    atantillo@bnl.gov
    (631) 344-2347

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

    Split electrons that emerge at the boundaries between different magnetic states in materials known as spin ladders could act as stable bits of information in next-generation quantum computers.

    2
    Theoretical calculations performed by (left to right) Neil Robinson, Robert Konik, Alexei Tsvelik, and Andreas Weichselbaum of Brookhaven Lab’s Condensed Matter Physics and Materials Science Department suggest that Majorana fermions exist in the boundaries of magnetic materials with different magnetic phases. Majorana fermions are particle-like excitations that emerge when single electrons fractionalize into two halves, and their unique properties are of interest for quantum applications.

    The combination of different phases of water—solid ice, liquid water, and water vapor—would require some effort to achieve experimentally. For instance, if you wanted to place ice next to vapor, you would have to continuously chill the water to maintain the solid phase while heating it to maintain the gas phase.

    For condensed matter physicists, this ability to create different conditions in the same system is desirable because interesting phenomena and properties often emerge at the interfaces between two phases. Of current interest is the conditions under which Majorana fermions might appear near these boundaries.

    Majorana fermions are particle-like excitations called quasiparticles that emerge as a result of the fractionalization (splitting) of individual electrons into two halves. In other words, an electron becomes an entangled (linked) pair of two Majorana quasiparticles, with the link persisting regardless of the distance between them. Scientists hope to use Majorana fermions that are physically separated in a material to reliably store information in the form of qubits, the building blocks of quantum computers. The exotic properties of Majoranas—including their high insensitivity to electromagnetic fields and other environmental “noise”—make them ideal candidates for carrying information over long distances without loss.

    However, to date, Majorana fermions have only been realized in materials at extreme conditions, including at frigid temperatures close to absolute zero (−459 degrees Fahrenheit) and under high magnetic fields. And though they are “topologically” protected from local atomic impurities, disorder, and defects that are present in all materials (i.e., their spatial properties remain the same even if the material is bent, twisted, stretched, or otherwise distorted), they do not survive under strong perturbations. In addition, the range of temperatures over which they can operate is very narrow. For these reasons, Majorana fermions are not yet ready for practical technological application.

    Now, a team of physicists led by the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and including collaborators from China, Germany, and the Netherlands has proposed a novel theoretical method for producing more robust Majorana fermions. According to their calculations, as described in a paper published on Jan. 15 in Physical Review Letters, these Majoranas emerge at higher temperatures (by many orders of magnitude) and are largely unaffected by disorder and noise. Even though they are not topologically protected, they can persist if the perturbations change slowly from one point to another in space.

    “Our numerical and analytical calculations provide evidence that Majorana fermions exist in the boundaries of magnetic materials with different magnetic phases, or directions of electron spins, positioned next to one other,” said co-author Alexei Tsvelik, senior scientist and leader of the Condensed Matter Theory Group in Brookhaven Lab’s Condensed Matter Physics and Materials Science (CMPMS) Department. “We also determined the number of Majorana fermions you should expect to get if you combine certain magnetic phases.”

    For their theoretical study, the scientists focused on magnetic materials called spin ladders, which are crystals formed of atoms with a three-dimensional (3-D) structure subdivided into pairs of chains that look like ladders. Though the scientists have been studying the properties of spin ladder systems for many years and expected that they would produce Majorana fermions, they did not know how many. To perform their calculations, they applied the mathematical framework of quantum field theory for describing the fundamental physics of elementary particles, and a numerical method (density-matrix renormalization group) for simulating quantum systems whose electrons behave in a strongly correlated way.

    “We were surprised to learn that for certain configurations of magnetic phases we can generate more than one Majorana fermion at each boundary,” said co-author and CMPMS Department Chair Robert Konik.

    For Majorana fermions to be practically useful in quantum computing, they need to be generated in large numbers. Computing experts believe that the minimum threshold at which quantum computers will be able to solve problems that classical computers cannot is 100 qubits. The Majorana fermions also have to be moveable in such a way that they can become entangled.

    The team plans to follow up their theoretical study with experiments using engineered systems such as quantum dots (nanosized semiconducting particles) or trapped (confined) ions. Compared to the properties of real materials, those of engineered ones can be more easily tuned and manipulated to introduce the different phase boundaries where Majorana fermions may emerge.

    “What the next generation of quantum computers will be made of is unclear right now,” said Konik. “We’re trying to find better alternatives to the low-temperature superconductors of the current generation, similar to how silicon replaced germanium in transistors. We’re in such early stages that we need to explore every possibility available.”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    BNL Campus

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    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.
    i1

     
  • richardmitnick 3:38 pm on January 3, 2019 Permalink | Reply
    Tags: , Condensed Matter Physics, , Electron spin, , SARPES detector, ,   

    From Lawrence Berkeley National Lab: “Revealing Hidden Spin: Unlocking New Paths Toward High-Temperature Superconductors” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    January 3, 2019

    Theresa Duque
    tnduque@lbl.gov
    (510) 495-2418

    Berkeley Lab researchers uncover insights into superconductivity, leading potentially to more efficient power transmission.

    1
    A research team led by Berkeley Lab’s Alessandra Lanzara (second from left) used a SARPES (spin- and angle-resolved photoemission spectroscopy) detector to uncover a distinct pattern of electron spins within the material. Co-lead authors are Kenneth Gotlieb (second from right) and Chiu-Yun Lin (right). The study’s co-authors include Chris Jozwiak of Berkeley Lab’s Advanced Light Source (left). (Credit: Peter DaSilva/Berkeley Lab)

    In the 1980s, the discovery of high-temperature superconductors known as cuprates upended a widely held theory that superconductor materials carry electrical current without resistance only at very low temperatures of around 30 Kelvin (or minus 406 degrees Fahrenheit). For decades since, researchers have been mystified by the ability of some cuprates to superconduct at temperatures of more than 100 Kelvin (minus 280 degrees Fahrenheit).

    Now, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have unveiled a clue into the cuprates’ unusual properties – and the answer lies within an unexpected source: the electron spin. Their paper describing the research behind this discovery was published on Dec. 13 in the journal Science.

    Adding electron spin to the equation

    Every electron is like a tiny magnet that points in a certain direction. And electrons within most superconductor materials seem to follow their own inner compass. Rather than pointing in the same direction, their electron spins haphazardly point every which way – some up, some down, others left or right.

    2
    With the spin resolution enabled by SARPES, Berkeley Lab researchers revealed magnetic properties of Bi-2212 that have gone unnoticed in previous studies. (Credit: Kenneth Gotlieb, Chiu-Yun Lin, et al./Berkeley Lab)

    When scientists are developing new kinds of materials, they usually look at the materials’ electron spin, or the direction in which the electrons are pointing. But when it comes to making superconductors, condensed matter physicists haven’t traditionally focused on spin, because the conventionally held view was that all of the properties that make these materials unique were shaped only by the way in which two electrons interact with each other through what’s known as “electron correlation.”

    But when a research team led by Alessandra Lanzara, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a Charles Kittel Professor of Physics at UC Berkeley, used a unique detector to measure samples of an exotic cuprate superconductor, Bi-2212 (bismuth strontium calcium copper oxide), with a powerful technique called SARPES (spin- and angle-resolved photoemission spectroscopy), they uncovered something that defied everything they had ever known about superconductors: a distinct pattern of electron spins within the material.

    “In other words, we discovered that there was a well-defined direction in which each electron was pointing given its momentum, a property also known as spin-momentum locking,” said Lanzara. “Finding it in high-temperature superconductors was a big surprise.”

    A new map for high-temperature superconductors

    In the world of superconductors, “high temperature” means that the material can conduct electricity without resistance at temperatures higher than expected but still in extremely cold temperatures far below zero degrees Fahrenheit. That’s because superconductors need to be extraordinarily cold to carry electricity without any resistance. At those low temperatures, electrons are able to move in sync with each other and not get knocked by jiggling atoms, causing electrical resistance.

    And within this special class of high-temperature superconductor materials, cuprates are some of the best performers, leading some researchers to believe that they have potential use as a new material for building super-efficient electrical wires that can carry power without any loss of electron momentum, said co-lead author Kenneth Gotlieb, who was a Ph.D. student in Lanzara’s lab at the time of the discovery. Understanding what makes some exotic cuprate superconductors such as Bi-2212 work at temperatures as high as 133 Kelvin (about -220 degrees Fahrenheit) could make it easier to realize a practical device.

    Among the very exotic materials that condensed matter physicists study, there are two kinds of electron interactions that give rise to novel properties for new materials, including superconductors, said Gotlieb. Scientists who have been studying cuprate superconductors have focused on just one of those interactions: electron correlation.

    The other kind of electron interaction found in exotic materials is “spin-orbit coupling” – the way in which the electron’s magnetic moment interacts with atoms in the material.

    Spin-orbit coupling was often neglected in the studies of cuprate superconductors, because many assumed that this kind of electron interaction would be weak when compared to electron correlation, said co-lead author Chiu-Yun Lin, a researcher in the Lab’s Materials Sciences Division and a Ph.D. student in the Department of Physics at UC Berkeley. So when they found the unusual spin pattern, Lin said that although they were pleasantly surprised by this initial finding, they still weren’t sure whether it was a “true” intrinsic property of the Bi-2212 material, or an external effect caused by the way the laser light interacted with the material in the experiment.

    Shining a light on electron spin with SARPES

    Over the course of nearly three years, Gotlieb and Lin used the SARPES detector to thoroughly map out the spin pattern at Lanzara’s lab. When they needed higher photon energies to excite a wider range of electrons within a sample, the researchers moved the detector next door to Berkeley Lab’s synchrotron, the Advanced Light Source (ALS), a U.S. DOE Office of Science User Facility that specializes in lower energy, “soft” X-ray light for studying the properties of materials.

    LBNL/ALS

    The SARPES detector was developed by Lanzara, along with co-authors Zahid Hussain, the former ALS Division Deputy, and Chris Jozwiak, an ALS staff scientist. The detector allowed the scientists to probe key electronic properties of the electrons such as valence band structure.

    After tens of experiments at the ALS, where the team of researchers connected the SARPES detector to Beamline 10.0.1 so they could access this powerful light to explore the spin of the electrons moving with much higher momentum through the superconductor than those they could access in the lab, they found that Bi-2212’s distinct spin pattern – called “nonzero spin – was a true result, inspiring them to ask even more questions. “There remains many unsolved questions in the field of high-temperature superconductivity,” said Lin. “Our work provides new knowledge to better understand the cuprate superconductors, which can be a building block to resolve these questions.”

    Lanzara added that their discovery couldn’t have happened without the collaborative “team science” of Berkeley Lab, a DOE national lab with historic ties to nearby UC Berkeley. “This work is a typical example of where science can go when people with expertise across the scientific disciplines come together, and how new instrumentation can push the boundaries of science,” she said.

    Co-authors with Gotlieb, Lin, and Lanzara are Maksym Serbyn of the Institute of Science and Technology Austria, Wentao Zhang of Shanghai Jiao Tong University, Christopher L. Smallwood of San Jose State University, Christopher Jozwiak of Berkeley Lab, Hiroshi Eisaki of the National Institute of Advanced Industrial Science and Technology of Japan, Zahid Hussain of Berkeley Lab, and Ashvin Vishwanath, formerly of UC Berkeley and now with Harvard University and a Faculty Scientist in Berkeley Lab’s Materials Sciences Division.

    The work was supported by the DOE Office of Science.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Bringing Science Solutions to the World

    In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

    Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

    Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

    A U.S. Department of Energy National Laboratory Operated by the University of California.

    University of California Seal

    DOE Seal

     
  • richardmitnick 10:11 am on November 2, 2018 Permalink | Reply
    Tags: "In materials hit with light", , Condensed Matter Physics, individual atoms and vibrations take disorderly paths", , , , ,   

    From SLAC Lab: “In materials hit with light, individual atoms and vibrations take disorderly paths” 


    From SLAC Lab

    November 1, 2018
    Glennda Chui

    1
    Two studies with a new X-ray laser technique reveal for the first time how individual atoms and vibrations respond when a material is hit with light. Their surprisingly unpredictable behavior has profound implications for designing and controlling materials. (Greg Stewart/SLAC National Accelerator Laboratory)

    Revealed for the first time by a new X-ray laser technique, their surprisingly unruly response has profound implications for designing and controlling materials.

    Hitting a material with laser light sends vibrations rippling through its latticework of atoms, and at the same time can nudge the lattice into a new configuration with potentially useful properties – turning an insulator into a metal, for instance.

    Until now, scientists assumed this all happened in a smooth, coordinated way. But two new studies show it doesn’t: When you look beyond the average response of atoms and vibrations to see what they do individually, the response, they found, is disorderly.

    Atoms don’t move smoothly into their new positions, like band members marching down a field; they stagger around like partiers leaving a bar at closing time.

    And laser-triggered vibrations don’t simply die out; they trigger smaller vibrations that trigger even smaller ones, spreading out their energy in the form of heat, like a river branching into a complex network of streams and rivulets.

    This unpredictable behavior at a tiny scale, measured for the first time with a new X-ray laser technique at the Department of Energy’s SLAC National Accelerator Laboratory, will have to be taken into account from now on when studying and designing new materials, the researchers said – especially quantum materials with potential applications in sensors, smart windows, energy storage and conversion and super-efficient electrical conductors.

    Two separate international teams, including researchers at SLAC and Stanford University who developed the technique, reported the results of their experiments Sept. 20 in Physical Review Letters and today in Science.

    “The disorder we found is very strong, which means we have to rethink how we study all of these materials that we thought were behaving in a uniform way,” said Simon Wall, an associate professor at the Institute of Photonic Sciences in Barcelona and one of three leaders of the study reported in Science. “If our ultimate goal is to control the behavior of these materials so we can switch them back and forth from one phase to another, it’s much harder to control the drunken choir than the marching band.”

    Lifting the haze

    The classic way to determine the atomic structure of a molecule, whether from a manmade material or a human cell, is to hit it with X-rays, which bounce off and scatter into a detector. This creates a pattern of bright dots, called Bragg peaks, that can be used to reconstruct how its atoms are arranged.

    SLAC’s Linac Coherent Light Source (LCLS), with its super-bright and ultrafast X-ray laser pulses, has allowed scientists to determine atomic structures in ever more detail.

    SLAC/LCLS

    They can even take rapid-fire snapshots of chemical bonds breaking, for instance, and string them together to make “molecular movies.”

    About a dozen years ago, David Reis, a professor at SLAC and Stanford and investigator at the Stanford Institute for Materials and Energy Sciences (SIMES), wondered if a faint haze between the bright spots in the detector – 10,000 times weaker than those bright spots, and considered just background noise – could also contain important information about rapid changes in materials induced by laser pulses.

    He and SIMES scientist Mariano Trigo went on to develop a technique called “ultrafast diffuse scattering” that extracts information from the haze to get a more complete picture of what’s going on and when.

    The two new studies represent the first time the technique has been used to observe details of how energy dissipates in materials and how light triggers a transition from one phase, or state, of a material to another, said Reis, who along with Trigo is a co-author of both papers. These responses are interesting both for understanding the basic physics of materials and for developing applications that use light to switch the properties of materials on and off or convert heat to electricity, for instance.

    “It’s sort of like astronomers studying the night sky,” said Olivier Delaire, an associate professor at Duke University who helped lead one of the studies. “Previous studies could only see the brightest stars visible to the naked eye. But with the ultrabright and ultrafast X-ray pulses, we were able to see the faint and diffuse signals of the Milky Way galaxy between them.”

    Tiny bells and piano strings

    In the study published in Physical Review Letters, Reis and Trigo led a team that investigated vibrations called phonons that rattle the atomic lattice and spread heat through a material.

    The researchers knew going in that phonons triggered by laser pulses decay, releasing their energy throughout the atomic lattice. But where does all that energy go? Theorists proposed that each phonon must trigger other, smaller phonons, which vibrate at higher frequencies and are harder to detect and measure, but these had never been seen in an experiment.

    To study this process at LCLS, the team hit a thin film of bismuth with a pulse of optical laser light to set off phonons, followed by an X-ray laser pulse about 50 quadrillionths of a second later to record how the phonons evolved. The experiments were led by graduate student Tom Henighan and postdoctoral researcher Samuel Teitelbaum of the Stanford PULSE Institute.

    For the first time, Trigo said, they were able to observe and measure how the initial phonons distributed their energy over a wider area by triggering smaller vibrations. Each of those small vibrations emanated from a distinct patch of atoms, and the size of the patch – whether it contained 7 atoms, or 9, or 20 – determined the frequency of the vibration. It was much like how ringing a big bell sets smaller bells tinkling nearby, or how plucking a piano string sets other strings humming.

    “This is something we’ve been waiting years to be able to do, so we were excited,” Reis said. “It’s a measurement of something absolutely fundamental to modern solid-state physics, for everything from how heat flows in materials to even, in principle, how light-induced superconductivity emerges, and it could not have been done without an X-ray free-electron laser like LCLS.”

    A disorderly march

    The paper in Science describes LCLS experiments with vanadium dioxide, a well-studied material that can flip from being an insulator to an electrical conductor in just 100 quadrillionths of a second.

    Researchers already knew how to trigger this switch with very short, ultrafast pulses of laser light. But until now they could only observe the average response of the atoms, which seemed to shuffle into their new positions in an orderly way, said Delaire, who led the study with Wall and Trigo.

    The new round of diffuse scattering experiments at LCLS showed otherwise. By hitting the vanadium dioxide with an optical laser of just the right energy, the researchers were able to trigger a substantial rearrangement of the vanadium atoms. They did this more than 100 times per second while recording the movements of individual atoms with the LCLS X-ray laser. They discovered that each atom followed an independent, seemingly random path to its new lattice position. Computer simulations by Duke graduate student Shan Yang backed up that conclusion.

    “Our findings suggest that disorder may play an important role in some materials,” the team wrote in the Science paper. While this may complicate efforts to control the way materials shift from one phase to another, they added, “it could ultimately provide a new perspective on how to control matter,” and even suggest a new way to induce superconductivity with light.

    In a commentary accompanying the report in Science, Andrea Cavalleri of Oxford University and the Max Planck Institute for the Structure and Dynamics of Matter said the results imply that molecular movies of atoms changing position over time don’t paint a complete picture of the microscopic physics involved.

    He added, “More generally, it is clear from this work that x-ray free electron lasers are opening up far more than what was envisaged when these machines were being planned, forcing us to reevaluate many old notions taken for granted up to now.”

    The study published in PRL also involved researchers from Imperial College London; Tyndall National Institute in Ireland; and the University of Michigan, Ann Arbor. Preliminary measurements were performed at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL). Major funding came from the DOE Office of Science.

    SLAC/SSRL

    The study published in Science also involved researchers at the Japan Synchrotron Radiation Research Institute and the DOE’s Oak Ridge National Laboratory. Calculations were performed using resources of the DOE’s National Energy Research Scientific Computing Center (NERSC), and computer simulations used resources of the Oak Ridge Leadership Computing Facility. Major funding came from the European Research Council under the European Union’s Horizon 2020 research and innovation program and from the DOE Office of Science.

    LCLS, SSRL and NERSC are DOE Office of Science user facilities.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: