• Magnetism helps electrons vanish in high

    From ScienceDaily@1:317/3 to All on Thu Mar 10 21:30:40 2022
    Magnetism helps electrons vanish in high-temp superconductors

    Date:
    March 10, 2022
    Source:
    Cornell University
    Summary:
    A physicist's discovery could lead to the engineering of high-temp
    superconducting properties into materials useful for quantum
    computing, medical imaging.



    FULL STORY ========================================================================== Superconductors -- metals in which electricity flows without resistance
    -- hold promise as the defining material of the near future, according to physicist Brad Ramshaw, and are already used in medical imaging machines,
    drug discovery research and quantum computers being built by Google
    and IBM.


    ========================================================================== However, the super-low temperatures conventional superconductors need to function -- a few degrees above absolute zero -- make them too expensive
    for wide use.

    In their quest to find more useful superconductors, Ramshaw, the Dick &
    Dale Reis Johnson Assistant Professor of physics in the College of Arts
    and Sciences (A&S), and colleagues have discovered that magnetism is
    key to understanding the behavior of electrons in "high-temperature" superconductors. With this finding, they've solved a 30-year-old mystery surrounding this class of superconductors, which function at much higher temperatures, greater than 100 degrees above absolute zero. Their paper,
    "Fermi Surface Transformation at the Pseudogap Critical Point of a
    Cuprate Superconductor," published in Nature Physics March 10.

    "We'd like to understand what makes these high-temperature superconductors
    work and engineer that property into some other material that is easier
    to adopt in technologies," Ramshaw said.

    A central mystery to high-temperature superconductors is what happens
    with their electrons, Ramshaw said.

    "All metals have electrons, and when a metal becomes a superconductor,
    the electrons pair up with each other," he said. "We measure something
    called the 'Fermi surface,' which you can think of as a map showing
    where all the electrons are in a metal." To study how electrons pair
    up in high-temperature superconductors, researchers continuously change
    the number of electrons through a process known as chemical doping. In high-temperature superconductors, at a certain "critical point," electrons
    seem to vanish from the Fermi surface map, Ramshaw said.



    ==========================================================================
    The researchers zeroed in on this critical point to figure out what
    makes the electrons vanish, and where they go. They used the strongest steady-state magnet in the world, the 45-tesla hybrid magnet at the
    National High Magnetic Field Laboratory in Tallahassee, Florida,
    to measure the Fermi surface of a copper-oxide high temperature
    superconductor as a function of electron concentration, right around
    the critical point.

    They found that the Fermi surface changes completely as researchers dial
    past the critical point.

    "It's as if you were looking at a real map and all of a sudden most of the continents just disappeared," Ramshaw said. "That's what we found happens
    to the Fermi surface of high-temperature superconductors at the critical
    point - - most of the electrons in a particular region, a particular
    part of the map, vanish." It was important for the researchers to note
    not just that electrons were vanishing, but which ones in particular,
    Ramshaw said.

    They built different simulation models based on several theories and
    tested whether they could explain the data, said Yawen Fang, doctoral
    student in physics and lead author of the paper.



    ==========================================================================
    "In the end, we have a winning model, which is the one associated
    with magnetism," Fang said. "We are stepping confidently from the well-understood side of the material, benchmarking our technique, into
    the mysterious side past the critical point." Now that they know which electrons vanish, the researchers have an idea why - - it has to do
    with magnetism.

    "There have always been hints that magnetism and superconductivity are
    related in high-temperature superconductors, and our work shows that
    this magnetism seems to appear right at the critical point and gobble up
    most of the electrons," Ramshaw said. "This critical point also marks
    the electron concentration where the superconductivity happens at the
    highest temperatures, and higher-temperature superconductors are the
    goal here." Knowing that the critical point is associated with magnetism offers insight into why these particular superconductors have such high transition temperatures, Ramshaw said, and maybe even where to look to
    find new ones with even higher transition temperatures.

    "It is a 30-year-old debate that precedes our study, and we came up with
    a straightforward answer," said Gae"l Grissonnanche, a postdoctoral
    fellow with the Kavli Institute at Cornell for Nanoscale Science and
    co-first author.

    This research was supported in part by the National Science Foundation,
    the Canadian Institute for Advanced Research Azrieli Global Scholars
    Program, and the Kavli Institute for Nanoscale Science at Cornell.


    ========================================================================== Story Source: Materials provided by Cornell_University. Original written
    by Kate Blackwood, courtesy of the Cornell Chronicle. Note: Content may
    be edited for style and length.


    ========================================================================== Journal Reference:
    1. Yawen Fang, Gae"l Grissonnanche, Anae"lle Legros, Simon Verret,
    Francis
    Laliberte', Cle'ment Collignon, Amirreza Ataei, Maxime Dion,
    Jianshi Zhou, David Graf, Michael J. Lawler, Paul A. Goddard,
    Louis Taillefer, B.

    J. Ramshaw. Fermi surface transformation at the pseudogap critical
    point of a cuprate superconductor. Nature Physics, 2022; DOI:
    10.1038/s41567- 022-01514-1 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/03/220310143715.htm

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