Tagged: High-temperature superconductivity Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 9:47 am on December 8, 2017 Permalink | Reply
    Tags: , , , , High-temperature superconductivity, , RIXS-resonant inelastic x-ray scattering, Scientists found that as superconductivity vanishes at higher temperatures powerful waves of electrons begin to curiously uncouple and behave independently—like ocean waves splitting and rippling in, Superconductors carry electricity with perfect efficiency, The puzzling interplay between two key quantum properties of electrons: spin and charge   

    From BNL: “Breaking Electron Waves Provide New Clues to High-Temperature Superconductivity” 

    Brookhaven Lab

    December 5, 2017
    Justin Eure
    jeure@bnl.gov

    Scientists tracked elusive waves of charge and spin that precede and follow the mysterious emergence of superconductivity.

    1
    Brookhaven’s Robert Konik, Genda Gu, Mark Dean, and Hu Miao

    Superconductors carry electricity with perfect efficiency, unlike the inevitable waste inherent in traditional conductors like copper. But that perfection comes at the price of extreme cold—even so-called high-temperature superconductivity (HTS) only emerges well below zero degrees Fahrenheit. Discovering the ever-elusive mechanism behind HTS could revolutionize everything from regional power grids to wind turbines.

    Now, a collaboration led by the U.S. Department of Energy’s Brookhaven National Laboratory has discovered a surprising breakdown in the electron interactions that may underpin HTS. The scientists found that as superconductivity vanishes at higher temperatures, powerful waves of electrons begin to curiously uncouple and behave independently—like ocean waves splitting and rippling in different directions.

    “For the first time, we pinpointed these key electron interactions happening after superconductivity subsides,” said first author and Brookhaven Lab research associate Hu Miao. “The portrait is both stranger and more exciting than we expected, and it offers new ways to understand and potentially exploit these remarkable materials.”

    The new study, published November 7 in the journal PNAS, explores the puzzling interplay between two key quantum properties of electrons: spin and charge.

    “We know charge and spin lock together and form waves in copper-oxides cooled down to superconducting temperatures,” said study senior author and Brookhaven Lab physicist Mark Dean. “But we didn’t realize that these electron waves persist but seem to uncouple at higher temperatures.”

    Electronic stripes and waves

    2
    In the RIXS technique, intense x-rays deposit energy into the electron waves of atomically thin layers of high-temperature superconductors. The difference in x-ray energy before and after interaction reveals key information about the fundamental behavior of these exciting and mysterious materials.

    Scientists at Brookhaven Lab discovered in 1995 that spin and charge can lock together and form spatially modulated “stripes” at low temperatures in some HTS materials. Other materials, however, feature correlated electron charges rolling through as charge-density waves that appear to ignore spin entirely. Deepening the HTS mystery, charge and spin can also abandon independence and link together.

    “The role of these ‘stripes’ and correlated waves in high-temperature superconductivity is hotly debated,” Miao said. “Some elements may be essential or just a small piece of the larger puzzle. We needed a clearer picture of electron activity across temperatures, particularly the fleeting signals at warmer temperatures.”

    Imagine knowing the precise chemical structure of ice, for example, but having no idea what happens as it transforms into liquid or vapor. With these copper-oxide superconductors, or cuprates, there is comparable mystery, but hidden within much more complex materials. Still, the scientists essentially needed to take a freezing-cold sample and meticulously warm it to track exactly how its properties change.

    Subtle signals in custom-made materials

    The team turned to a well-established HTS material, lanthanum-barium copper-oxides (LBCO) known for strong stripe formations. Brookhaven Lab scientist Genda Gu painstakingly prepared the samples and customized the electron configurations.

    “We can’t have any structural abnormalities or errant atoms in these cuprates—they must be perfect,” Dean said. “Genda is among the best in the world at creating these materials, and we’re fortunate to have his talent so close at hand.”

    At low temperatures, the electron signals are powerful and easily detected, which is part of why their discovery happened decades ago. To tease out the more elusive signals at higher temperatures, the team needed unprecedented sensitivity.

    “We turned to the European Synchrotron Radiation Facility (ESRF) in France for the key experimental work,” Miao said.


    ESRF. Grenoble, France

    “Our colleagues operate a beamline that carefully tunes the x-ray energy to resonate with specific electrons and detect tiny changes in their behavior.”

    The team used a technique called resonant inelastic x-ray scattering (RIXS) to track position and charge of the electrons. A focused beam of x-rays strikes the material, deposits some energy, and then bounces off into detectors. Those scattered x-rays carry the signature of the electrons they hit along the way.

    As the temperature rose in the samples, causing superconductivity to fade, the coupled waves of charge and spin began to unlock and move independently.

    “This indicates that their coupling may bolster the stripe formation, or through some unknown mechanism empower high-temperature superconductivity,” Miao said. “It certainly warrants further exploration across other materials to see how prevalent this phenomenon is. It’s a key insight, certainly, but it’s too soon to say how it may unlock the HTS mechanism.”

    That further exploration will include additional HTS materials as well as other synchrotron facilities, notably Brookhaven Lab’s National Synchrotron Light Source II (NSLS-II), a DOE Office of Science User Facility.

    BNL NSLS-II

    BNL NSLS II

    “Using new beamlines at NSLS-II, we will have the freedom to rotate the sample and take advantage of significantly better energy resolution,” Dean said. “This will give us a more complete picture of electron correlations throughout the sample. There’s much more discovery to come.”

    Additional collaborators on the study include Yingying Peng, Giacomo Ghiringhelli, and Lucio Braicovich of the Politecnico di Milano, who contributed to the x-ray scattering, as well as José Lorenzana of the University of Rome, Götz Seibold of the Institute for Physics in Cottbus, Germany, and Robert Konik of Brookhaven Lab, who all contributed to the theory work.

    This research was funded by DOE’s Office of Science through Brookhaven Lab’s Center for Emergent Superconductivity.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    BNL Campus

    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 3:35 pm on June 9, 2017 Permalink | Reply
    Tags: , “Stripes” of electronic charge, Bad metals, , Cuprate superconductors, High-temperature superconductivity, Oak Ridge Lab’s Spallation Neutron Source,   

    From BNL: “Surprising Stripes in a “Bad Metal” Offer Clues to High-Temperature Superconductivity” 

    Brookhaven Lab

    June 5, 2017
    Justin Eure
    jeure@bnl.gov

    Scientists measure subtle electronic fluctuations that could help pinpoint the mechanism behind high-temperature superconductors.

    1
    Ruidan Zhong and John Tranquada

    High-temperature superconductivity offers perfect conveyance of electricity, but it does so at the price of extreme cold and an ever-elusive mechanism. If understood, scientists might push superconductivity into warmer temperatures and radically enhance power grids, consumer electronics, and more—but the puzzle has persisted for more than 30 years.

    Now, scientists have broken new ground by approaching from a counter-intuitive angle: probing so-called “bad metals” that conduct electricity poorly. The researchers found that “stripes” of electronic charge, which may play a key role in superconductivity, persist across surprisingly high temperatures, shape conductivity, and have direction-dependent properties.

    The results, which examined the model system of custom-grown nickel-oxide materials, were published online April 28 in the journal Physical Review Letters.

    “This is a step on the path to resolving the mechanism of high-temperature superconductivity and the complex role of charge stripes,” said Ruidan Zhong, lead author of the study and a PhD student at Stony Brook University. “We captured snapshots of dynamic stripes fluctuating in a liquid phase, where they have freedom to align and intermittently allow the flow of electricity.”

    The collaboration used the Spallation Neutron Source at the U.S. Department of Energy’s (DOE) Oak Ridge National Laboratory to measure the stripes.

    ORNL Spallation Neutron Source


    ORNL Spallation Neutron Source


    ORNL Spallation Neutron Source

    “We’ve been studying stripe ordering for two decades, and the Oak Ridge instruments are perfect for exploring new territory,” said coauthor John Tranquada, a physicist at DOE’s Brookhaven National Laboratory. “The signal we were looking for was very weak, and was buried in a jungle of much stronger signals—but we found it.”

    Bombarding a bit of alchemy

    For decades scientists have been able to take certain copper-oxide (cuprate) insulators—meaning they do not conduct electricity—and substitute atoms to tweak the electron content and then induce superconductivity at frigid temperatures. While stripes likely play an essential role, their presence and behavior across temperatures is particularly difficult to track.

    “In cuprate superconductors, we have learned how to detect charge stripes when they are pinned to the atomic lattice, but once they start to move, we lose sight of them,” Tranquada said. “So, instead of a superconducting compound of lanthanum, strontium, copper, and oxygen, we did a bit of alchemy to replace the copper with nickel.”

    In an elegant process led by study coauthor and Brookhaven scientist Genda Gu, the nickel-oxide—or nickelate—crystals were grown from a liquid phase without the use of any container. As they offered a similar structure to cuprates, but with stronger stripe ordering, the elusive charge stripes would be easier to spot, assuming the right tool could be found to peer inside.

    The team turned to the time-of-flight Hybrid Spectrometer (HYSPEC) at Oak Ridge Lab’s Spallation Neutron Source, a DOE Office of Science User Facility. The instrument—the product of a proposal first developed at Brookhaven—bombarded the nickelate sample with a beam of neutrons that then scatter off the atomic structure. By measuring the time it takes for the scattered neutrons to reach detectors, the scientists deduced the energy lost or gained—this in turn revealed the presence or absence of the stripes.

    Schools of electronic fish

    The neutron scattering results, which require intense computer processing, provided evidence of a so-called nematic phase in the nickelate.

    “Electronic nematic phases are driven by electron correlations that break the rotational symmetry of the material’s crystal lattice,” Zhong said. “In the nickelate, these wave-like, correlated stripes move through the material and directly impact conductivity.”

    As Tranquada explained, this can be visualized as schools of long, slender fish swimming through some sunken structure.

    “They move in tight, highly coordinated, and elusive packs,” Tranquada said. “Swimming with these fish in a parallel direction can be quite smooth, but swimming against that coordinated group in a perpendicular direction is challenging. This is a bit like the way current travels through our nickelate and interacts with the charge waves.”

    The precise way in which these persistent and curious charge stripes influence conductivity in the nickelates—and more importantly in the analogous superconducting cuprates—remains unclear.

    “We hope that this work offers new opportunities for theory and experiment to explore high temperature superconductivity,” Zhong said. “As we keep mapping these materials, the mechanism will eventually run out of places to hide.”

    The other authors on the study were Barry Winn of Oak Ridge National Lab and Dmitry Reznik of the University of Colorado, Boulder.

    This work was supported by DOE’s Office of Science.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    BNL Campus

    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

     
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: