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  • richardmitnick 9:58 am on July 23, 2021 Permalink | Reply
    Tags: "Understanding the Physics in New Metals", , , Correlated metals, , , , RIXS-resonant inelastic x-ray scattering, Strongly correlated materials are candidates for novel high-temperature superconductors., These materials could prove useful for practical applications in areas such as superconductivity; data processing; and quantum computers., Using inelastic resonant x-ray scattering to study quantum materials such as correlated metals.,   

    From DOE’s Brookhaven National Laboratory (US) and Paul Scherrer Institute [Paul Scherrer Institut] (CH) : “Understanding the Physics in New Metals” 

    From DOE’s Brookhaven National Laboratory (US)

    and

    Paul Scherrer Institute [Paul Scherrer Institut] (CH)

    July 19, 2021

    Barbara Vonarburg, Paul Scherrer Institute

    1
    Brookhaven Lab Scientist Jonathan Pelliciari now works as a beamline scientist at the National Synchrotron Light Source II (NSLS-II)[below], where he continues to use inelastic resonant x-ray scattering to study quantum materials such as correlated metals.

    Researchers from the Paul Scherrer Institute PSI and the Brookhaven National Laboratory (BNL), working in an international team, have developed a new method for complex X-ray studies that will aid in better understanding so-called correlated metals. These materials could prove useful for practical applications in areas such as superconductivity; data processing; and quantum computers. Today the researchers present their work in the journal Physical Review X.

    In substances such as silicon or aluminium, the mutual repulsion of electrons hardly affects the material properties. Not so with so-called correlated materials, in which the electrons interact strongly with one another. The movement of one electron in a correlated material leads to a complex and coordinated reaction of the other electrons. It is precisely such coupled processes that make these correlated materials so promising for practical applications, and at the same time so complicated to understand.

    Strongly correlated materials are candidates for novel high-temperature superconductors, which can conduct electricity without loss and which are used in medicine, for example, in magnetic resonance imaging. They also could be used to build electronic components, or even quantum computers, with which data can be more efficiently processed and stored.

    “Strongly correlated materials exhibit a wealth of fascinating phenomena,” says Thorsten Schmitt, head of the Spectroscopy of Novel Materials Group at PSI: “However, it remains a major challenge to understand and exploit the complex behaviour that lies behind these phenomena.” Schmitt and his research group tackle this task with the help of a method for which they use the intense and extremely precise X-ray radiation from the Swiss Light Source SLS at PSI.

    4
    Swiss Light Source SLS Paul Scherrer Institut (PSI)

    This modern technique, which has been further developed at PSI in recent years, is called resonant inelastic X-ray scattering, or RIXS for short.

    2
    Thorsten Schmitt at the experiment station of the Swiss Light Source SLS, which provided the X-ray light used for the experiments. Credit: Mahir Dzambegovic/Paul Scherrer Institute.

    X-rays excite electrons

    With RIXS, soft X-rays are scattered off a sample. The incident X-ray beam is tuned in such a way that it elevates electrons from a lower electron orbital to a higher orbital, which means that special resonances are excited. This throws the system out of balance. Various electrodynamic processes lead it back to the ground state. Some of the excess energy is emitted again as X-ray light. The spectrum of this inelastically scattered radiation provides information about the underlying processes and thus on the electronic structure of the material.

    “In recent years, RIXS has developed into a powerful experimental tool for deciphering the complexity of correlated materials,” Schmitt explains. When used to investigate correlated insulators in particular, it works very well. Up to now, however, the method has been unsuccessful in probing correlated metals. Its failure was due to the difficulty of interpreting the extremely complicated spectra caused by many different electrodynamic processes during the scattering. “In this connection collaboration with theorists is essential,” explains Schmitt, “because they can simulate the processes observed in the experiment.”

    Calculations of correlated metals

    This is a specialty of theoretical physicist Keith Gilmore, formerly of the Brookhaven National Laboratory (BNL) in the USA and now at the Humboldt University of Berlin [Humboldt-Universität zu Berlin] (DE). “Calculating the RIXS results for correlated metals is difficult because you have to handle several electron orbitals, large bandwidths, and a large number of electronic interactions at the same time,” says Gilmore. Correlated insulators are easier to handle because fewer orbitals are involved; this allows model calculations that explicitly include all electrons. To be precise, Gilmore explains: “In our new method of describing the RIXS processes, we are now combining the contributions that come from the excitation of one electron with the coordinated reaction of all other electrons.”

    To test the calculation, the PSI researchers experimented with a substance that BNL scientist Jonathan Pelliciari had investigated in detail as part of his doctoral thesis at PSI: barium-iron-arsenide. If you add a specific amount of potassium atoms to the material, it becomes superconducting. It belongs to a class of unconventional high-temperature iron-based superconductors that are expected to provide a better understanding of the phenomenon. “Until now, the interpretation of RIXS measurements on such complex materials has been guided mainly by intuition. Now these RIXS calculations give us experimenters a framework that enables a more practical interpretation of the results. Our RIXS measurements at PSI on barium-iron-arsenide are in excellent agreement with the calculated profiles,” Pelliciari says.

    Combination of experiment and theory

    In their experiments, the researchers investigated the physics around the iron atom. “One advantage of RIXS is that you can concentrate on a specific component and examine it in detail for materials that consist of several elements,” Schmitt says. The well-tuned X-ray beam causes an inner electron in the iron atom to be elevated from the ground state in the core level to the higher energy valence band, which is only partially occupied. This initial excitation of the core electron can cause further secondary excitations and trigger many complicated decay processes that ultimately manifest themselves in spectral satellite structures. (See graphic.)

    3
    The graphic shows how an electron (blue dot) can be elevated to different energy levels (dotted arrows) or falls back to lower energy levels. Between the highest energy level and somewhat lower level, secondary processes take place. The curve in the background represents the iron electronic levels.
    Credit: Keith Gilmore/Paul Scherrer Institute.

    Since the contributions of the many reactions are sometimes small and close to one another, it is difficult to find out which processes actually took place in the experiment. Here the combination of experiment and theory helps. “If you have no theoretical support for difficult experiments, you cannot understand the processes, that is, the physics, in detail,” Schmitt says. The same also applies to theory: “You often don’t know which theories are realistic until you can compare them with an experiment. Progress in understanding comes when experiment and theory are brought together. This descriptive method thus has the potential to become a reference for the interpretation of spectroscopic experiments on correlated metals.”

    See the full article here .


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    The Paul Scherrer Institute [Paul Scherrer Institut] (CH) is the largest research institute for natural and engineering sciences within Switzerland. We perform world-class research in three main subject areas: Matter and Material; Energy and the Environment; and Human Health. By conducting fundamental and applied research, we work on long-term solutions for major challenges facing society, industry and science.

    The Paul Scherrer Institute (PSI) is a multi-disciplinary research institute for natural and engineering sciences in Switzerland. It is located in the Canton of Aargau in the municipalities Villigen and Würenlingen on either side of the River Aare, and covers an area over 35 hectares in size. Like Swiss Federal Institute of Technology ETH Zürich [Eidgenössische Technische Hochschule Zürich)](CH) and EPFL (Swiss Federal Institute of Technology in Lausanne) [École polytechnique fédérale de Lausanne](CH), PSI belongs to the Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles polytechniques fédérales](CH). The PSI employs around 2100 people. It conducts basic and applied research in the fields of matter and materials, human health, and energy and the environment. About 37% of PSI’s research activities focus on material sciences, 24% on life sciences, 19% on general energy, 11% on nuclear energy and safety, and 9% on particle physics.

    PSI develops, builds and operates large and complex research facilities and makes them available to the national and international scientific communities. In 2017, for example, more than 2500 researchers from 60 different countries came to PSI to take advantage of the concentration of large-scale research facilities in the same location, which is unique worldwide. About 1900 experiments are conducted each year at the approximately 40 measuring stations in these facilities.

    In recent years, the institute has been one of the largest recipients of money from the Swiss lottery fund.

    Research and specialist areas

    PSI develops, builds and operates several accelerator facilities, e. g. a 590 MeV high-current cyclotron, which in normal operation supplies a beam current of about 2.2 mA. PSI also operates four large-scale research facilities: a synchrotron light source (SLS), which is particularly brilliant and stable, a spallation neutron source (SINQ), a muon source (SμS) and an X-ray free-electron laser (SwissFEL). This makes PSI currently (2020) the only institute in the world to provide the four most important probes for researching the structure and dynamics of condensed matter (neutrons, muons and synchrotron radiation) on a campus for the international user community. In addition, HIPA’s target facilities also produce pions that feed the muon source and the Ultracold Neutron source UCN produces very slow, ultracold neutrons. All these particle types are used for research in particle physics.

    One of ten national laboratories overseen and primarily funded by the DOE(US) Office of Science, DOE’s Brookhaven National Laboratory (US) 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(US), the largest academic user of Laboratory facilities, and Battelle(US), a nonprofit, applied science and technology organization.

    Research at BNL specializes in nuclear and high energy physics, energy science and technology, environmental and bioscience, nanoscience and national security. The 5,300 acre campus contains several large research facilities, including the Relativistic Heavy Ion Collider [below] and National Synchrotron Light Source II [below]. Seven Nobel prizes have been awarded for work conducted at Brookhaven lab.

    BNL is staffed by approximately 2,750 scientists, engineers, technicians, and support personnel, and hosts 4,000 guest investigators every year. The laboratory has its own police station, fire department, and ZIP code (11973). In total, the lab spans a 5,265-acre (21 km^2) area that is mostly coterminous with the hamlet of Upton, New York. BNL is served by a rail spur operated as-needed by the New York and Atlantic Railway. Co-located with the laboratory is the Upton, New York, forecast office of the National Weather Service.

    Major programs

    Although originally conceived as a nuclear research facility, Brookhaven Lab’s mission has greatly expanded. Its foci are now:

    Nuclear and high-energy physics
    Physics and chemistry of materials
    Environmental and climate research
    Nanomaterials
    Energy research
    Nonproliferation
    Structural biology
    Accelerator physics

    Operation

    Brookhaven National Lab was originally owned by the Atomic Energy Commission(US) and is now owned by that agency’s successor, the United States Department of Energy (DOE). DOE subcontracts the research and operation to universities and research organizations. It is currently operated by Brookhaven Science Associates LLC, which is an equal partnership of Stony Brook University(US) and Battelle Memorial Institute(US). From 1947 to 1998, it was operated by Associated Universities, Inc. (AUI) (US), but AUI lost its contract in the wake of two incidents: a 1994 fire at the facility’s high-beam flux reactor that exposed several workers to radiation and reports in 1997 of a tritium leak into the groundwater of the Long Island Central Pine Barrens on which the facility sits.

    Foundations

    Following World War II, the US Atomic Energy Commission was created to support government-sponsored peacetime research on atomic energy. The effort to build a nuclear reactor in the American northeast was fostered largely by physicists Isidor Isaac Rabi and Norman Foster Ramsey Jr., who during the war witnessed many of their colleagues at Columbia University leave for new remote research sites following the departure of the Manhattan Project from its campus. Their effort to house this reactor near New York City was rivalled by a similar effort at the Massachusetts Institute of Technology (US) to have a facility near Boston, Massachusettes(US). Involvement was quickly solicited from representatives of northeastern universities to the south and west of New York City such that this city would be at their geographic center. In March 1946 a nonprofit corporation was established that consisted of representatives from nine major research universities — Columbia University(US), Cornell University(US), Harvard University(US), Johns Hopkins University(US), Massachusetts Institute of Technology(US), Princeton University(US), University of Pennsylvania(US), University of Rochester(US), and Yale University(US).

    Out of 17 considered sites in the Boston-Washington corridor, Camp Upton on Long Island was eventually chosen as the most suitable in consideration of space, transportation, and availability. The camp had been a training center from the US Army during both World War I and World War II. After the latter war, Camp Upton was deemed no longer necessary and became available for reuse. A plan was conceived to convert the military camp into a research facility.

    On March 21, 1947, the Camp Upton site was officially transferred from the U.S. War Department to the new U.S. Atomic Energy Commission (AEC), predecessor to the U.S. Department of Energy (DOE).

    Research and facilities

    Reactor history

    In 1947 construction began on the first nuclear reactor at Brookhaven, the Brookhaven Graphite Research Reactor. This reactor, which opened in 1950, was the first reactor to be constructed in the United States after World War II. The High Flux Beam Reactor operated from 1965 to 1999. In 1959 Brookhaven built the first US reactor specifically tailored to medical research, the Brookhaven Medical Research Reactor, which operated until 2000.

    Accelerator history

    In 1952 Brookhaven began using its first particle accelerator, the Cosmotron. At the time the Cosmotron was the world’s highest energy accelerator, being the first to impart more than 1 GeV of energy to a particle.


    The Cosmotron was retired in 1966, after it was superseded in 1960 by the new Alternating Gradient Synchrotron (AGS).

    The AGS was used in research that resulted in 3 Nobel prizes, including the discovery of the muon neutrino, the charm quark, and CP violation.

    In 1970 in BNL started the ISABELLE project to develop and build two proton intersecting storage rings.

    The groundbreaking for the project was in October 1978. In 1981, with the tunnel for the accelerator already excavated, problems with the superconducting magnets needed for the ISABELLE accelerator brought the project to a halt, and the project was eventually cancelled in 1983.

    The National Synchrotron Light Source (US) operated from 1982 to 2014 and was involved with two Nobel Prize-winning discoveries. It has since been replaced by the National Synchrotron Light Source II (US) [below].

    After ISABELLE’S cancellation, physicist at BNL proposed that the excavated tunnel and parts of the magnet assembly be used in another accelerator. In 1984 the first proposal for the accelerator now known as the Relativistic Heavy Ion Collider (RHIC)[below] was put forward. The construction got funded in 1991 and RHIC has been operational since 2000. One of the world’s only two operating heavy-ion colliders, RHIC is as of 2010 the second-highest-energy collider after the Large Hadron Collider(CH). RHIC is housed in a tunnel 2.4 miles (3.9 km) long and is visible from space.

    On January 9, 2020, It was announced by Paul Dabbar, undersecretary of the US Department of Energy Office of Science, that the BNL eRHIC design has been selected over the conceptual design put forward by DOE’s Thomas Jefferson National Accelerator Facility [Jlab] (US) as the future Electron–ion collider (EIC) in the United States.

    In addition to the site selection, it was announced that the BNL EIC had acquired CD-0 (mission need) from the Department of Energy. BNL’s eRHIC design proposes upgrading the existing Relativistic Heavy Ion Collider, which collides beams light to heavy ions including polarized protons, with a polarized electron facility, to be housed in the same tunnel.

    Other discoveries

    In 1958, Brookhaven scientists created one of the world’s first video games, Tennis for Two. In 1968 Brookhaven scientists patented Maglev, a transportation technology that utilizes magnetic levitation.

    Major facilities

    Relativistic Heavy Ion Collider (RHIC), which was designed to research quark–gluon plasma and the sources of proton spin. Until 2009 it was the world’s most powerful heavy ion collider. It is the only collider of spin-polarized protons.
    Center for Functional Nanomaterials (CFN), used for the study of nanoscale materials.
    BNL National Synchrotron Light Source II(US), Brookhaven’s newest user facility, opened in 2015 to replace the National Synchrotron Light Source (NSLS), which had operated for 30 years.[19] NSLS was involved in the work that won the 2003 and 2009 Nobel Prize in Chemistry.
    Alternating Gradient Synchrotron, a particle accelerator that was used in three of the lab’s Nobel prizes.
    Accelerator Test Facility, generates, accelerates and monitors particle beams.
    Tandem Van de Graaff, once the world’s largest electrostatic accelerator.
    Computational Science resources, including access to a massively parallel Blue Gene series supercomputer that is among the fastest in the world for scientific research, run jointly by Brookhaven National Laboratory and Stony Brook University.
    Interdisciplinary Science Building, with unique laboratories for studying high-temperature superconductors and other materials important for addressing energy challenges.
    NASA Space Radiation Laboratory, where scientists use beams of ions to simulate cosmic rays and assess the risks of space radiation to human space travelers and equipment.

    Off-site contributions

    It is a contributing partner to ATLAS experiment, one of the four detectors located at the Large Hadron Collider (LHC).


    It is currently operating at CERN near Geneva, Switzerland.

    Brookhaven was also responsible for the design of the SNS accumulator ring in partnership with Spallation Neutron Source at DOE’s Oak Ridge National Laboratory (US), Tennessee.

    Brookhaven plays a role in a range of neutrino research projects around the world, including the Daya Bay Neutrino Experiment (CN) nuclear power plant, approximately 52 kilometers northeast of Hong Kong and 45 kilometers east of Shenzhen, China.


     
  • richardmitnick 1:45 pm on November 3, 2020 Permalink | Reply
    Tags: "A New Approach for Studying Electric Charge Arrangements in a Superconductor", , Cuperates, , Doping with LSCO- lanthanum strontium copper and oxygen., RIXS-resonant inelastic x-ray scattering   

    From DOE’s Brookhaven National Laboratory: “A New Approach for Studying Electric Charge Arrangements in a Superconductor” 

    From DOE’s Brookhaven National Laboratory

    November 3, 2020
    Laura Mgrdichian
    mgrdichian@gmail.com

    1
    Brookhaven Lab scientist Mark Dean used the Soft Inelastic X-Ray (SIX) beamline at the National Synchrotron Light Source II (NSLS-II) to unveil new insights about a cuperates, a particular group of high-temperature superconductors.

    High-temperature superconductors are a class of materials that can conduct electricity with almost zero resistance at temperatures that are relatively high compared to their standard counterparts, which must be chilled to nearly absolute zero—the coldest temperature possible. The high-temperature materials are exciting because they hold the possibility of revolutionizing modern life, such as by facilitating ultra-efficient energy transmission or being used to create cutting-edge quantum computers.

    One particular group of high-temperature superconductors, the cuprates, has been studied for 30 years, yet scientists still cannot fully explain how they work: What goes on inside a “typical” cuprate?

    Piecing together a complete picture of their electronic behavior is vital to engineering the “holy grail” of cuprates: a versatile, robust material that can superconduct at room temperature and ambient pressure.

    To that end, a research group led by scientists from the U.S. Department of Energy’s (DOE’s) Brookhaven National Laboratory recently discovered new information about the electronic behavior of a particular cuprate using an x-ray technique that has not—until now—been widely used to study them. Working in part at Brookhaven Lab’s National Synchrotron Light Source II (NSLS-II), a DOE Office of Science User Facility, the researchers used a form of x-ray scattering to investigate a specific arrangement of electric charge that arises in cuprates: an ordered pattern of electrons known as a charge-density wave (CDW).

    The x-ray technique—resonant inelastic x-ray scattering (RIXS)—may open up intriguing new avenues of research into these materials. The results of this investigation are published in the May 21 online edition of Physical Review Letters.

    CDWs in the cuprates

    A CDW can be visualized as a standing-wave pattern of electrons. CDWs arise in ordered, crystalline materials, such as cuprates, which are composed of alternating layers of copper oxide and an insulator (typically another oxide). The insulating planes serve as charge reservoirs that feed the copper oxide layers where the superconductivity takes place.

    CDWs have long been suspected to play a vital role in how the cuprates superconduct, but characterizing one—how it emerges and disappears, how it behaves, how it adds to or impedes superconductivity—is an ongoing challenge for scientists.

    At NSLS-II and the United Kingdom’s Diamond Light Source, the group studied a cuprate composed of lanthanum, copper, and oxygen that was “doped” with small amounts of strontium (dubbed LSCO).

    Diamond Light Source, located at the Harwell Science and Innovation Campus in Oxfordshire U.K.

    Harwell Science and Innovation campus, Oxfordshire (UK).

    Doping is a technique in which tiny amounts of an impurity substance are added to a compound to alter or improve its electrical, optical, or structural properties.

    The group created four LSCO samples with four different doping levels. The doping levels cover a range of electronic behavior in which the CDW is at its strongest and then disappears. This range also covers a transition in the electronic structure of LSCO: the “Fermi surface,” which is a theoretical 3-D shell that separates the filled and unfilled electron orbitals—the volume around a nucleus where particular electrons are most likely to be—when the material has a temperature of absolute zero. Fermi surfaces are abstract, but they are very important, often predicting a material’s electronic behavior as well as many other properties.

    A new way to study cuprate CDWs

    In RIXS, the energy of incident x-ray photons is transferred to core-level electrons in a crystalline sample, “exciting” them into the conduction band. The vacancies left by the core electrons are filled by valence-band electrons, which emit a photon as they make the jump to the lower-energy band. Those emitted photons form a spectrum of energies that can be analyzed to gain information about the excitations and the material’s overall electronic behavior.

    At NSLS-II, the work was done at the Soft Inelastic X-Ray (SIX) beamline, which offers ultra-high energy resolution RIXS. The technique has an enhanced sensitivity to excitations of both valence electrons and phonons—the collective vibrations of the atomic lattice. A CDW can be associated with these excitations.

    “The recent discovery that CDW effects are weaved into cuprate RIXS spectra has been exciting for researchers in this field, as it holds the tantalizing promise that we may be able to clarify the interactions that give rise to CDWs,” said Mark Dean, a physicist in Brookhaven’s Condensed Matter Physics and Materials Science Department, who led the study together with Xuerong Liu from Shanghai Tech University and Valentina Bisogni from NSLS-II.

    1
    Brookhaven Lab scientist Valentina Bisogni shows how to load samples in to the chamber of the Soft Inelastic X-Ray (SIX) beamline at the National Synchrotron Light Source II (NSLS-II).

    Dean and his colleagues found that the RIXS spectra are mostly unchanged at all doping levels, despite crossing the Fermi transition. This indicates that the spectra are not related to excitations near the Fermi surface. But learning more from the RIXS spectra—namely, isolating and interpreting the possible effects of a CDW—is a challenge.

    “CDWs inevitably modify their host crystal lattice and thus the phonons,” said Bisogni. “Further complicating things is the fact that there are different approaches to interpreting RIXS data.”

    Through rigorous, careful analysis, the research team concluded that the RIXS spectra have little or no direct relationship to electronic excitations. Instead, they are most powerfully affected by phonon behavior, including a “softening” of the phonons—a reduction in frequency—induced by the CDW and changes in the intensity of the phonons.

    “The world-record energy resolution recently achieved at the SIX beamline was crucial to this investigation, allowing us to resolve and identify the different contributions present in the RIXS data,” said Dean.

    The group states that their results support a scenario in which the CDW is driven by “strong correlations” between electrons—a term used to describe not-well-understood electronic behaviors in materials—and add support to the idea that the RIXS response in the cuprates is driven by how the CDW modifies the crystal lattice, and how those modifications invoke more complex interactions.

    “Thanks to the performance of SIX, we were able to place a new piece in the puzzle that is the physics of the cuprate superconductors,” said Bisogni. “After all the work getting the beamline built, commissioned, and optimized, it is great to see high-impact science coming out of that effort. We hope that this publication will be the first of many such collaborative publications.”

    In future work, the same team hope to study these systems with even higher energy resolution to reveal details of the lattice’s lower energy vibrational modes.

    Brookhaven National Laboratory is supported by the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.

    See the full article here .


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    Brookhaven Campus.


    BNL Center for Functional Nanomaterials.

    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.

     
  • richardmitnick 8:28 am on August 18, 2019 Permalink | Reply
    Tags: , , , , , RIXS-resonant inelastic x-ray scattering, , SSRL-Stanford Synchrotron Light Source, ,   

    From SLAC National Accelerator Lab: “Scientists report two advances in understanding the role of ‘charge stripes’ in superconducting materials” 

    From SLAC National Accelerator Lab

    Ali Sundermier
    Glennda Chui

    The studies could lead to a new understanding of how high-temperature superconductors operate.

    High-temperature superconductors, which carry electricity with zero resistance at much higher temperatures than conventional superconducting materials, have generated a lot of excitement since their discovery more than 30 years ago because of their potential for revolutionizing technologies such as maglev trains and long-distance power lines. But scientists still don’t understand how they work.

    One piece of the puzzle is the fact that charge density waves – static stripes of higher and lower electron density running through a material – have been found in one of the major families of high-temperature superconductors, the copper-based cuprates. But do these charge stripes enhance superconductivity, suppress it or play some other role?

    In independent studies, two research teams report important advances in understanding how charge stripes might interact with superconductivity. Both studies were carried out with X-rays at the Department of Energy’s SLAC National Accelerator Laboratory.

    Exquisite detail

    In a paper published today in Science Advances, researchers from the University of Illinois at Urbana-Champaign (UIUC) used SLAC’s Linac Coherent Light Source (LCLS) X-ray free-electron laser [below] to observe fluctuations in charge density waves in a cuprate superconductor.

    1
    This cutaway view shows stripes of higher and lower electron density – “charge stripes” – within a copper-based superconducting material. Experiments with SLAC’s X-ray laser directly observed how those stripes fluctuate when hit with a pulse of light, a step toward understanding how they interact with high-temperature superconductivity. (Greg Stewart/SLAC National Accelerator Laboratory)

    They disturbed the charge density waves with pulses from a conventional laser and then used RIXS, or resonant inelastic X-ray scattering, to watch the waves recover over a period of a few trillionths of a second. This recovery process behaved according to a universal dynamical scaling law: It was the same at all scales, much as a fractal pattern looks the same whether you zoom in or zoom out.

    With LCLS, the scientists were able to measure, for the first time and in exquisite detail, exactly how far and how fast the charge density waves fluctuated. To their surprise, the team discovered that the fluctuations were not like the ringing of a bell or the bouncing of a trampoline; instead, they were more like the slow diffusion of a syrup – a quantum analog of liquid crystal behavior, which had never been seen before in a solid.

    “Our experiments at LCLS establish a new way to study fluctuations in charge density waves, which could lead to a new understanding of how high-temperature superconductors operate,” says Matteo Mitrano, a postdoctoral researcher in professor Peter Abbamonte’s group at UIUC.

    This team also included researchers from Stanford University, the National Institute of Standards and Technology and Brookhaven National Laboratory.

    Hidden arrangements

    Another study, reported last month in Nature Communications, used X-rays from SLAC’S Stanford Synchrotron Radiation Lightsource (SSRL) to discover two types of charge density wave arrangements, making a new link between these waves and high-temperature superconductivity.

    SLAC/SSRL

    Led by SLAC scientist Jun-Sik Lee, the research team used RSXS, or resonant soft X-ray scattering, to watch how temperature affected the charge density waves in a cuprate superconductor.

    “This resolves a mismatch in data from previous experiments and charts a new course for fully mapping the behaviors of electrons in these exotic superconducting materials,” Lee says.

    “I believe that exploring new or hidden arrangements, as well as their intertwining phenomena, will contribute to our understanding of high-temperature superconductivity in cuprates, which will inform researchers in their quest to design and develop new superconductors that work at warmer temperatures.”

    The team also included researchers from Stanford, Pohang Accelerator Laboratory in South Korea and Tohoku University in Japan.

    SSRL and LCLS are DOE Office of Science user facilities. Both studies were supported by the Office of Science.

    See the full article here .


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    SLAC/LCLS


    SLAC/LCLS II projected view


    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.

     
  • richardmitnick 9:47 am on December 8, 2017 Permalink | Reply
    Tags: , , , , , , 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 .

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