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  • richardmitnick 3:38 pm on January 3, 2019 Permalink | Reply
    Tags: , , , Electron spin, , SARPES detector, Spin-orbit coupling,   

    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 .

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    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.

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  • richardmitnick 1:26 pm on December 10, 2018 Permalink | Reply
    Tags: Australian scientists have investigated new directions to scale up qubits utilising their spin-orbit coupling adding a new suite of tools to the armory, Latest results revealed a previously unknown coupling of the electron spin to the electric fields typically found in device architectures created by control electrodes, , Spin-orbit coupling,   

    From University of New South Wales: “Harnessing the power of ‘spin-orbit’ coupling: scaling up spin-based quantum computation” 

    U NSW bloc

    From University of New South Wales

    10 Dec 2018
    Karen Viner-Smith

    Research teams from UNSW are investigating multiple pathways to scale up atom-based computing architectures using spin-orbit coupling – advancing towards their goal of building a silicon-based quantum computer in Australia.

    1
    Artist’s impression of spin-orbit coupling of atom qubits. Illustration: Tony Melov. Credit: CQC2T

    Australian scientists have investigated new directions to scale up qubits utilising their spin-orbit coupling, adding a new suite of tools to the armory.

    Spin-orbit coupling, the coupling of the qubits’ orbital and spin degree of freedom, allows the manipulation of the qubit via electric, rather than magnetic fields. Using the electric dipole coupling between qubits means they can be placed further apart, thereby providing flexibility in the chip fabrication process.

    In one of these approaches, published in Science Advances, a team of scientists led by UNSW Professor Sven Rogge investigated the spin-orbit coupling of a boron atom in silicon.

    “Single boron atoms in silicon are a relatively unexplored quantum system, but our research has shown that spin-orbit coupling provides many advantages for scaling up to a large number of qubits in quantum computing,” says Professor Rogge, Program Manager at the Centre for Quantum Computation and Communication Technology (CQC2T).

    Following on from earlier results from the UNSW team, published last month in Physical Review X, Rogge’s group has now focused on applying fast read-out of the spin state (1 or 0) of just two boron atoms in an extremely compact circuit all hosted in a commercial transistor.

    “Boron atoms in silicon couple efficiently to electric fields, enabling rapid qubit manipulation and qubit coupling over large distances. The electrical interaction also allows coupling to other quantum systems, opening up the prospects of hybrid quantum systems,” says Rogge.

    Phosphorus atom qubits

    Another piece of recent research by Prof Michelle Simmons’ team at UNSW has also highlighted the role of spin orbit coupling in atom-based qubits in silicon, this time with phosphorus atom qubits. The research was recently published in npj Quantum Information.

    The research revealed surprising results. For electrons in silicon — and in particular those bound to phosphorus donor qubits — spin orbit control was commonly regarded as weak, giving rise to seconds long spin lifetimes. However, the latest results revealed a previously unknown coupling of the electron spin to the electric fields typically found in device architectures created by control electrodes.

    “By careful alignment of the external magnetic field with the electric fields in an atomically engineered device, we found a means to extend these spin lifetimes to minutes,” says Professor Michelle Simmons, Director, CQC2T.

    “Given the long spin coherence times and the technological benefits of silicon, this newly discovered coupling of the donor spin with electric fields provides a pathway for electrically-driven spin resonance techniques, promising high qubit selectivity,” says Simmons.

    Both results highlight the benefits of understanding and controlling spin orbit coupling for large-scale quantum computing architectures.

    Commercialising silicon quantum computing IP in Australia

    Since May 2017, Australia’s first quantum computing company, Silicon Quantum Computing Pty Limited (SQC), has been working to create and commercialise a quantum computer based on a suite of intellectual property developed at the Australian Centre of Excellence for Quantum Computation and Communication Technology (CQC2T). Its goal is to produce a 10-qubit prototype device in silicon by 2022 as the forerunner to a commercial scale silicon-based quantum computer.

    As well as developing its own proprietary technology and intellectual property, SQC will continue to work with CQC2T and other participants in the Australian and International Quantum Computing ecosystems, to build and develop a silicon quantum computing industry in Australia and, ultimately, to bring its products and services to global markets.

    See the full article here .


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    U NSW Campus

    Welcome to UNSW Australia (The University of New South Wales), one of Australia’s leading research and teaching universities. At UNSW, we take pride in the broad range and high quality of our teaching programs. Our teaching gains strength and currency from our research activities, strong industry links and our international nature; UNSW has a strong regional and global engagement.

    In developing new ideas and promoting lasting knowledge we are creating an academic environment where outstanding students and scholars from around the world can be inspired to excel in their programs of study and research. Partnerships with both local and global communities allow UNSW to share knowledge, debate and research outcomes. UNSW’s public events include concert performances, open days and public forums on issues such as the environment, healthcare and global politics. We encourage you to explore the UNSW website so you can find out more about what we do.

     
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