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  • richardmitnick 2:29 pm on February 15, 2021 Permalink | Reply
    Tags: "Kagome graphene promises exciting properties", A graphene compound made of carbon atoms and a few nitrogen atoms that form a regular lattice of hexagons and triangles., , , , Kagome graphene, , Scanning tunneling microscopy, Swiss Nanoscience Institute [Schweizerisches Institut für Nanowissenschaften][CH], The researchers' measurements have delivered promising results that point to unusual electrical or magnetic properties., The so-called Kagome lattice behaves like a semiconductor and could also have unusual electrical properties., This behavior clearly distinguishes the material from conventional graphene., University of Basel [Universität Basel] (CH),   

    From University of Basel [Universität Basel] (CH) and U Bern [Universität Bern] (CH): “Kagome graphene promises exciting properties” 

    u-basel-bloc

    From University of Basel [Universität Basel] (CH)

    and

    From U Bern [Universität Bern] (CH)

    1
    Kagome graphene is characterized by a regular lattice of hexagons and triangles. It behaves as a semiconductor and may also have unusual electrical properties. Credit: R. Pawlak, Department of Physics, University of Basel [Universität Basel] (CH).

    Researchers around the world are searching for new synthetic materials with special properties like superconductivity—that is, the conduction of electric current without resistance. These new substances are an important step in the development of highly energy-efficient electronics. The starting material is often a single-layer honeycomb structure of carbon atoms (graphene).

    Theoretical calculations predict that the compound known as kagome graphene should have completely different properties to graphene. Kagome graphene consists of a regular pattern of hexagons and equilateral triangles that surround one another. The name kagome comes from the old Japanese art of kagome weaving, in which baskets are woven in the same pattern.

    Kagome lattice with new properties

    Researchers from the Department of Physics and the Swiss Nanoscience Institute [Schweizerisches Institut für Nanowissenschaften][CH] at the University of Basel [Universität Basel] (CH), working in collaboration with the University of Bern [Universität Bern](CH), have now produced and studied kagome graphene for the first time, as they report in the journal Angewandte Chemie. The researchers’ measurements have delivered promising results that point to unusual electrical or magnetic properties.

    To produce the kagome graphene, the team applied a precursor to a silver substrate by vapor deposition and then heated it to form an organometallic intermediate on the metal surface. Further heating produced kagome graphene, which is made up exclusively of carbon and nitrogen atoms and features the same regular pattern of hexagons and triangles.


    Kagome Graphene. Physicists of the University of Basel [Universität Basel] (CH) have for the first time produced a graphene compound made of carbon atoms and a few nitrogen atoms that form a regular lattice of hexagons and triangles. This honeycomb-shaped, so-called Kagome lattice behaves like a semiconductor and could also have unusual electrical properties. In the future, it may be used in electronic sensors or quantum computers. Credit: Swiss Nanoscience Institute [Schweizerisches Institut für Nanowissenschaften] [CH].

    Strong interactions between electrons

    “We used scanning tunneling and atomic force microscopes to study the structural and electronic properties of the kagome lattice,” reports Dr. Rémy Pawlak, first author of the study. With microscopes of this kind, researchers can probe the structural and electrical properties of materials using a tiny tip—in this case, the tip was terminated with individual carbon monoxide molecules.

    In doing so, the researchers observed that electrons of a defined energy, which is selected by applying an electrical voltage, are “trapped” between the triangles that appear in the crystal lattice of kagome graphene. This behavior clearly distinguishes the material from conventional graphene, where electrons are distributed across various energy states in the lattice—in other words, they are delocalized.

    “The localization observed in kagome graphene is desirable and precisely what we were looking for,” explains Professor Ernst Meyer, who leads the group in which the projects were carried out. “It causes strong interactions between the electrons—and, in turn, these interactions provide the basis for unusual phenomena, such as conduction without resistance.”

    Further investigations planned

    The analyses also revealed that kagome graphene features semiconducting properties—in other words, its conducting properties can be switched on or off, as with a transistor. In this way, kagome graphene differs significantly from graphene, whose conductivity cannot be switched on and off as easily.

    In subsequent investigations, the team will detach the kagome lattice from its metallic substrate and study its electronic properties further. “The flat band structure identified in the experiments supports the theoretical calculations, which predict that exciting electronic and magnetic phenomena could occur in kagome lattices. In the future, kagome graphene could act as a key building block in sustainable and efficient electronic components,” says Ernst Meyer.

    See the full article here .

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    Please help promote STEM in your local schools.

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    U Bern [Universität Bern](CH) is a university in the Swiss capital of Bern and was founded in 1834. It is regulated and financed by the Canton of Bern. It is a comprehensive university offering a broad choice of courses and programs in eight faculties and some 150 institutes. With around 17,512 students, Universität Bern is the third biggest University in Switzerland.

    Universität Bern operates at three levels: university, faculties and institutes. Other organizational units include interfaculty and general university units. The university’s highest governing body is the Senate, which is responsible for issuing statutes, rules and regulations. Directly answerable to the Senate is the University Board of Directors, the governing body for university management and coordination. The Board comprises the Rector, the Vice-Rectors and the Administrative Director. The structures and functions of the University Board of Directors and the other organizational units are regulated by the Universities Act. Universität Bern offers about 39 bachelor and 72 master programs, with enrollments of 7,747 and 4,523, respectively. The university also has 2,776 doctoral students. Around 1,561 bachelor, 1,489 master’s degree students and 570 PhD students graduate each year. For some time now, the university has had more female than male students; at the end of 2016, women accounted for 56% of students.

    u-basel-campus

    Purposes

    The University of Basel [Universität Basel] (CH) fosters the development of critically thinking and tolerant individuals who are capable of taking initiative and taking on responsibility. It is the aim of the University to enable these individuals to deepen their knowledge and field-specific academic training and further education.

    Through research and teaching, the University imparts the insights past down over the ages in addition to producing new knowledge. It is guided by the principle of meaningfulness and purpose rather than feasibility.

    The University is aware of the duties arising from knowledge, fulfilling these duties through critical reflection and the services it provides. It takes its own position concerning problems facing society.

    The University realizes its aims by taking responsibility with respect to future generations, the society that supports them, the international academic community and the culture that is passed down from generation to generation.

     
  • richardmitnick 2:09 pm on January 21, 2021 Permalink | Reply
    Tags: "Electrons caught in the act", A team of researchers from the Faculty of Pure and Applied Sciences at the University of Tsukuba filmed the ultrafast motion of electrons with sub-nanoscale spatial resolution., Near picosecond time resolution for the first time, , Scanning tunneling microscopy,   

    From University of Tsukuba (筑波大学; Tsukuba daigaku) (JP) via phys.org: “Electrons caught in the act” 

    From University of Tsukuba (筑波大学; Tsukuba daigaku) (JP)

    via


    phys.org

    January 21, 2021

    1
    Fig.1 (a) Schematic illustration of the measurement setup. C60 thin-film sample has a structure consisting of several layers. (b) Snapshots of electron dynamics obtained over the area shown in the bottom STM image. Each snapshot represents the distribution of free electrons at 1, 3, 14, and 29 ps after the IR pulse excitation. The bottom is the STM image of the measurement area, and the location indicated by the dotted line in the STM image shows the steps formed by the molecular layers. Red (blue) color represents the area with higher (lower) electron density. The electron density decreased on the upper side of the steps as the color changes from red to blue, while electrons stayed even at 29 ps after the IR excitation on the lower side as the color remains red. Credit: University of Tsukuba.

    A team of researchers from the Faculty of Pure and Applied Sciences at the University of Tsukuba filmed the ultrafast motion of electrons with sub-nanoscale spatial resolution. This work provides a powerful tool for studying the operation of semiconductor devices, which can lead to more efficient electronic devices.

    The ability to construct ever smaller and faster smartphones and computer chips depends on the ability of semiconductor manufacturers to understand how the electrons that carry information are affected by defects. However, these motions occur on the scale of trillionths of a second, and they can only be seen with a microscope that can image individual atoms. It may seem like an impossible task, but this is exactly what a team of scientists at the University of Tsukuba was able to accomplish.

    The experimental system consisted of Buckminsterfullerene carbon molecules—which bear an uncanny resemblance to stitched soccer balls—arranged in a multilayer structure on a gold substrate. First, a scanning tunneling microscope was set up to capture the movies. To observe the motion of electrons, an infrared electromagnetic pump pulse was applied to inject electrons into the sample. Then, after a set time delay, a single ultrafast terahertz pulse was used to probe the location of the elections. Increasing the time delay allowed the next “frame” of the movie to be captured. This novel combination of scanning tunneling microscopy and ultrafast pulses allowed the team to achieve sub-nanoscale spatial resolution and near picosecond time resolution for the first time. “Using our method, we were able to clearly see the effects of imperfections, such as a molecular vacancy or orientational disorder,” explains first author Professor Shoji Yoshida. Capturing each frame took only about two minutes, which allows the results to be reproducible. This also makes the approach more practical as a tool for the semiconductor industry.

    “We expect that this technology will help lead the way towards the next generation of organic electronics,” senior author Professor Hidemi Shigekawa says. By understanding the effects of imperfections, some vacancies, impurities, or structural defects can be purposely introduced into devices to control their function.

    2
    Fig.2 Electron dynamics around a misoriented molecular defect. (a) STM image and snapshots obtained over an area including the defect indicated by the white arrow. Snapshots clearly show that electrons were still trapped in the single bright defect even 63 ps after IR pulse excitation as shown in (b). The defect appears brighter than the other C60 molecules because of the trap of electrons at the single molecular site. Credit: University of Tsukuba.

    Science paper:
    Terahertz Scanning Tunneling Microscopy for Visualizing Ultrafast Electron Motion in Nanoscale Potential Variations
    ACS Photonics

    See the full article here.

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Tsukuba (筑波大学; Tsukuba daigaku) (JP), located in Tsukuba, Ibaraki, is one of the prestigious national universities (established by Japanese Government). The university has 28 college clusters and schools with around 16,500 students (as of 2014). The main Tsukuba campus covers an area of 258 hectares (636 acres), making it the second largest single campus in Japan. The branch campus is in Bunkyo-ku, Tokyo, which offers graduate programs for working adults in the capital and manages K-12 schools in Tokyo that are attached to the university.

    The university’s academic strength is in STEMM fields (Science, Technology, Engineering, Mathematics, Medicine), physical education, and related interdisciplinary fields. It is by taking located in Tsukuba Science City which has more than 300 research institutions. The university has had three Nobel laureates (two in Physics and one in Chemistry, see also “History”), and about 70 athletes, their students and alumni, have participated in the Olympic Games.

    It has established interdisciplinary Ph.D. programs in Human Biology and Empowerment Informatics, and the International Institute for Integrative Sleep Medicine, which were created through the Ministry of Education, Culture, Sports, Science and Technology’s competitive funding projects.

    Its Graduate School of Life and Environmental Sciences is represented on the national Coordinating Committee for Earthquake Prediction.

     
  • richardmitnick 3:19 pm on November 23, 2020 Permalink | Reply
    Tags: "Direct visualization of quantum dots reveals shape of quantum wave function", Scanning tunneling microscopy, Trapping and controlling electrons in bilayer graphene quantum dots yields a promising platform for quantum information technologies.,   

    From UC Santa Cruz: “Direct visualization of quantum dots reveals shape of quantum wave function” 

    From UC Santa Cruz

    November 23, 2020
    Tim Stephens
    stephens@ucsc.edu

    Researchers used a scanning tunneling microscope to visualize quantum dots in bilayer graphene, an important step toward quantum information technologies.

    1
    Visualization of quantum dots in bilayer graphene using scanning tunneling microscopy and spectroscopy reveals a three-fold symmetry. In this three-dimensional image, the peaks represent sites of high amplitude in the waveform of the trapped electrons. Credit: Zhehao Ge, Frederic Joucken, and Jairo Velasco Jr.

    2
    The first direct visualization of quantum dots in bilayer graphene shows the shape of the quantum wave function of the trapped electrons. Credit: Zhehao Ge, Frederic Joucken, and Jairo Velasco Jr.

    Trapping and controlling electrons in bilayer graphene quantum dots yields a promising platform for quantum information technologies. Researchers at UC Santa Cruz have now achieved the first direct visualization of quantum dots in bilayer graphene, revealing the shape of the quantum wave function of the trapped electrons.

    The results, published November 23 in Nano Letters, provide important fundamental knowledge needed to develop quantum information technologies based on bilayer graphene quantum dots.

    “There has been a lot of work to develop this system for quantum information science, but we’ve been missing an understanding of what the electrons look like in these quantum dots,” said corresponding author Jairo Velasco Jr., assistant professor of physics at UC Santa Cruz.

    While conventional digital technologies encode information in bits represented as either 0 or 1, a quantum bit, or qubit, can represent both states at the same time due to quantum superposition. In theory, technologies based on qubits will enable a massive increase in computing speed and capacity for certain types of calculations.

    A variety of systems, based on materials ranging from diamond to gallium arsenide, are being explored as platforms for creating and manipulating qubits. Bilayer graphene (two layers of graphene, which is a two-dimensional arrangement of carbon atoms in a honeycomb lattice) is an attractive material because it is easy to produce and work with, and quantum dots in bilayer graphene have desirable properties.

    “These quantum dots are an emergent and promising platform for quantum information technology because of their suppressed spin decoherence, controllable quantum degrees of freedom, and tunability with external control voltages,” Velasco said.

    Understanding the nature of the quantum dot wave function in bilayer graphene is important because this basic property determines several relevant features for quantum information processing, such as the electron energy spectrum, the interactions between electrons, and the coupling of electrons to their environment.

    Velasco’s team used a method he had developed previously to create quantum dots in monolayer graphene using a scanning tunneling microscope (STM). With the graphene resting on an insulating hexagonal boron nitride crystal, a large voltage applied with the STM tip creates charges in the boron nitride that serve to electrostatically confine electrons in the bilayer graphene.

    “The electric field creates a corral, like an invisible electric fence, that traps the electrons in the quantum dot,” Velasco explained.

    The researchers then used the scanning tunneling microscope to image the electronic states inside and outside of the corral. In contrast to theoretical predictions, the resulting images showed a broken rotational symmetry, with three peaks instead of the expected concentric rings.

    “We see circularly symmetric rings in monolayer graphene, but in bilayer graphene the quantum dot states have a three-fold symmetry,” Velasco said. “The peaks represent sites of high amplitude in the wave function. Electrons have a dual wave-particle nature, and we are visualizing the wave properties of the electron in the quantum dot.”

    This work provides crucial information, such as the energy spectrum of the electrons, needed to develop quantum devices based on this system. “It is advancing the fundamental understanding of the system and its potential for quantum information technologies,” Velasco said. “It’s a missing piece of the puzzle, and taken together with the work of others, I think we’re moving toward making this a useful system.”

    In addition to Velasco, the authors of the paper include co-first authors Zhehao Ge, Frederic Joucken, and Eberth Quezada-Lopez at UC Santa Cruz, along with coauthors at the Federal University of Ceara, Brazil, the National Institute for Materials Science in Japan, University of Minnesota, and UCSC’s Baskin School of Engineering. This work was funded by the National Science Foundation and the Army Research Office.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC Lick Observatory, Mt Hamilton, in San Jose, California, Altitude 1,283 m (4,209 ft).

    UC Observatories Lick Automated Planet Finder, fully robotic 2.4-meter optical telescope at Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA.

    The UCO Lick C. Donald Shane telescope is a 120-inch (3.0-meter) reflecting telescope located at the Lick Observatory, Mt Hamilton, in San Jose, California, Altitude 1,283 m (4,209 ft).

    UC Santa Cruz campus.

    UCSC is the home base for the Lick Observatory.

    Lick Observatory’s 36-inch Great Great Refractor telescope housed in the South (large) Dome of main building.

     
  • richardmitnick 8:57 am on September 25, 2020 Permalink | Reply
    Tags: "Metal wires of carbon complete toolbox for carbon-based computers", , GNR's- graphene nanoribbons, Graphene- which is pure carbon is a leading contender for these next-generation carbon-based computers., Nanoribbons were created chemically and imaged on very flat surfaces using a scanning tunneling microscope., Scanning tunneling microscopy, The new nanoribbon’s electronic state was a metal with each segment contributing a single conducting electron., The set of tools needed to build working carbon circuits has remained incomplete until now., Transistors based on carbon rather than silicon could potentially boost computers’ speed and cut their power consumption more than a thousandfold., , Using chemistry we created a tiny change- a change in just one chemical bond per about every 100 atoms but which increased the metallicity of the nanoribbon by a factor of 20.   

    From UC Berkeley and Lawrence Berkeley National Laboratory: “Metal wires of carbon complete toolbox for carbon-based computers” 

    From UC Berkeley

    and


    Lawrence Berkeley National Laboratory

    September 24, 2020
    Robert Sanders
    rlsanders@berkeley.edu

    1
    Scanning tunneling microscope image of wide-band metallic graphene nanoribbon (GNR). Each cluster of protrusions corresponds to a singly-occupied electron orbital. The formation of a pentagonal ring near each cluster leads to a more than tenfold increase in the conductivity of metallic GNRs. The GNR backbone has a width of 1.6 nanometers. (UC Berkeley image by Daniel Rizzo)

    Transistors based on carbon rather than silicon could potentially boost computers’ speed and cut their power consumption more than a thousandfold — think of a mobile phone that holds its charge for months — but the set of tools needed to build working carbon circuits has remained incomplete until now.

    A team of chemists and physicists at the University of California, Berkeley, has finally created the last tool in the toolbox, a metallic wire made entirely of carbon, setting the stage for a ramp-up in research to build carbon-based transistors and, ultimately, computers.

    “Staying within the same material, within the realm of carbon-based materials, is what brings this technology together now,” said Felix Fischer, UC Berkeley professor of chemistry, noting that the ability to make all circuit elements from the same material makes fabrication easier. “That has been one of the key things that has been missing in the big picture of an all-carbon-based integrated circuit architecture.”

    Metal wires — like the metallic channels used to connect transistors in a computer chip — carry electricity from device to device and interconnect the semiconducting elements within transistors, the building blocks of computers.

    The UC Berkeley group has been working for several years on how to make semiconductors and insulators from graphene nanoribbons, which are narrow, one-dimensional strips of atom-thick graphene, a structure composed entirely of carbon atoms arranged in an interconnected hexagonal pattern resembling chicken wire.

    The new carbon-based metal is also a graphene nanoribbon, but designed with an eye toward conducting electrons between semiconducting nanoribbons in all-carbon transistors. The metallic nanoribbons were built by assembling them from smaller identical building blocks: a bottom-up approach, said Fischer’s colleague, Michael Crommie, a UC Berkeley professor of physics. Each building block contributes an electron that can flow freely along the nanoribbon.

    While other carbon-based materials — like extended 2D sheets of graphene and carbon nanotubes — can be metallic, they have their problems. Reshaping a 2D sheet of graphene into nanometer scale strips, for example, spontaneously turns them into semiconductors, or even insulators. Carbon nanotubes, which are excellent conductors, cannot be prepared with the same precision and reproducibility in large quantities as nanoribbons.

    “Nanoribbons allow us to chemically access a wide range of structures using bottom-up fabrication, something not yet possible with nanotubes,” Crommie said. “This has allowed us to basically stitch electrons together to create a metallic nanoribbon, something not done before. This is one of the grand challenges in the area of graphene nanoribbon technology and why we are so excited about it.”

    Metallic graphene nanoribbons — which feature a wide, partially-filled electronic band characteristic of metals — should be comparable in conductance to 2D graphene itself.

    “We think that the metallic wires are really a breakthrough; it is the first time that we can intentionally create an ultra-narrow metallic conductor — a good, intrinsic conductor — out of carbon-based materials, without the need for external doping,” Fischer added.

    Crommie, Fischer and their colleagues at UC Berkeley and Lawrence Berkeley National Laboratory (Berkeley Lab) will publish their findings in the Sept. 25 issue of the journal Science.

    Tweaking the topology

    Silicon-based integrated circuits have powered computers for decades with ever increasing speed and performance, per Moore’s Law, but they are reaching their speed limit — that is, how fast they can switch between zeros and ones. It’s also becoming harder to reduce power consumption; computers already use a substantial fraction of the world’s energy production. Carbon-based computers could potentially switch many times times faster than silicon computers and use only fractions of the power, Fischer said.

    Graphene, which is pure carbon, is a leading contender for these next-generation, carbon-based computers. Narrow strips of graphene are primarily semiconductors, however, and the challenge has been to make them also work as insulators and metals — opposite extremes, totally nonconducting and fully conducting, respectively — so as to construct transistors and processors entirely from carbon.

    Several years ago, Fischer and Crommie teamed up with theoretical materials scientist Steven Louie, a UC Berkeley professor of physics, to discover new ways of connecting small lengths of nanoribbon to reliably create the full gamut of conducting properties.

    Two years ago, the team demonstrated that by connecting short segments of nanoribbon in the right way, electrons in each segment could be arranged to create a new topological state — a special quantum wave function — leading to tunable semiconducting properties.

    In the new work, they use a similar technique to stitch together short segments of nanoribbons to create a conducting metal wire tens of nanometers long and barely a nanometer wide.

    The nanoribbons were created chemically and imaged on very flat surfaces using a scanning tunneling microscope. Simple heat was used to induce the molecules to chemically react and join together in just the right way. Fischer compares the assembly of daisy-chained building blocks to a set of Legos, but Legos designed to fit at the atomic scale.

    “They are all precisely engineered so that there is only one way they can fit together. It’s as if you take a bag of Legos, and you shake it, and out comes a fully assembled car,” he said. “That is the magic of controlling the self-assembly with chemistry.”

    Once assembled, the new nanoribbon’s electronic state was a metal — just as Louie predicted — with each segment contributing a single conducting electron.

    The final breakthrough can be attributed to a minute change in the nanoribbon structure.

    “Using chemistry, we created a tiny change, a change in just one chemical bond per about every 100 atoms, but which increased the metallicity of the nanoribbon by a factor of 20, and that is important, from a practical point of view, to make this a good metal,” Crommie said.

    The two researchers are working with electrical engineers at UC Berkeley to assemble their toolbox of semiconducting, insulating and metallic graphene nanoribbons into working transistors.

    “I believe this technology will revolutionize how we build integrated circuits in the future,” Fischer said. “It should take us a big step up from the best performance that can be expected from silicon right now. We now have a path to access faster switching speeds at much lower power consumption. That is what is driving the push toward a carbon-based electronics semiconductor industry in the future.”

    Co-lead authors of the paper are Daniel Rizzo and Jingwei Jiang from UC Berkeley’s Department of Physics and Gregory Veber from the Department of Chemistry. Other co-authors are Steven Louie, Ryan McCurdy, Ting Cao, Christopher Bronner and Ting Chen of UC Berkeley. Jiang, Cao, Louie, Fischer and Crommie are affiliated with Berkeley Lab, while Fischer and Crommie are members of the Kavli Energy NanoSciences Institute.

    The research was supported by the Office of Naval Research, the Department of Energy, the Center for Energy Efficient Electronics Science and the National Science Foundation.

    See the full article here .

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    LBNL Molecular Foundry

    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

    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

    UC Berkeley Seal

     
  • richardmitnick 12:00 pm on July 25, 2020 Permalink | Reply
    Tags: "Princeton scientists discover a topological magnet that exhibits exotic quantum effects", , Kagome lattice magnet, , , Princeton University - Discovery Magazine, Scanning tunneling microscopy   

    From Princeton University – Discovery Magazine: “Princeton scientists discover a topological magnet that exhibits exotic quantum effects” 

    Princeton University
    From Princeton University – Discovery Magazine

    1

    July 22, 2020
    Hasan group, Princeton University Department of Physics

    An international team led by researchers at Princeton University has uncovered a new class of magnet that exhibits novel quantum effects that extend to room temperature.

    The researchers discovered a quantized topological phase in a pristine magnet. Their findings provide insights into a 30-year-old theory of how electrons spontaneously quantize and demonstrate a proof-of-principle method to discover new topological magnets. Quantum magnets are promising platforms for dissipationless current, high storage capacity and future green technologies. The study was published in the journal Nature this week.

    The arrows represent the electron spins pointing up from a kagome lattice. The chirality is represented by the counterclockwise circle of fire, which represents the propagating electrons/current on the edge of the magnet. The two cones demonstrate that the bulk of the magnet contains Dirac fermions (linear or conical dispersion of bands) with an energy gap (Chern gap), making it topological.

    The discovery’s roots lie in the workings of the quantum Hall effect– a form of topological effect which was the subject of the Nobel Prize in Physics in 1985. This was the first time that a branch of theoretical mathematics, called topology, would start to fundamentally change how we describe and classify matter that makes up the world around us. Ever since, topological phases have been intensely studied in science and engineering. Many new classes of quantum materials with topological electronic structures have been found, including topological insulators and Weyl semimetals. However, while some of the most exciting theoretical ideas require magnetism, most materials explored have been nonmagnetic and show no quantization, leaving many tantalizing possibilities unfulfilled.

    “The discovery of a magnetic topological material with quantized behavior is a major step forward that could unlock new horizons in harnessing quantum topology for future fundamental physics and next-generation device research” said M. Zahid Hasan, the Eugene Higgins Professor of Physics at Princeton University, who led the research team.

    While experimental discoveries were rapidly being made, theoretical physics excelled at developing ideas leading to new measurements. Important theoretical concepts on 2D topological insulators were put forward in 1988 by F. Duncan Haldane, the Thomas D. Jones Professor of Mathematical Physics and the Sherman Fairchild University Professor of Physics at Princeton, who in 2016 was awarded the Nobel Prize in Physics for theoretical discoveries of topological phase transitions and topological phases of matter. Subsequent theoretical developments showed that topological insulator-hosting magnetism in a special atomic arrangement known as a kagome lattice can host some of the most bizarre quantum effects.

    Hasan and his team has been on a decade-long search for a topological magnetic quantum state that may also operate at room temperature since their discovery of the first examples of three dimensional topological insulators. Recently, they found a materials solution to Haldane’s conjecture in a kagome lattice magnet that is capable of operating at room temperature, which also exhibits the much desired quantization. “The kagome lattice can be designed to possess relativistic band crossings and strong electron-electron interactions. Both are essential for novel magnetism. Therefore, we realized that kagome magnets are a promising system in which to search for topological magnet phases as they are like the topological insulators that we studied before,” said Hasan.

    For so long, direct material and experimental visualization of this phenomenon has remained elusive. The team found that most of the kagome magnets were too difficult to synthesize, the magnetism was not sufficiently well understood, no decisive experimental signatures of the topology or quantization could be observed, or they operate only at very low temperatures.

    “A suitable atomic chemistry and magnetic structure design coupled to first-principles theory is the crucial step to make Duncan Haldane’s speculative prediction realistic in a high-temperature setting,” said Hasan. “There are hundreds of kagome magnets, and we need both intuition, experience, materials-specific calculations, and intense experimental efforts to eventually find the right material for in-depth exploration. And that took us on a decade-long journey.”

    Through several years of intense research on several families of topological magnets (Nature; Nature Physics; Physical Review Letters; Nature Communications; and Physical Review Letters ), the team gradually realized that a material made of the elements terbium, magnesium and tin (TbMn6Sn6) has the ideal crystal structure with chemically pristine, quantum mechanical properties and spatially segregated kagome lattice layers. Moreover, it uniquely features a strong out-of-plane magnetization. With this ideal kagome magnet successfully synthesized at the large single crystal level by collaborators from Shuang Jia’s group at Peking University, Hasan’s group began systematic state-of-the-art measurements to check whether the crystals are topological and, more important, feature the desired exotic quantum magnetic state.

    The Princeton team of researchers used an advanced technique known as scanning tunneling microscopy, which is capable of probing the electronic and spin wavefunctions of a material at the sub-atomic scale with sub-millivolt energy resolution. Under these fine-tuned conditions, the researchers identified the magnetic kagome lattice atoms in the crystal, findings that were further confirmed by state-of-the-art angle-resolved photoemission spectroscopy with momentum resolution.

    “The first surprise was that the magnetic kagome lattice in this material is super clean in our scanning tunneling microscopy,” said Songtian Sonia Zhang, a co-author of the study who earned her Ph.D. at Princeton earlier this year. “The experimental visualization of such a defect-free magnetic kagome lattice offers an unprecedented opportunity to explore its intrinsic topological quantum properties.”

    The real magical moment was when the researchers turned on a magnetic field. They found that the electronic states of the kagome lattice modulate dramatically, forming quantized energy levels in a way that is consistent with Dirac topology. By gradually raising the magnetic field to 9 Tesla, which is hundreds of thousands of times higher than the earth’s magnetic field, they systematically mapped out the complete quantization of this magnet. “It is extremely rare — there has not been one found yet — to find a topological magnetic system featuring the quantized diagram. It requires a nearly defect-free magnetic material design, fine-tuned theory and cutting-edge spectroscopic measurements” said Nana Shumiya, a graduate student and co-author of the study.

    The quantized diagram that the team measured provides precise information revealing that the electronic phase matches a variant of the Haldane model. It confirms that the crystal features a spin-polarized Dirac dispersion with a large Chern gap, as expected by the theory for topological magnets. However, one piece of the puzzle was still missing. “If this is truly a Chern gap, then based on the fundamental topological bulk-boundary principle, we should observe chiral (one-way traffic) states at the edge of the crystal,” Hasan said.

    The final piece fell into place when the researchers scanned the boundary or the edge of the magnet. They found a clear signature of an edge state only within the Chern energy gap. Propagating along the side of the crystal without apparent scattering (which reveals its dissipationless character), the state was confirmed to be the chiral topological edge state. Imaging of this state was unprecedented in any previous study of topological magnets.

    The researchers further used other tools to check and reconfirm their findings of the Chern gapped Dirac fermions, including electrical transport measurements of anomalous Hall scaling, angle-resolved photoemission spectroscopy of the Dirac dispersion in momentum space, and first-principles calculations of the topological order in the material family. The data provided a complete spectrum of inter-linked evidence all pointing to the realization of a quantum-limit Chern phase in this kagome magnet. “All the pieces fit together into a textbook demonstration of the physics of Chern-gapped magnetic Dirac fermions,” said Tyler A. Cochran, a graduate student and co-first author of the study.

    The researchers further used other tools to check and reconfirm their findings of the Chern gapped Dirac fermions, including electrical transport measurements of anomalous Hall scaling, angle-resolved photoemission spectroscopy of the Dirac dispersion in momentum space, and first-principles calculations of the topological order in the material family. The data provided a complete spectrum of inter-linked evidence all pointing to the realization of a quantum-limit Chern phase in this kagome magnet. “All the pieces fit together into a textbook demonstration of the physics of Chern-gapped magnetic Dirac fermions,” said Tyler A. Cochran, a graduate student and co-first author of the study.

    Now the theoretical and experimental focus of the group is shifting to the dozens of compounds with similar structures to TbMn6Sn6 that host kagome lattices with a variety of magnetic structures, each with its individual quantum topology. “Our experimental visualization of the quantum limit Chern phase demonstrates a proof-of-principle methodology to discover new topological magnets,” said Jia-Xin Yin, a senior postdoctoral researcher and another co-first author of the study.

    “This is like discovering water in an exoplanet – it opens up a new frontier of topological quantum matter research our laboratory at Princeton has been optimized for,” Hasan said.

    The study, “Quantum-limit Chern magnetism in TbMn6Sn6,” by Jia-Xin Yin, Wenlong Ma, Tyler A. Cochran, Xitong Xu, Songtian S. Zhang, Hung-Ju Tien, Nana Shumiya, Guangming Cheng, Kun Jiang, Biao Lian, Zhida Song, Guoqing Chang, Ilya Belopolski, Daniel Multer, Maksim Litskevich, Zi-Jia Cheng, Xian P. Yang, Bianca Swidler, Huibin Zhou, Hsin Lin, Titus Neupert, Ziqiang Wang, Nan Yao, Tay-Rong Chang, Shuang Jia and M. Zahid Hasan, was published in the journal Nature on July 22, 2020, volume 583, pages 533–536(2020). DOI: 10.1038/s41586-020-2482-7.

    The STM experimental work and the theoretical prediction of topological materials were supported by the Gordon and Betty Moore Foundation under grant GBMF9461/HASAN. The ARPES part of the experiment was supported by the U.S. Department of Energy Basic Energy Sciences under grant DOE/BES DE-FG-02-05ER46200 and DE-FG02-99ER45747. Work at Princeton’s Imaging and Analysis Center is supported by the Princeton Center for Complex Materials, a National Science Foundation (NSF)-MRSEC program, under grant DMR-1420541. Additional support comes from the National Science Foundation Graduate Research Fellowship Program under grant number DGE-1656466. This research used resources of the Advanced Light Source, a DOE Office of Science User Facility under grant DE-AC02-05CH11231.

    LBNL ALS

    See the full article here .

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    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

    Princeton Shield

     
  • richardmitnick 12:41 pm on April 3, 2020 Permalink | Reply
    Tags: , , , , Scanning tunneling microscopy, , UTe2-Uranium ditelluride-an unconventional superconductor   

    From University of Illinois via phys.org: “New measurements reveal evidence of elusive particles in a newly-discovered superconductor” 

    U Illinois bloc

    From University of Illinois

    via


    phys.org

    April 3, 2020
    Emily Edwards

    1
    New measurements show evidence for the presence of exotic Majorana particles on the surface of an unconventional superconductor, Uranium ditelluride. Credit: Dr. E. Edwards, Managing Director of Illinois Quantum Information Science and Technology Center (IQUIST).

    Particle chasing—it’s a game that so many physicists play. Sometimes the hunt takes place inside large supercolliders, where spectacular collisions are necessary to find hidden particles and new physics. For physicists studying solids, the game occurs in a much different environment and the sought-after particles don’t come from furious collisions. Instead, particle-like entities, called quasiparticles, emerge from complicated electronic interactions that happen deep within a material. Sometimes the quasiparticles are easy to probe, but others are more difficult to spot, lurking just out of reach.

    New measurements show evidence for the presence of exotic Majorana particles on the surface of an unconventional superconductor, Uranium ditelluride. Graphic provided by Dr. E. Edwards, Managing Director of Illinois Quantum Information Science and Technology Center (IQUIST).

    Now a team of researchers at the University of Illinois, led by physicist Vidya Madhavan, in collaboration with researchers from the National Institute of Standards and Technology, the University of Maryland, Boston College, and ETH Zürich, have used high-resolution microscopy tools to peer at the inner-workings of an unusual type of superconductor, uranium ditelluride (UTe2). Their measurements reveal strong evidence that this material may be a natural home to an exotic quasiparticle that’s been hiding from physicists for decades. The study is published in the March 26 issue of Nature.

    The particles in question were theorized back in 1937 by an Italian physicist named Ettore Majorana, and since then, physicists have been trying to prove that they can exist. Scientists think a particular class of materials called chiral unconventional superconductors may naturally host Majoranas. UTe2 may have all of the right properties to spawn these elusive quasiparticles.

    “We know the physics of conventional superconductors and understand how they can conduct electricity or transport electrons from one end of a wire to the other with no resistance,” said Madhavan. “Chiral unconventional superconductors are much rarer, and the physics is less well known. Understanding them is important for fundamental physics and has potential applications in quantum computing,” she said.

    Inside of a normal superconductor, the electrons pair up in a way that enables the lossless, persistent currents. This is in contrast to a normal conductor, like copper wire, which heats up as current passes through it. Part of the theory behind superconductivity was formulated decades ago by three scientists at the U of I who earned a Nobel prize in physics for their work. For this conventional kind of superconductivity, magnetic fields are the enemy and break up the pairs, returning the material back to normal. Over the last year, researchers showed that uranium ditelluride behaves differently.

    In 2019, Sheng Ran, Nicholas Butch (both co-authors on this study) and their collaborators announced that UTe2 remains superconducting in the presence of magnetic fields up to 65 Tesla, which is about 10,000 times stronger than a refrigerator magnet. This unconventional behavior, combined with other measurements, led the authors of that paper to surmise that the electrons were pairing up in an unusual way that enabled them to resist break-ups. The pairing is important because superconductors with this property could very likely have Majorana particles on the surface. The new study from Madhavan and collaborators strengthens the case for this.

    The team used a high-resolution microscope called a scanning tunneling microscope to look for evidence of the unusual electron pairing and Majorana particles. This microscope can not only map out the surface of uranium ditelluride down to the level of atoms but also probe what’s happening with the electrons. The material itself is silvery with steps jutting up from the surface. These step features are where evidence for Majorana quasiparticles is best seen. They provide a clean edge that, if predictions are correct, should show signatures of a continuous current that moves in one direction, even without the application of a voltage. The team scanned opposite sides of the step and saw a signal with a peak. But the peak was different, depending on which side of the step was scanned.

    “Looking at both sides of the step, you see a signal that is a mirror image of each other. In a normal superconductor, you cannot find that,” said Madhavan. “The best explanation for seeing the mirror images is that we are directly measuring the presence of moving Majorana particles,” said Madhavan. The team says that the measurements indicate that free-moving Majorana quasiparticles are circulating together in one direction, giving rise to mirrored, or chiral, signals.

    Madhavan says the next step is to make measurements that would confirm that the material has broken time-reversal symmetry. This means that the particles should move differently if the arrow of time were theoretically reversed. Such a study would provide additional evidence for the chiral nature of UTe2.

    If confirmed, uranium ditelluride would be the only material, other than superfluid He-3, proven to be a chiral unconventional superconductor. “This is a huge discovery that will allow us to understand this rare kind of superconductivity, and maybe, in time, we could even manipulate Majorana quasiparticles in a useful way for quantum information science.”

    See the full article here .

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    U Illinois campus

    The University of Illinois at Urbana-Champaign community of students, scholars, and alumni is changing the world.

    With our land-grant heritage as a foundation, we pioneer innovative research that tackles global problems and expands the human experience. Our transformative learning experiences, in and out of the classroom, are designed to produce alumni who desire to make a significant, societal impact.

    The University of Illinois at Chicago (UIC) is a public research university in Chicago, Illinois. Its campus is in the Near West Side community area, adjacent to the Chicago Loop. The second campus established under the University of Illinois system, UIC is also the largest university in the Chicago area, having approximately 30,000 students[9] enrolled in 15 colleges.

    UIC operates the largest medical school in the United States with research expenditures exceeding $412 million and consistently ranks in the top 50 U.S. institutions for research expenditures.[10][11][12] In the 2019 U.S. News & World Report’s ranking of colleges and universities, UIC ranked as the 129th best in the “national universities” category.[13] The 2015 Times Higher Education World University Rankings ranked UIC as the 18th best in the world among universities less than 50 years old.[14]

    UIC competes in NCAA Division I Horizon League as the UIC Flames in sports. The Credit Union 1 Arena (formerly UIC Pavilion) is the Flames’ venue for home games.

     
  • richardmitnick 9:23 am on November 21, 2019 Permalink | Reply
    Tags: , , , , , Oxygen like sulfur and selenium is part of the oxygen or “chalcogen” family of elements., Scanning tunneling microscopy,   

    From Lawrence Berkeley National Lab: “The Beauty of Imperfections: Linking Atomic Defects to 2D Materials’ Electronic Properties” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    November 20, 2019
    Theresa Duque
    tnduque@lbl.gov
    (510) 495-2418

    Scientists at Berkeley Lab reveal oxygen’s hidden talent for filling in atomic gaps in TMDs; and the surprising role of electron spin in conductivity.

    1
    Scanning tunneling microscopy image of an oxygen substituting sulfur (left), and a sulfur vacancy (right) in tungsten disulfide. In comparison, a strand of human DNA is 2.5 nanometers (nm) in diameter, and a strand of human hair is about 100,000 nm wide. (Credit: Berkeley Lab)

    Like any material, atomically thin, 2D semiconductors known as TMDs or transition metal dichalcogenides are not perfect, but their imperfections can actually be a good thing.

    Understanding how defects are structured at the atomic scale, how they are created, and how they interact with electrons are the first steps to designing new advanced materials. However, no one has been able to link useful properties like optical absorption and emission, conductivity, or catalytic function to specific defects in TMDs.

    Now, two studies led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have revealed surprising details on how some atomic defects emerge in TMDs, and how those defects shape the 2D material’s electronic properties. Their findings could provide a more versatile yet targeted platform for designing 2D materials for quantum information science and smaller, more powerful next-generation light-based electronics (optoelectronics).

    A quantum tip for 2D materials

    In the world of materials science, many researchers assumed that the most abundant defects in TMDs were the result of missing atoms or “vacancies” of sulfur in tungsten disulfide (WS2), or selenium vacancies in molybdenum diselenide (MoSe2).

    But as reported in Nature Communications, the researchers found that the defects previously observed with other methods were actually created by oxygen atoms replacing sulfur or selenium atoms, said D. Frank Ogletree, a staff scientist at Berkeley Lab’s Molecular Foundry and a co-author of the two studies.

    Oxygen, like sulfur and selenium, is part of the oxygen or “chalcogen” family of elements. And since chalcogens share similar properties, there isn’t much change in conductivity when an oxygen atom takes the place of a sulfur or selenium atom in a TMD crystal structure, he said.

    2
    Atomic force microscopy image of sulfur vacancy in tungsten disulfide. (Credit: Berkeley Lab)

    “In other words, it’s like exchanging one kind of apple for another,” explained co-lead author Bruno Schuler, a postdoctoral researcher at Berkeley Lab’s Molecular Foundry. “So when an oxygen atom fills in for a missing sulfur or selenium atom, it effectively restores the TMD’s electronic properties.”

    Co-lead author with Schuler is Sara Barja, who was a postdoctoral researcher in Berkeley Lab’s Materials Sciences Division at the time of the Nature Communications study.

    Key to their finding was the use of the Molecular Foundry’s atomic force microscope (AFM), with a single carbon monoxide (CO) molecule acting as an ultrasharp “tip” or probe, and scanning tunneling microscope (STM). They also benefited from state-of-the-art calculations carried out by scientists from Berkeley Lab’s Center for Computational Study of Excited State Phenomena in Energy Materials (C2SEPEM).

    When used with AFM, the CO-tip images the surface atoms at a very high resolution that’s not possible with conventional techniques, and precisely pinpoints the defect’s atomic site; STM provides the defect’s unique electronic fingerprint.

    The combined insights from both of these methods, combined with detailed calculations performed at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), ultimately helped us understand what these defects are and why they behave the way they do,” said author Alexander Weber-Bargioni, who led the studies. Weber-Bargioni is the facility director for Imaging and Manipulation of Nanostructures at Berkeley Lab’s Molecular Foundry.

    NERSC at LBNL

    NERSC Cray Cori II supercomputer, named after Gerty Cori, the first American woman to win a Nobel Prize in science

    NERSC Hopper Cray XE6 supercomputer, named after Grace Hopper, One of the first programmers of the Harvard Mark I computer

    NERSC Cray XC30 Edison supercomputer

    NERSC GPFS for Life Sciences


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF computer cluster in 2003.

    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    Future:

    Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supeercomputer

    NERSC is a DOE Office of Science User Facility.

    The unexpected power of an orbiting electron’s spin.

    In the researchers’ second study, published in Physical Review Letters, they demonstrated how to deliberately create chalcogen vacancies by heating a sample of WS2 in vacuum up to 600 degrees Celsius (1,112 degrees Fahrenheit), resulting in a thermal energy that causes the atoms to vibrate. “The vibrations kick out one of the sulfur atoms, creating an atomic hole in the material’s crystalline structure,” explained lead author Schuler.

    The scientists also discovered that “spin-orbit interaction” – which relates to the properties of electrons orbiting around an atom’s nucleus and in their own inherent directional spin – plays a significant role in the electronic structure of chalcogen vacancies.

    “In many cases the electron orbital and spin are autonomous and do not care about each other,” he said. “But in some cases, as we discovered in our study, they interact and form hybrid states of electronic structure.”

    Schuler noted that the impact of spin-orbit interaction on the electronic structure of defect sites in TMDs wasn’t clearly understood before this study.

    “It wasn’t even on anyone’s radar. We’re the first to prove it not only by quantitatively determining the magnitude of spin-orbit coupling but also by directly imaging the defect’s electronic orbitals,” he said.

    Now that the researchers have successfully demonstrated how to create chalcogen vacancies in TMDs, Schuler said that they plan to explore the engineering of atomic defects in other types of 2D materials, such as the creation of distinct spin-polarized states, which would be useful for realizing atomic quantum light emitters and other such devices.

    Co-corresponding author Jeff Neaton, a senior faculty scientist in Berkeley Lab’s Materials Sciences Division and professor of physics at UC Berkeley, said that Berkeley Lab offers a unique venue for carrying out multidisciplinary studies.

    “By combining novel experiments at the Molecular Foundry with leading-edge theory, and computing defects’ properties at NERSC with computational methods developed at C2SEPEM, we are steps closer to understanding how common defects can be used to tune optoelectronic properties in 2D materials,” he said.

    Participants in the Nature Communications study involved researchers from Berkeley Lab; UC Berkeley; the University of the Basque Country UPV/EHU-CSIC, Basque Foundation for Science, and Donostia International Physics Center, Spain; Ecole Polytechnique Fédérale de Lausanne, Switzerland; the Korea Institute of Science and Technology; Pusan National University, Korea; and the Weizmann Institute of Science, Israel.

    Participants in the Physical Review Letters study involved researchers from Berkeley Lab; UC Berkeley; Weizmann Institute of Science, Israel; Technical University of Munich; University of the Basque Country UPV/EHU-CSIC, Basque Foundation for Science, and Donostia International Physics Center, Spain.

    Postdoctoral researchers Christoph Kastl and Christopher Chen of the Molecular Foundry grew the tungsten disulfide samples for the Nature Communications and Physical Review Letters studies; and Hyejin Ryu, a doctoral researcher at the Advanced Light Source (ALS), grew samples of molybdenum diselenide for the Nature Communications study.

    LBNL ALS

    The work for both studies was supported by the U.S. Department of Energy’s Office of Science, including the Computational Materials Sciences Center for Computational Study of Excited State Phenomena in Energy Materials (C2SEPEM); research at the Molecular Foundry, a DOE Office of Science user facility that specializes in nanoscale science; and resources at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC). Resources at the Advanced Light Source (ALS) were used for the Nature Communications study.

    The U.S. National Science Foundation provided additional funding for the Nature Communications study, and the DOE Early Career Research Program provided additional funding for the Physical Review Letters study.

    NERSC and the ALS are also DOE Office of Science user facilities.

    See the full article here .

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    LBNL campus

    LBNL Molecular Foundry

    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

     
  • richardmitnick 8:59 am on July 30, 2019 Permalink | Reply
    Tags: A team of physicists at University of Illinois at Chicago and the University of Hamburg have taken a different approach., Entangled Majorana quasiparticles produced by splitting an electron into two halves are surprisingly stable., , , Majorana quasiparticles, , , , , Scanning tunneling microscopy, , They remember how they've been moved around a property that could be exploited for storing information., They've started with a rhenium superconductor a material that conducts electricity with zero resistance when supercooled to around 6 Kelvin (–267°C; 449°F)., , ,   

    From University of Illinois and U Hamburg, via Science Alert: “An Elusive Particle That Acts as Its Own Antiparticle Has Just Been Imaged” 

    U Illinois bloc

    From University of Illinois Chicago

    and

    2
    U Hamburg

    via

    30 JULY 2019
    MICHELLE STARR

    3
    (Palacio-Morales et al. Science Advances, 2019)

    New images of the Majorana fermion have brought physicists a step closer to harnessing the mysterious objects for quantum computing.

    These strange objects – particles that acts as their own antiparticles – have a vast as-yet untapped potential to act as qubits, the quantum bits that are the basic units of information in a quantum computer.

    IBM iconic image of Quantum computer

    They’re equivalent to binary bits in a traditional computer. But, where regular bits can represent a 1 or a 0, qubits can be either 1, 0 or both at the same time, a state known as quantum superposition. Quantum superposition is actually pretty hard to maintain, although we’re getting better at it.

    This is where Majorana quasiparticles come in. These are excitations in the collective behaviour of electrons that act like Majorana fermions, and they have a number of properties that make them an attractive candidate for qubits.

    Normally, a particle and an antiparticle will annihilate each other, but entangled Majorana quasiparticles produced by splitting an electron into two halves are surprisingly stable. In addition, they remember how they’ve been moved around, a property that could be exploited for storing information.

    But the quasiparticles have to remain separated by a sufficient distance. This can be done with a special nanowire, but a team of physicists at the University of Illinois at Chicago and the University of Hamburg in Germany have taken a different approach.

    They’ve started with a rhenium superconductor, a material that conducts electricity with zero resistance when supercooled to around 6 Kelvin (–267°C; 449°F).

    On top of these superconductors, the researchers deposited nanoscale islands of single layers of magnetic iron atoms. This creates what is known as a topological superconductor – that is, a superconductor that contains a topological knot.

    “This topological knot is similar to the hole in a donut,” explained physicist Dirk Morr of the University of Illinois at Chicago.

    “You can deform the donut into a coffee mug without losing the hole, but if you want to destroy the hole, you have to do something pretty dramatic, such as eating the donut.”

    When electrons flow through the superconductor, the team predicted that Majorana fermions would appear in a one-dimensional mode at the edges of the iron islands – around the so-called donut hole. And that by using a scanning tunneling microscope – an instrument used for imaging surfaces at the atomic level – they would see this visualised as a bright line.

    Sure enough, a bright line showed up.

    It’s not the first time Majorana fermions have been imaged, but it does represent a step forward. And just last month, a different team of researchers revealed that they had been able to turn Majorana quasiparticles on and off.

    But being able to visualise these particles, the researchers said, brings us closer to using them as qubits.

    “The next step will be to figure out how we can quantum engineer these Majorana qubits on quantum chips and manipulate them to obtain an exponential increase in our computing power,” Morr said.

    The research has been published in Science Advances.

    See the full article here .

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    4

    The University

    Universität Hamburg is the largest institution for research and education in northern Germany. As one of the country’s largest universities, we offer a diverse range of degree programs and excellent research opportunities. The University boasts numerous interdisciplinary projects in a broad range of fields and an extensive partner network of leading regional, national, and international higher education and research institutions.
    Sustainable science and scholarship

    Universität Hamburg is committed to sustainability. All our faculties have taken great strides towards sustainability in both research and teaching.
    Excellent research

    As part of the Excellence Strategy of the Federal and State Governments, Universität Hamburg has been granted clusters of excellence for 4 core research areas: Advanced Imaging of Matter (photon and nanosciences), Climate, Climatic Change, and Society (CliCCS) (climate research), Understanding Written Artefacts (manuscript research) and Quantum Universe (mathematics, particle physics, astrophysics, and cosmology).

    An equally important core research area is Infection Research, in which researchers investigate the structure, dynamics, and mechanisms of infection processes to promote the development of new treatment methods and therapies.
    Outstanding variety: over 170 degree programs

    Universität Hamburg offers approximately 170 degree programs within its eight faculties:

    Faculty of Law
    Faculty of Business, Economics and Social Sciences
    Faculty of Medicine
    Faculty of Education
    Faculty of Mathematics, Informatics and Natural Sciences
    Faculty of Psychology and Human Movement Science
    Faculty of Business Administration (Hamburg Business School).

    Universität Hamburg is also home to several museums and collections, such as the Zoological Museum, the Herbarium Hamburgense, the Geological-Paleontological Museum, the Loki Schmidt Garden, and the Hamburg Observatory.
    History

    Universität Hamburg was founded in 1919 by local citizens. Important founding figures include Senator Werner von Melle and the merchant Edmund Siemers. Nobel Prize winners such as the physicists Otto Stern, Wolfgang Pauli, and Isidor Rabi taught and researched at the University. Many other distinguished scholars, such as Ernst Cassirer, Erwin Panofsky, Aby Warburg, William Stern, Agathe Lasch, Magdalene Schoch, Emil Artin, Ralf Dahrendorf, and Carl Friedrich von Weizsäcker, also worked here.
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    U Illinois campus

    The University of Illinois at Urbana-Champaign community of students, scholars, and alumni is changing the world.

    With our land-grant heritage as a foundation, we pioneer innovative research that tackles global problems and expands the human experience. Our transformative learning experiences, in and out of the classroom, are designed to produce alumni who desire to make a significant, societal impact.

    The University of Illinois at Chicago (UIC) is a public research university in Chicago, Illinois. Its campus is in the Near West Side community area, adjacent to the Chicago Loop. The second campus established under the University of Illinois system, UIC is also the largest university in the Chicago area, having approximately 30,000 students[9] enrolled in 15 colleges.

    UIC operates the largest medical school in the United States with research expenditures exceeding $412 million and consistently ranks in the top 50 U.S. institutions for research expenditures.[10][11][12] In the 2019 U.S. News & World Report’s ranking of colleges and universities, UIC ranked as the 129th best in the “national universities” category.[13] The 2015 Times Higher Education World University Rankings ranked UIC as the 18th best in the world among universities less than 50 years old.[14]

    UIC competes in NCAA Division I Horizon League as the UIC Flames in sports. The Credit Union 1 Arena (formerly UIC Pavilion) is the Flames’ venue for home games.

     
  • richardmitnick 9:37 pm on October 5, 2018 Permalink | Reply
    Tags: 'Choosy' Electronic Correlations Dominate Metallic State of Iron Superconductor, , , , , , , , Scanning tunneling microscopy   

    From Brookhaven National Lab: “‘Choosy’ Electronic Correlations Dominate Metallic State of Iron Superconductor” 

    From Brookhaven National Lab

    October 3, 2018
    Ariana Tantillo
    atantillo@bnl.gov

    Finding could lead to a universal explanation of how two radically different types of materials—an insulator and a metal—can perfectly carry electrical current at relatively high temperatures.

    1
    Scientists discovered strong electronic correlations in certain orbitals, or energy shells, in the metallic state of the high-temperature superconductor iron selenide (FeSe). A schematic of the arrangement of the Se and Fe atoms is shown on the left; on the right is an image of the Se atoms in the termination layer of an FeSe crystal. Only the electron orbitals from the Fe atoms contribute to the orbital selectivity in the metallic state.

    Two families of high-temperature superconductors (HTS)—materials that can conduct electricity without energy loss at unusually high (but still quite cold) temperatures—may be more closely related than scientists originally thought.

    Beyond their layered crystal structures and the fact that they become superconducting when “doped” with atoms of other elements and cooled to a critical temperature, copper-based and iron-based HTS seemingly have little in common. After all, one material is normally an insulator (copper-based), and the other is a metal (iron-based). But a multi-institutional team of scientists has now presented new evidence suggesting that these radically different materials secretly share an important feature: strong electronic correlations. Such correlations occur when electrons move together in a highly coordinated way.

    “Theory has long predicted that strong electronic correlations can remain hidden in plain sight in a Hund’s metal,” said team member J.C. Seamus Davis, a physicist in the Condensed Matter Physics and Materials Science at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and the James Gilbert White Distinguished Professor in the Physical Sciences at Cornell University. “A Hund’s metal is a unique new type of electronic fluid in which the electrons from different orbitals, or energy shells, maintain very different degrees of correlation as they move through the material. By visualizing the orbital identity and correlation strength for different electrons in the metal iron selenide (FeSe), we discovered that orbital-selective strong correlations are present in this iron-based HTS.”

    It is yet to be determined if such correlations are characteristic of iron-based HTS in general. If proven to exist across both families of materials, they would provide the universal key ingredient in the recipe for high-temperature superconductivity. Finding this recipe has been a holy grail of condensed matter physics for decades, as it is key to developing more energy-efficient materials for medicine, electronics, transportation, and other applications.

    Experiment meets theory

    Since the discovery of iron-based HTS in 2008 (more than 20 years after that of copper-based HTS), scientists have been trying to understand the behavior of these unique materials. Confusion arose immediately because high-temperature superconductivity in copper-based materials emerges from a strongly correlated insulating state, but in iron-based HTS, it always emerges from a metallic state that lacks direct signatures of correlations. This distinction suggested that strong correlations were not essential—or perhaps even relevant—to high-temperature superconductivity. However, advanced theory soon provided another explanation. Because Fe-based materials have multiple active Fe orbitals, intense electronic correlations could exist but remain hidden due to orbital selectivity in the Hund’s metal state, yet still generate high-temperature superconductivity.

    In this study, recently described in Nature Materials, the team—including Brian Andersen of Copenhagen University, Peter Hirschfeld of the University of Florida, and Paul Canfield of DOE’s Ames National Laboratory—used a scanning tunneling microscope to image the quasiparticle interference of electrons in FeSe samples synthesized and characterized at Ames National Lab. Quasiparticle interference refers to the wave patterns that result when electrons are scattered due to atomic-scale defects—such as impurity atoms or vacancies—in the crystal lattice.

    2
    The spectroscopic imaging scanning tunneling microscope used for this study, in three different views.

    Spectroscopic imaging scanning tunneling microcopy can be used to visualize these interference patterns, which are characteristic of the microscopic behavior of electrons. In this technique, a single-atom probe moves back and forth very close to the sample’s surface in extremely tiny steps (as small as two trillionths of a meter) while measuring the amount of electrical current that is flowing between the single atom on the probe tip and the material, under an applied voltage.

    Their analysis of the interference patterns in FeSe revealed that the electronic correlations are orbitally selective—they depend on which orbital each electron comes from. By measuring the strength of the electronic correlations (i.e., amplitude of the quasiparticle interference patterns), they determined that some orbitals show very weak correlation, whereas others show very strong correlation.

    The next question to investigate is whether the orbital-selective electronic correlations are related to superconductivity. If the correlations act as a “glue” that binds electrons together into the pairs required to carry superconducting current—as is thought to happen in the copper-oxide HTS—a single picture of high-temperature superconductivity may emerge.

    Experimental studies were carried out by the former Center for Emergent Superconductivity, a DOE Energy Frontier Research Center at Brookhaven, and the research was supported by DOE’s Office of Science, the Moore Foundation’s Emergent Phenomena in Quantum Physics (EPiQS) Initiative, and a Lundbeckfond Fellowship.

    See the full article here .


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  • richardmitnick 11:58 am on February 12, 2018 Permalink | Reply
    Tags: , Scanning tunneling microscopy,   

    From U Texas Dallas: “UT Dallas Team’s Microscopic Solution May Save Researchers Big Time” 

    U Texas Dallas

    Feb. 12, 2018

    A University of Texas at Dallas graduate student, his advisor and industry collaborators believe they have addressed a long-standing problem troubling scientists and engineers for more than 35 years: How to prevent the tip of a scanning tunneling microscope from crashing into the surface of a material during imaging or lithography.

    2
    IBM Scanning tunneling microscope

    Details of the group’s solution appeared in the January issue of the journal Review of Scientific Instruments, which is published by the American Institute of Physics.

    Scanning tunneling microscopes (STMs) operate in an ultra-high vacuum, bringing a fine-tipped probe with a single atom at its apex very close to the surface of a sample. When voltage is applied to the surface, electrons can jump or tunnel across the gap between the tip and sample.

    1
    Farid Tajaddodianfar

    “Think of it as a needle that is very sharp, atomically sharp,” said Farid Tajaddodianfar, a mechanical engineering graduate student in the Erik Jonsson School of Engineering and Computer Science. “The microscope is like a robotic arm, able to reach atoms on the sample surface and manipulate them.”

    The problem is, sometimes the tungsten tip crashes into the sample. If it physically touches the sample surface, it may inadvertently rearrange the atoms or create a “crater,” which could damage the sample. Such a “tip crash” often forces operators to replace the tip many times, forfeiting valuable time.

    Dr. John Randall is an adjunct professor at UT Dallas and president of Zyvex Labs, a Richardson, Texas-based nanotechnology company specializing in developing tools and products that fabricate structures atom by atom. Zyvex reached out to Dr. Reza Moheimani, a professor of mechanical engineering, to help address STMs’ tip crash problem. Moheimani’s endowed chair was a gift from Zyvex founder James Von Ehr MS’81, who was honored as a distinguished UTD alumnus in 2004.

    “What they’re trying to do is help bring atomically precise manufacturing into reality,” said Randall, who co-authored the article with Tajaddodianfar, Moheimani and Zyvex Labs’ James Owen. “This is considered the future of nanotechnology, and it is extremely important work.”

    Randall said such precise manufacturing will lead to a host of innovations.

    “By building structures atom by atom, you’re able to create new, extraordinary materials,” said Randall, who is co-chair of the Jonsson School’s Industry Engagement Committee. “We can remove impurities and make materials stronger and more heat resistant. We can build quantum computers. It could radically lower costs and expand capabilities in medicine and other areas. For example, if we can better understand DNA at an atomic and molecular level, that will help us fine-tune and tailor health care according to patients’ needs. The possibilities are endless.”

    In addition, Moheimani, a control engineer and expert in nanotechnology, said scientists are attempting to build transistors and quantum computers from a single atom using this technology.

    “There’s an international race to build machines, devices and 3-D equipment from the atom up,” said Moheimani, the James Von Ehr Distinguished Chair in Science and Technology.

    ‘It’s a Big, Big Problem’

    Randall said Zyvex Labs has spent a lot of time and money trying to understand what happens to the tips when they crash.

    “It’s a big, big problem,” Randall said. “If you can’t protect the tip, you’re not going to build anything. You’re wasting your time.”

    Tajaddodianfar and Moheimani said the issue is the controller.

    “There’s a feedback controller in the STM that measures the current and moves the needle up and down,” Moheimani said. “You’re moving from one atom to another, across an uneven surface. It is not flat. Because of that, the distance between the sample and tip changes, as does the current between them. While the controller tries to move the tip up and down to maintain the current, it does not always respond well, nor does it regulate the tip correctly. The resulting movement of the tip is often unstable.”

    It’s the feedback controller that fails to protect the tip from crashing into the surface, Tajaddodianfar said.

    “When the electronic properties are variable across the sample surface, the tip is more prone to crash under conventional control systems,” he said. “It’s meant to be really, really sharp. But when the tip crashes into the sample, it breaks, curls backward and flattens.

    “Once the tip crashes into the surface, forget it. Everything changes.”

    The Solution

    According to Randall, Tajaddodianfar took logical steps for creating the solution.

    “The brilliance of Tajaddodianfar is that he looked at the problem and understood the physics of the tunneling between the tip and the surface, that there is a small electronic barrier that controls the rate of tunneling,” Randall said. “He figured out a way of measuring that local barrier height and adjusting the gain on the control system that demonstrably keeps the tip out of trouble. Without it, the tip just bumps along, crashing into the surface. Now, it adjusts to the control parameters on the fly.”

    Moheimani said the group hopes to change their trajectory when it comes to building new devices.

    “That’s the next thing for us. We set out to find the source of this problem, and we did that. And, we’ve come up with a solution. It’s like everything else in science: Time will tell how impactful our work will be,” Moheimani said. “But I think we have solved the big problem.”

    Randall said Tajaddodianfar’s algorithm has been integrated with its system’s software but is not yet available to customers. The research was made possible by funding from the Army Research Office and the Defense Advanced Research Projects Agency.

    See the full article here .

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    The University of Texas at Dallas is a Carnegie R1 classification (Doctoral Universities – Highest research activity) institution, located in a suburban setting 20 miles north of downtown Dallas. The University enrolls more than 27,600 students — 18,380 undergraduate and 9,250 graduate —and offers a broad array of bachelor’s, master’s, and doctoral degree programs.

    Established by Eugene McDermott, J. Erik Jonsson and Cecil Green, the founders of Texas Instruments, UT Dallas is a young institution driven by the entrepreneurial spirit of its founders and their commitment to academic excellence. In 1969, the public research institution joined The University of Texas System and became The University of Texas at Dallas.

    A high-energy, nimble, innovative institution, UT Dallas offers top-ranked science, engineering and business programs and has gained prominence for a breadth of educational paths from audiology to arts and technology. UT Dallas’ faculty includes a Nobel laureate, six members of the National Academies and more than 560 tenured and tenure-track professors.

     
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