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    Skyrmion research: Braids of nanovortices discovered

    A team of scientists from Germany, Sweden and China has discovered a new physical phenomenon: complex braided structures made of tiny magnetic vortices known as skyrmions. Skyrmions were first detected experimentally a little over a decade ago and have since been the subject of numerous studies, as well as providing a possible basis for innovative concepts in information processing that offer better performance and lower energy consumption. Furthermore, skyrmions influence the magnetoresistive and thermodynamic properties of a material. The discovery therefore has relevance for both applied and basic research.
    Strings, threads and braided structures can be seen everywhere in daily life, from shoelaces, to woollen pullovers, from plaits in a child’s hair to the braided steel cables that are used to support countless bridges. These structures are also commonly seen in nature and can, for example, give plant fibres tensile or flexural strength. Physicists at Forschungszentrum Jülich, together with colleagues from Stockholm and Hefei, have discovered that such structures exist on the nanoscale in alloys of iron and the metalloid germanium.
    These nanostrings are each made up of several skyrmions that are twisted together to a greater or lesser extent, rather like the strands of a rope. Each skyrmion itself consists of magnetic moments that point in different directions and together take the form of an elongated tiny vortex. An individual skyrmion strand has a diamater of less than one micrometre. The length of the magnetic structures is limited only by the thickness of the sample; they extend from one surface of the sample to the opposite surface.
    Earlier studies by other scientists had shown that such filaments are largely linear and almost rod-shaped. However, ultra-high-resolution microscopy investigations undertaken at the Ernst Ruska-Centre in Jülich the theoretical studies at Jülich’s Peter Grünberg Institute have revealed a more varied picture: the threads can in fact twist together to varying degrees. According to the researchers, these complex shapes stabilise the magnetic structures, making them particularly interesting for use in a range of applications.
    “Mathematics contains a great variety of these structures. Now we know that this theoretical knowledge can be translated into real physical phenomena,” Jülich physicist Dr. Nikolai Kiselev is pleased to report. “These types of structures inside magnetic solids suggest unique electrical and magnetic properties. However, further research is needed to verify this.”
    To explain the discrepancy between these studies and previous ones, the researcher points out that analyses using an ultra-high-resolution electron microscope do not simply provide an image of the sample, as in the case of, for example, an optical microscope. This is because quantum mechanical phenomena come into play when the high energy electrons interact with those in the sample.
    “It is quite feasible that other researchers have also seen these structures under the microscope, but have been unable to interpret them. This is because it is not possible to directly determine the distribution of magnetization directions in the sample from the data obtained. Instead, it is necessary to create a theoretical model of the sample and to generate a kind of electron microscope image from it,” explains Kiselev. “If the theoretical and experimental images match, one can conclude that the model is able to represent reality.” In ultra-high-resolution analyses of this kind, Forschungszentrum Jülich with its Ernst Ruska-Centre counts as one of the leading institutions worldwide.
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    Brain cell differences could be key to learning in humans and AI

    The new study found that by tweaking the electrical properties of individual cells in simulations of brain networks, the networks learned faster than simulations with identical cells.
    They also found that the networks needed fewer of the tweaked cells to get the same results, and that the method is less energy intensive than models with identical cells.
    The authors say that their findings could teach us about why our brains are so good at learning, and might also help us to build better artificially intelligent systems, such as digital assistants that can recognise voices and faces, or self-driving car technology.
    First author Nicolas Perez, a PhD student at Imperial College London’s Department of Electrical and Electronic Engineering, said: “The brain needs to be energy efficient while still being able to excel at solving complex tasks. Our work suggests that having a diversity of neurons in both brains and AI systems fulfils both these requirements and could boost learning.”
    The research is published in Nature Communications.
    Why is a neuron like a snowflake?
    The brain is made up of billions of cells called neurons, which are connected by vast ‘neural networks’ that allow us to learn about the world. Neurons are like snowflakes: they look the same from a distance but on further inspection it’s clear that no two are exactly alike. More

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    Intelligence emerging from random polymer networks

    Reservoir computing (RC) tackles complex problems by mimicking the way information is processed in animal brains. It relies on a randomly connected network that serves as a reservoir for information and ultimately leads to more efficient outputs. For realizing RC directly in matter (instead of simulating it in a digital computer), numerous reservoir materials have been investigated to date. Now a team including researchers from Osaka University has designed a sulfonated polyaniline network for RC.
    Neural networks in the brain use electrochemical signals carried by ions. Therefore, an electrochemical approach is a logical choice when choosing a material system for RC. Organic electrochemical field-effect transistors (OECFETs) are popular in bioelectronics; however, they have not yet been widely used for RC.
    The key to the reservoir material is that it has rich (time-dependent) behavior and is disordered, which makes polymer materials an excellent option as they form random networks by themselves.
    Polyaniline is a promising polymer for RC applications, because it is easy to polymerize, has good stability in the atmosphere, and has reversible doping/de-doping behavior, which means its conduction can be altered.
    The researchers investigated sulfonated polyaniline (SPAN), which, in addition to the advantages of polyaniline, has high water-solubility and self-doping behavior. These make SPAN easier to work with and the doping more uniform.
    “Atmospheric protons are injected directly into the polymer chain of SPAN, which causes it to conduct,” explains study lead author Yuki Usami. “This conduction can then be controlled by adjusting the humidity.”
    The researchers used a simple drop-casting method to assemble the SPAN on gold electrodes to give an organic electrochemical network device (OEND).
    The SPAN OEND was tested for RC by checking the waveform and assessing its performance in short-term memory tasks. Results of a test to see how well speech could be recognized achieved 70% accuracy. This ability of SPAN OEND was comparable with a software simulation of RC.
    “We have shown that our SPAN OEND system can be applied in RC,” says study corresponding author Takuya Matsumoto. “Future steps to establish systems that do not rely on humidity will provide more practical options; however, the success of our SPAN-based system is a positive step for material-based reservoir computing, which is expected to have a significant impact on the next generation of artificial intelligence devices.”
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    Blockchain technology could provide secure communications for robot teams

    Imagine a team of autonomous drones equipped with advanced sensing equipment, searching for smoke as they fly high above the Sierra Nevada mountains. Once they spot a wildfire, these leader robots relay directions to a swarm of firefighting drones that speed to the site of the blaze.
    But what would happen if one or more leader robots was hacked by a malicious agent and began sending incorrect directions? As follower robots are led farther from the fire, how would they know they had been duped?
    The use of blockchain technology as a communication tool for a team of robots could provide security and safeguard against deception, according to a study by researchers at MIT and Polytechnic University of Madrid, which was published today in IEEE Transactions on Robotics. The research may also have applications in cities where multirobot systems of self-driving cars are delivering goods and moving people across town.
    A blockchain offers a tamper-proof record of all transactions — in this case, the messages issued by robot team leaders — so follower robots can eventually identify inconsistencies in the information trail.
    Leaders use tokens to signal movements and add transactions to the chain, and forfeit their tokens when they are caught in a lie, so this transaction-based communications system limits the number of lies a hacked robot could spread, according to Eduardo Castelló, a Marie Curie Fellow in the MIT Media Lab and lead author of the paper.
    “The world of blockchain beyond the discourse about cryptocurrency has many things under the hood that can create new ways of understanding security protocols,” Castelló says. More

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    Smuggling light through opaque materials

    Electrical engineers at Duke University have discovered that changing the physical shape of a class of materials commonly used in electronics and near- and mid-infrared photonics — chalcogenide glasses — can extend their use into the visible and ultraviolet parts of electromagnetic spectrum. Already commercially used in detectors, lenses and optical fibers, chalcogenide glasses may now find a home in applications such as underwater communications, environmental monitoring and biological imaging.
    The results appear online on October 5 in the journal Nature Communications.
    As the name implies, chalcogenide glasses contain one or more chalcogens — chemical elements such as sulfur, selenium and tellurium. But there’s one member of the family they leave out: oxygen. Their material properties make them a strong choice for advanced electronic applications such as optical switching, ultra-small direct laser writing (think tiny rewritable CDs) and molecular fingerprinting. But because they strongly absorb wavelengths of light in the visible and ultraviolet parts of electromagnetic spectrum, chalcogenide glasses have long been constrained to the near- and mid-infrared with respect to their applications in photonics.
    “Chalcogenides have been used in the near- and mid-IR for a long time, but they’ve always had this fundamental limitation of being lossy at visible and UV wavelengths,” said Natalia Litchinitser, professor of electrical and computer engineering at Duke. “But recent research into how nanostructures affect the way these materials respond to light indicated that there might be a way around these limitations.”
    In recent theoretical research into the properties of gallium arsenide (GaAs), a semiconductor commonly used in electronics, Litchinitser’ s collaborators, Michael Scalora of the US Army CCDC Aviation and Missile Center and Maria Vincenti of the University of Brescia predicted that nanostructured GaAs might respond to light differently than its bulk or even thin film counterparts. Because of the way that high intensity optical pulses interact with the nanostructured material, very thin wires of the material lined up next to one another might create higher-order harmonic frequencies (shorter wavelengths) that could travel through them.
    Imagine a guitar string that is tuned to resonate at 256 Hertz — otherwise known as middle C. The researchers were proposing that if fabricated just right, this string when plucked might also vibrate at frequencies one or two octaves higher in small amounts. More

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    New type of magnetism unveiled in an iconic material

    Scientists have made a path-breaking discovery in strontium ruthenate — with potential for new applications in quantum electronics.
    Since the discovery of superconductivity in Sr2RuO4 in 1994, hundreds of studies have been published on this compound, which have suggested that Sr2RuO4 is a very special system with unique properties. These properties make Sr2RuO4 a material with great potential, for example, for the development of future technologies including superconducting spintronics and quantum electronics by virtue of its ability to carry lossless electrical currents and magnetic information simultaneously. An international research team led by scientists at the University of Konstanz has been now able to answer one of the most interesting open questions on Sr2RuO4: why does the superconducting state of this material exhibit some features that are typically found in materials known as ferromagnets, which are considered being antagonists to superconductors? The team has found that Sr2RuO4 hosts a new form of magnetism, which can coexist with superconductivity and exists independently of superconductivity as well. The results have been published in the current issue of Nature Communications.
    After a research study that lasted several years and involved 26 researchers from nine different universities and research institutions, the missing piece of the puzzle seems to have been found. Alongside the University of Konstanz, the universities of Salerno, Cambridge, Seoul, Kyoto and Bar Ilan as well as the Japan Atomic Energy Agency, the Paul Scherrer Institute and the Centro Nazionale delle Ricerche participated in the study.
    So far not the right tool to find evidence
    “Despite decades of research on Sr2RuO4, there had been no evidence for the existence of this unusual type of magnetism in this material. A few years ago, however, we wondered if the reconstruction that happens in this material on the surface, where the crystal structure exhibits some small changes at the atomic scale level, could also lead to an electronic ordering with magnetic properties. Following this intuition, we realized that this question had probably not been addressed because nobody had used the “right tool” to find evidence for this magnetism, which we thought could be extremely weak and only limited to a few atomic layers from the surface of the material” states the leader of this international research study, Professor Angelo Di Bernardo from the University of Konstanz, whose research focuses on superconducting spintronic and quantum devices based on innovative materials.
    To carry out the experiment, the team used high-quality single crystals of Sr2RuO4 prepared by the group of Dr Antonio Vecchione from the Centro Nazionale delle Ricerche (CNR) Spin in Salerno. “Making large crystals of Sr2RuO4 without any impurities was a big challenge albeit crucial for the success of the experiment, since defects would have given a signal similar to the magnetic signal which we were hunting,” says Dr Vecchione. More

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    A robot that finds lost items

    A busy commuter is ready to walk out the door, only to realize they’ve misplaced their keys and must search through piles of stuff to find them. Rapidly sifting through clutter, they wish they could figure out which pile was hiding the keys.
    Researchers at MIT have created a robotic system that can do just that. The system, RFusion, is a robotic arm with a camera and radio frequency (RF) antenna attached to its gripper. It fuses signals from the antenna with visual input from the camera to locate and retrieve an item, even if the item is buried under a pile and completely out of view.
    The RFusion prototype the researchers developed relies on RFID tags, which are cheap, battery-less tags that can be stuck to an item and reflect signals sent by an antenna. Because RF signals can travel through most surfaces (like the mound of dirty laundry that may be obscuring the keys), RFusion is able to locate a tagged item within a pile.
    Using machine learning, the robotic arm automatically zeroes-in on the object’s exact location, moves the items on top of it, grasps the object, and verifies that it picked up the right thing. The camera, antenna, robotic arm, and AI are fully integrated, so RFusion can work in any environment without requiring a special set up.
    While finding lost keys is helpful, RFusion could have many broader applications in the future, like sorting through piles to fulfill orders in a warehouse, identifying and installing components in an auto manufacturing plant, or helping an elderly individual perform daily tasks in the home, though the current prototype isn’t quite fast enough yet for these uses.
    “This idea of being able to find items in a chaotic world is an open problem that we’ve been working on for a few years. Having robots that are able to search for things under a pile is a growing need in industry today. Right now, you can think of this as a Roomba on steroids, but in the near term, this could have a lot of applications in manufacturing and warehouse environments,” said senior author Fadel Adib, associate professor in the Department of Electrical Engineering and Computer Science and director of the Signal Kinetics group in the MIT Media Lab. More

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    Work on complex systems, including Earth’s climate, wins the physics Nobel Prize

    Earth’s climate is a vastly complex system on a grand scale. On a microscopic level, so is the complicated physics of atoms and molecules found within materials. The 2021 Nobel Prize in physics knits together the work of three scientists who illuminated such intricate physical systems by harnessing basic tools of physics. 

    Half of the prize goes to climate scientists Syukuro Manabe of Princeton University and Klaus Hasselmann of the Max Planck Institute for Meteorology in Hamburg, Germany, for their work on simulations of Earth’s climate and predictions of global warming, the Royal Swedish Academy of Sciences announced October 5. The other half of the 10 million Swedish kronor (more than $1.1 million) prize goes to physicist Giorgio Parisi of Sapienza University of Rome, who worked on understanding the roiling fluctuations within disordered materials.

    All three researchers used a similar strategy of isolating a specific piece of a complex system in a model, a mathematical representation of something found in nature. By studying that model, and then integrating that understanding into more complicated descriptions, the researchers made progress on understanding otherwise perplexing systems, says physicist Brad Marston of Brown University. “There’s an art to constructing a model that is rich enough to give you interesting and perhaps surprising results, but simple enough that you can hope to understand it.”

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    The prize, normally an apolitical affair, sends a message to world leaders: “The notion of global warming is resting on solid science,” said Göran Hansson, secretary-general of the Royal Swedish Academy of Sciences, during the announcement of the prize winners. Human emissions of greenhouse gases, including carbon dioxide, have increased Earth’s average temperature by more than 1 degree Celsius since preindustrial times. That warming is affecting every region on Earth, exacerbating extreme weather events such as heat waves, wildfires and drought (SN: 8/9/21). 

    Syukuro Manabe of Princeton University (left) and Klaus Hasselmann of the Max Planck Institute for Meteorology (right) worked on early simulations of Earth’s climate, laying the foundation for today’s more detailed climate models that are used to grapple with the potential impacts of global warming.From left: Bengt Nyman/Wikimedia Commons (CC BY 2.0); Sueddeutsche Zeitung Photo/Alamy Stock Photo

    Manabe’s work laid the foundation for climate modeling, said John Wettlaufer of Yale University, a member of the Nobel Committee for Physics. “He really did construct the models from which all future climate models were built,” Wettlaufer explained during an interview after the prize announcement. “That scaffolding is essential for the improvement of predictions of climate.” 

    Manabe studied how rising carbon dioxide levels would change temperatures on Earth. A simplified climate model from a 1967 paper coauthored by Manabe simulated a single column of the atmosphere in which air masses rise and fall as they warm and cool, which revealed that doubling the amount of carbon dioxide in the atmosphere increased the temperature by over 2 degrees C. This understanding could then be integrated into more complex models that simulated the entire atmosphere or included the effects of the oceans, for example (SN: 5/30/70). 

    “I never imagined that this thing I would begin to study had such huge consequences,” Manabe said at a news conference at Princeton. “I was doing it just because of my curiosity.”

    Hasselmann studied the evolution of Earth’s climate while taking into account the variety of timescales over which different processes operate. The randomness of daily weather stands in contrast to seasonal variations and much slower processes like gradual heating of the Earth’s oceans. Hassleman’s work helped to show how the short-term jitter could be incorporated into models to understand the long-term change in climate. 

    Giorgio Parisi of Sapienza University of Rome is known for his work delving into the physics of disordered materials, such as spin glasses, in which different atoms can’t come to agreement about which direction to point their spins. Lorenza Parisi/Wikimedia Commons

    The prize is an affirmation of scientists’ understanding of climate, says Michael Moloney, CEO of the American Institute of Physics in College Park, Md. “The climate models which we depend on in order to understand the impact of the climate crisis are world-class science up there with all the other great discoveries that are recognized [by] Nobel Prizes of years past.”

    In a spin glass, illustrated here, iron atoms (red), within a lattice of copper atoms (blue), have spins (black arrows) that can’t agree on a direction to point.C. Chang

    Much like the weather patterns on Earth, the inner world of atoms within materials can be complex and disorderly. Parisi’s work took aim at understanding the processes within disordered systems such as a type of material called a spin glass (SN: 10/18/02). In spin glasses, atoms behave like small magnets, due to a quantum property called spin. But the atoms can’t agree on which direction to point their magnets, resulting in a disordered arrangement.

    That’s similar to more familiar types of glass — a material in which atoms don’t reach an orderly arrangement. Parisi came up with a mathematical description for such spin glasses. His work also touches on a variety of other complex topics, from turbulence to flocking patterns that describe the motions of animals such as starlings (SN: 7/31/14). 

    Although his work doesn’t directly focus on climate, in an interview during the Nobel announcement, Parisi commented on that half of the prize: “It’s clear that for the future generation we have to act now in a very fast way.” 

    Carolyn Gramling contributed to reporting this story. More