Computers Math

Computational detective work by U.S. and German physicists has confirmed cerium zirconium pyrochlore is a 3D quantum spin liquid.
Despite the name, quantum spin liquids are solid materials in which quantum entanglement and the geometric arrangement of atoms frustrate the natural tendency of electrons to magnetically order themselves in relation to one another. The geometric frustration in a quantum spin liquid is so severe that electrons fluctuate between quantum magnetic states no matter how cold they become.
Theoretical physicists routinely work with quantum mechanical models that manifest quantum spin liquids, but finding convincing evidence that they exist in actual physical materials has been a decadeslong challenge. While a number of 2D or 3D materials have been proposed as possible quantum spin liquids, Rice University physicist Andriy Nevidomskyy said there’s no established consensus among physicists that any of them qualify.
Nevidomskyy is hoping that will change based on the computational sleuthing he and colleagues from Rice, Florida State University and the Max Planck Institute for Physics of Complex Systems in Dresden, Germany, published this month in the open-access journal npj Quantum Materials.
“Based on all the evidence we have today, this work confirms that the single crystals of the cerium pyrochlore identified as candidate 3D quantum spin liquids in 2019 are indeed quantum spin liquids with fractionalized spin excitations,” he said.
The inherent property of electrons that leads to magnetism is spin. Each electron behaves like a tiny bar magnet with a north and south pole, and when measured, individual electron spins always point up or down. In most everyday materials, spins point up or down at random. But electrons are antisocial by nature, and this can cause them to arrange their spins in relation to their neighbors in some circumstances. In magnets, for example, spins are collectively arranged in the same direction, and in antiferromagnets they are arranged in an up-down, up-down pattern. More

Settling a key dispute in the wireless communications field, researchers at the National Institute of Standards and Technology (NIST) found that transmission performance is consistent across different bands of the millimeter-wave (mmWave) spectrum targeted for high-speed, data-rich 5G systems.
Wireless systems are moving to the mmWave spectrum at 10-100 gigahertz (GHz), above crowded cellular frequencies as well as early 5G systems around 3 GHz. System operators tend to prefer lower bands of the new mmWave spectrum. One reason is that they are influenced by a formula that says more signals are lost at higher frequencies due to smaller wavelengths resulting in a smaller useful antenna area. But until now, measurements of this effect by many organizations have disagreed over whether this is true.
NIST researchers developed a new method to measure frequency effects, using the 26.5-40 GHz band as a target example. After extensive study in the laboratory and two real-world environments, NIST results confirmed that the main signal path — over a clear “line of sight” between transmitter and receiver — does not vary by frequency, a generally accepted thesis for traditional wireless systems but until now not proven for the mmWave spectrum. The results are described in a new paper.
The team also found that signal losses in secondary paths — where transmissions are reflected, bent or diffused into clusters of reflections — can vary somewhat by frequency, depending on the type of path. Reflective paths, which are the second strongest and critical for maintaining connectivity, lost only a little signal strength at higher frequencies. The weaker bent and diffuse paths lost a bit more. Until now, the effects of frequency on this so-called multipath were unknown.
“This work may serve to demyth many misconceptions about propagation about higher frequencies in 5G and 6G,” NIST electrical engineer Camillo Gentile said. “In short, while performance will be worse at higher frequencies, the drop in performance is incremental. So we do expect the deployment at 5G and eventually at 6G to be successful.”
The NIST method emphasizes innovative measurement procedures and enhanced equipment calibration to make sure only the transmission channel is measured. The researchers used NIST’s SAMURAI (Synthetic Aperture Measurement UnceRtainty for Angle of Incidence) channel sounder, which supports design and repeatable testing of 5G mmWave devices with unprecedented accuracy across a wide range of signal frequencies and scenarios. The NIST system is unique in that antenna beams can be steered in any direction for precise angle-of-arrival estimates.
NIST’s main innovations in the new study, as discussed in the paper, were calibration procedures to remove the effects of channel sounder equipment from the measurements, extension of an existing algorithm to determine from a single measurement how individual paths vary by frequency, and studies in an industrial control center and a conference room to classify the types of paths involved and determine any frequency effects.
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Materials provided by National Institute of Standards and Technology (NIST). Note: Content may be edited for style and length. More

An intermediate layer consisting of a few atoms is helping to improve the transport of spin currents from one material to another. Until now, this process involves significant losses. A team from Martin Luther University Halle-Wittenberg (MLU), the Max Planck Institute (MPI) for Microstructure Physics, and the Freie Universität Berlin reports in the scientific journal ACS Nano Letters on how this can be avoided. The researchers thus demonstrate important new insights relevant for many spintronic applications, for example energy-efficient and ultra-fast storage technologies of the future.
In modern microelectronics, the charge of electrons is used to carry information in electronic components, mobile phones and storage media. The charge transport requires a relatively large amount of energy and generates heat. Spintronics could offer an energy-saving alternative. The basic idea is to utilise spin in information processing. Spin is the intrinsic angular momentum of the electrons that creates a magnetic moment. This generates the magnetism that will ultimately be used to process information.
In spintronics, spin currents also have to be transferred from one material to the next. “In many cases, the spin transport across interfaces is a very lossy process,” explains physicist Professor Georg Woltersdorf from MLU, who led the study. The team looked for a way to mitigate these losses by using an approach that, at first, sounds rather contradictory: they integrated an insulating barrier between the two materials. “We designed the insulator at the atomic level so that it turned metallic and could conduct the spin currents. This enabled us to significantly improve the spin transport and optimise the interfacial properties,” says Woltersdorf, summing up the process. The material samples were produced at the Max Planck Institute for Microstructure Physics. The unexpected effect was discovered through measurements of spin transport conducted at MLU and the Freie Universität Berlin. The team also provides the theoretical basis for the new discovery. According to Woltersdorf, this can be described using relatively simple models without spin-orbit coupling.
The results are highly relevant for many spintronic applications. For example, they can be used to improve spintronic terahertz emitters. Terahertz radiation is not not only applied in research, but also in high-frequency electronics, medicine, materials testing and communication technology.
The study was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) and the European Union.
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It’s hard to tell the difference between a newborn boy and girl based solely on temperament characteristics such as the baby’s propensity to display fear, smile or laugh. But once babies reach around a year old that begins to change.
A new study in PLOS ONE used machine learning to analyze temperament data on 4,438 babies in an attempt to classify the infants by gender and age.
The results indicate it is far easier for computer algorithms to determine the age of a baby than it is for them to decipher a baby’s gender based off temperament data during the infant’s first 48 weeks of life.
However, once the babies passed 48 weeks of age, gender classification improved for the multiple algorithms considered, suggesting gender differences in infancy become more accentuated around this time.
“It is at least suggestive of a picture where temperament begins to differentiate by gender in a more powerful way around age one,” said Maria Gartstein, lead author of the study and a professor of psychology at Washington State University.
Previous research has investigated age and gender-based temperament differences in babies, but few if any studies have looked at the two variables together. More

Fruit flies synchronize the movements of their heads and bodies to stabilize their vision and fly effectively, according to Penn State researchers who utilized virtual-reality flight simulators. The finding appears to hold true in primates and other animals, the researchers say, indicating that animals evolved to move their eyes and bodies independently to conserve energy and improve performance. This understanding could inform the design of advanced mobile robots, according to principal investigator Jean-Michel Mongeau, assistant professor of mechanical engineering.
The researchers published their results yesterday, May 3, in The Proceedings of the National Academy of Sciences.
“We discovered that when controlling gaze, fruit flies minimize energy expenditure and increase flight performance,” Mongeau said. “And, using that coordination information, we developed a mathematical model that accurately predicts similar synchronization in [other] visually active animals.”
Researchers used high-speed cameras to record a fruit fly surrounded by LED video screens upon which the researchers projected footage of what a fly would see while in flight, creating an immersive virtual-reality experience and causing the fly to move as if freely flying.
“When a fly moves, it coordinates its head, wings and body to fly through the air, evade predators or look for food,” Mongeau said. “We were interested in studying how flies coordinate these movements, and we did so by simulating flight in virtual reality.”
Responding to both slow and fast visual motion in the virtual-reality flight simulator, the fly moved its head and body at different rates. The researchers took measurements and tracked the fly’s head movements to determine the direction of its gaze, since its eyes are fixed to its head and cannot move independently. More

In a world of materials that normally expand upon heating, one that shrinks along one 3D axis while expanding along another stands out. That’s especially true when the unusual shrinkage is linked to a property important for thermoelectric devices, which convert heat to electricity or electricity to heat.
In a paper just published in the journal Advanced Materials, a team of scientists from Northwestern University and the U.S. Department of Energy’s Brookhaven National Laboratory describe the previously hidden sub-nanoscale origins of both the unusual shrinkage and the exceptional thermoelectric properties in this material, silver gallium telluride (AgGaTe2). The discovery reveals a quantum mechanical twist on what drives the emergence of these properties — and opens up a completely new direction for searching for new high-performance thermoelectrics.
“Thermoelectric materials will be transformational in green and sustainable energy technologies for heat energy harvesting and cooling — but only if their performance can be improved,” said Hongyao Xie, a postdoctoral researcher at Northwestern and first author on the paper. “We want to find the underlying design principles that will allow us to optimize the performance of these materials,” Xie said.
Thermoelectric devices are currently used in limited, niche applications, including NASA’s Mars rover, where heat released by the radioactive decay of plutonium is converted into electricity. Future applications might include materials controlled by voltage to achieve very stable temperatures critical for operation of high-tech optical detectors and lasers.
The main barrier to wider adoption is the need for materials with just the right cocktail of properties, including good electrical conductivity but resistance to the flow of heat.
“The trouble is, these desirable properties tend to compete,” said Mercouri Kanadzidis, the Northwestern professor who initiated this study. “In most materials, electronic conductivity and thermal conductivity are coupled and both are either high or low. Very few materials have the special high-low combination.”
Under certain conditions, silver gallium telluride appears to have just the right stuff — highly mobile conducting electrons and ultra-low thermal conductivity. In fact, its thermal conductivity is significantly lower than theoretical calculations and comparisons with similar materials such as copper gallium telluride would suggest. More

Imagine a computer that can think as fast as the human brain while using very little energy. That’s the goal of scientists seeking to discover or develop materials that can send and process signals as easily as the brain’s neurons and synapses. Identifying quantum materials with an intrinsic ability to switch between two distinct forms (or more) may hold the key to these futuristic sounding “neuromorphic” computing technologies.
In a paper just published in the journal Physical Review X, Yimei Zhu, a physicist at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, and his collaborators describe surprising new details about vanadium dioxide, one of the most promising neuromorphic materials. Using data collected by a unique “stroboscopic camera,” the team captured the hidden trajectory of atomic motion as this material transitions from an insulator to a metal in response to a pulse of light. Their findings could help guide the rational design of high-speed and energy-efficient neuromorphic devices.
“One way to reduce energy consumption in artificial neurons and synapses for brain-inspired computing is to exploit the pronounced non-linear properties of quantum materials,” said Zhu. “The principal idea behind this energy efficiency is that, in quantum materials, a small electrical stimulus may produce a large response that can be electrical, mechanical, optical, or magnetic through a change of material state.”
“Vanadium dioxide is one of the rare, amazing materials that has emerged as a promising candidate for neuro-mimetic bio-inspired devices,” he said. It exhibits an insulator-metal transition near room temperature in which a small voltage or current can produce a large change in resistivity with switching that can mimic the behavior of both neurons (nerve cells) and synapses (the connections between them).
“It goes from completely insulating, like rubber, to a very good metal conductor, with a resistivity change of 10,000 times or more,” Zhu said.
Those two very different physical states, intrinsic in the same material, could be encoded for cognitive computing. More

Researchers at the Department of Energy’s Oak Ridge National Laboratory are teaching microscopes to drive discoveries with an intuitive algorithm, developed at the lab’s Center for Nanophase Materials Sciences, that could guide breakthroughs in new materials for energy technologies, sensing and computing.
“There are so many potential materials, some of which we cannot study at all with conventional tools, that need more efficient and systematic approaches to design and synthesize,” said Maxim Ziatdinov of ORNL’s Computational Sciences and Engineering Division and the CNMS. “We can use smart automation to access unexplored materials as well as create a shareable, reproducible path to discoveries that have not previously been possible.”
The approach, published in Nature Machine Intelligence, combines physics and machine learning to automate microscopy experiments designed to study materials’ functional properties at the nanoscale.
Functional materials are responsive to stimuli such as heat or electricity and are engineered to support both everyday and emerging technologies, ranging from computers and solar cells to artificial muscles and shape-memory materials. Their unique properties are tied to atomic structures and microstructures that can be observed with advanced microscopy. However, the challenge has been to develop efficient ways to locate regions of interest where these properties emerge and can be investigated.
Scanning probe microscopy is an essential tool for exploring the structure-property relationships in functional materials. Instruments scan the surface of materials with an atomically sharp probe to map out the structure at the nanometer scale — the length of one billionth of a meter. They can also detect responses to a range of stimuli, providing insights into fundamental mechanisms of polarization switching, electrochemical reactivity, plastic deformation or quantum phenomena. Today’s microscopes can perform a point-by-point scan of a nanometer square grid, but the process can be painstakingly slow, with measurements collected over days for a single material.
“The interesting physical phenomena are often only manifested in a small number of spatial locations and tied to specific but unknown structural elements. While we typically have an idea of what will be the characteristic features of physical phenomena we aim to discover, pinpointing these regions of interest efficiently is a major bottleneck,” said former ORNL CNMS scientist and lead author Sergei Kalinin, now at the University of Tennessee, Knoxville. “Our goal is to teach microscopes to seek regions with interesting physics actively and in a manner much more efficient than performing a grid search.”
Scientists have turned to machine learning and artificial intelligence to overcome this challenge, but conventional algorithms require large, human-coded datasets and may not save time in the end. More