Aurelia Butler

Researchers at North Carolina State University have demonstrated a caterpillar-like soft robot that can move forward, backward and dip under narrow spaces. The caterpillar-bot’s movement is driven by a novel pattern of silver nanowires that use heat to control the way the robot bends, allowing users to steer the robot in either direction.
“A caterpillar’s movement is controlled by local curvature of its body — its body curves differently when it pulls itself forward than it does when it pushes itself backward,” says Yong Zhu, corresponding author of a paper on the work and the Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State. “We’ve drawn inspiration from the caterpillar’s biomechanics to mimic that local curvature, and use nanowire heaters to control similar curvature and movement in the caterpillar-bot.
“Engineering soft robots that can move in two different directions is a significant challenge in soft robotics,” Zhu says. “The embedded nanowire heaters allow us to control the movement of the robot in two ways. We can control which sections of the robot bend by controlling the pattern of heating in the soft robot. And we can control the extent to which those sections bend by controlling the amount of heat being applied.”
The caterpillar-bot consists of two layers of polymer, which respond differently when exposed to heat. The bottom layer shrinks, or contracts, when exposed to heat. The top layer expands when exposed to heat. A pattern of silver nanowires is embedded in the expanding layer of polymer. The pattern includes multiple lead points where researchers can apply an electric current. The researchers can control which sections of the nanowire pattern heat up by applying an electric current to different lead points, and can control the amount of heat by applying more or less current.
“We demonstrated that the caterpillar-bot is capable of pulling itself forward and pushing itself backward,” says Shuang Wu, first author of the paper and a postdoctoral researcher at NC State. “In general, the more current we applied, the faster it would move in either direction. However, we found that there was an optimal cycle, which gave the polymer time to cool — effectively allowing the ‘muscle’ to relax before contracting again. If we tried to cycle the caterpillar-bot too quickly, the body did not have time to ‘relax’ before contracting again, which impaired its movement.”
The researchers also demonstrated that the caterpillar-bot’s movement could be controlled to the point where users were able steer it under a very low gap — similar to guiding the robot to slip under a door. In essence, the researchers could control both forward and backward motion as well as how high the robot bent upwards at any point in that process.
“This approach to driving motion in a soft robot is highly energy efficient, and we’re interested in exploring ways that we could make this process even more efficient,” Zhu says. “Additional next steps include integrating this approach to soft robot locomotion with sensors or other technologies for use in various applications — such as search-and-rescue devices.”
The work was done with support from the National Science Foundation, under grants 2122841, 2005374 and 2126072; and from the National Institutes of Health, under grant number 1R01HD108473. More

Artificial muscles are a progressing technology that could one day enable robots to function like living organisms. Such muscles open up new possibilities for how robots can shape the world around us; from assistive wearable devices that can redefine our physical abilities at old age, to rescue robots that can navigate rubble in search of the missing. But just because artificial muscles can have a strong societal impact during use, doesn’t mean they have to leave a strong environmental impact after use.
The topic of sustainability in soft robotics has now been brought into focus by an international team of researchers from the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart (Germany), the Johannes Kepler University (JKU) in Linz (Austria), and the University of Colorado (CU Boulder), Boulder (USA). The scientists collaborated to design a fully biodegradable, high performance artificial muscle — based on gelatin, oil, and bioplastics. They show the potential of this biodegradable technology by using it to animate a robotic gripper, which could be especially useful in single-use deployments such as for waste collection. At the end of life, these artificial muscles can be disposed of in municipal compost bins; under monitored conditions, they fully biodegrade within six months.
“We see an urgent need for sustainable materials in the accelerating field of soft robotics. Biodegradable parts could offer a sustainable solution especially for single-use applications, like for medical operations, search-and-rescue missions, and manipulation of hazardous substances. Instead of accumulating in landfills at the end of product life, the robots of the future could become compost for future plant growth,” says Ellen Rumley, a visiting scientist from CU Boulder working in the Robotic Materials Department at MPI-IS. Rumley is co-first author of the paper “Biodegradable electrohydraulic actuators for sustainable soft robots” which will be published in Science Advances on March 22, 2023.
Specifically, the team of researchers built an electrically driven artificial muscle called HASEL. In essence, HASELs are oil-filled plastic pouches that are partially covered by a pair of electrical conductors called electrodes. Applying a high voltage across the electrode pair causes opposing charges to build on them, generating a force between them that pushes oil to an electrode-free region of the pouch. This oil migration causes the pouch to contract, much like a real muscle. The key requirement for HASELs to deform is that the materials making up the plastic pouch and oil are electrical insulators, which can sustain the high electrical stresses generated by the charged electrodes.
One of the challenges for this project was to develop a conductive, soft, and fully biodegradable electrode. Researchers atJohannes Kepler University created a recipe based on a mixture of biopolymer gelatin and salts that can be directly cast onto HASEL actuators. “It was important for us to make electrodes suitable for these high-performance applications, but with readily available components and an accessible fabrication strategy. Since our presented formulation can be easily integrated in various types of electrically driven systems, it serves as a building block for future biodegradable applications,” states David Preninger, co-first author for this project and a scientist at the Soft Matter Physics Division at JKU.
The next step was finding suitable biodegradable plastics. Engineers for this type of materials are mainly concerned with properties like degradation rate or mechanical strength, not with electrical insulation; a requirement for HASELs that operate at a few thousand Volts. Nonetheless, some bioplastics showed good material compatibility with gelatin electrodes and sufficient electrical insulation. HASELs made from one specific material combination were even able to withstand 100,000 actuation cycles at several thousand Volts without signs of electrical failure or loss in performance. These biodegradable artificial muscles are electromechanically competitive with their non-biodegradable counterparts; an exciting result for promoting sustainability in artificial muscle technology.
“By showing the outstanding performance of this new materials system, we are giving an incentive for the robotics community to consider biodegradable materials as a viable material option for building robots,” Ellen Rumley continues. “The fact that we achieved such great results with bio-plastics hopefully also motivates other material scientists to create new materials with optimized electrical performance in mind.”
With green technology becoming ever more present, the team’s research project is an important step towards a paradigm shift in soft robotics. Using biodegradable materials for building artificial muscles is just one step towards paving a future for sustainable robotic technology. More

The push toward truly autonomous vehicles has been hindered by the cost and time associated with safety testing, but a new system developed at the University of Michigan shows that artificial intelligence can reduce the testing miles required by 99.99%.
It could kick off a paradigm shift that enables manufacturers to more quickly verify whether their autonomous vehicle technology can save lives and reduce crashes. In a simulated environment, vehicles trained by artificial intelligence perform perilous maneuvers, forcing the AV to make decisions that confront drivers only rarely on the road but are needed to better train the vehicles.
To repeatedly encounter those kinds of situations for data collection, real world test vehicles need to drive for hundreds of millions to hundreds of billions of miles.
“The safety critical events — the accidents, or the near misses — are very rare in the real world, and often time AVs have difficulty handling them,” said Henry Liu, U-M professor of civil engineering and director of both Mcity and the Center for Connected and Automated Transportation, a regional transportation research center funded by the U.S. Department of Transportation.
U-M researchers refer to the problem as the “curse of rarity,” and they’re tackling it by learning from real-world traffic data that contains rare safety-critical events. Testing conducted on test tracks mimicking urban as well as highway driving showed that the AI-trained virtual vehicles can accelerate the testing process by thousands of times. The study appears on the cover of Nature.
“The AV test vehicles we’re using are real, but we’ve created a mixed reality testing environment. The background vehicles are virtual, which allows us to train them to create challenging scenarios that only happen rarely on the road,” Liu said.

U-M’s team used an approach to train the background vehicles that strips away nonsafety-critical information from the driving data used in the simulation. Basically, it gets rid of the long spans when other drivers and pedestrians behave in responsible, expected ways — but preserves dangerous moments that demand action, such as another driver running a red light.
By using only safety-critical data to train the neural networks that make maneuver decisions, test vehicles can encounter more of those rare events in a shorter amount of time, making testing much cheaper.
“Dense reinforcement learning will unlock the potential of AI for validating the intelligence of safety-critical autonomous systems such as AVs, medical robotics and aerospace systems,” said Shuo Feng, assistant professor in the Department of Automation at Tsinghua University and former assistant research scientist at the U-M Transportation Research Institute.
“It also opens the door for accelerated training of safety-critical autonomous systems by leveraging AI-based testing agents, which may create a symbiotic relationship between testing and training, accelerating both fields.”
And it’s clear that training, along with the time and expense involved, is an impediment. An October Bloomberg article stated that although robotaxi leader Waymo’s vehicles had driven 20 million miles over the previous decade, far more data was needed.
“That means,” the author wrote, “its cars would have to drive an additional 25 times their total before we’d be able to say, with even a vague sense of certainty, that they cause fewer deaths than bus drivers.”
Testing was conducted at Mcity’s urban environment in Ann Arbor, as well as the highway test track at the American Center for Mobility in Ypsilanti.
Launched in 2015, Mcity, was the world’s first purpose-built test environment for connected and autonomous vehicles. With new support from the National Science Foundation, outside researchers will soon be able to run remote, mixed reality tests using both the simulation and physical test track, similar to those reported in this study.
Real-world data sets that support Mcity simulations are collected from smart intersections in Ann Arbor and Detroit, with more intersections to be equipped. Each intersection is fitted with privacy-preserving sensors to capture and categorize each road user, identifying its speed and direction. The research was funded by the Center for Connected and Automated Transportation and the National Science Foundation. More

A model system created by stacking a pair of monolayer semiconductors is giving physicists a simpler way to study confounding quantum behavior, from heavy fermions to exotic quantum phase transitions.
The group’s paper, “Gate-Tunable Heavy Fermions in a Moiré Kondo Lattice,” published March 15 in Nature. The lead author is postdoctoral fellow Wenjin Zhao in the Kavli Institute at Cornell.
The project was led by Kin Fai Mak, professor of physics in the College of Arts and Sciences, and Jie Shan, professor of applied and engineering physics in Cornell Engineering and in A&S, the paper’s co-senior authors. Both researchers are members of the Kavli Institute; they came to Cornell through the provost’s Nanoscale Science and Microsystems Engineering (NEXT Nano) initiative.
The team set out to address what is known as the Kondo effect, named after Japanese theoretical physicist Jun Kondo. About six decades ago, experimental physicists discovered that by taking a metal and substituting even a small number of atoms with magnetic impurities, they could scatter the material’s conduction electrons and radically alter its resistivity.
That phenomenon puzzled physicists, but Kondo explained it with a model that showed how conduction electrons can “screen” the magnetic impurities, such that the electron spin pairs with the spin of a magnetic impurity in opposite directions, forming a singlet.
While the Kondo impurity problem is now well understood, the Kondo lattice problem — one with a regular lattice of magnetic moments instead of random magnetic impurities — is much more complicated and continues to stump physicists. Experimental studies of the Kondo lattice problem usually involve intermetallic compounds of rare earth elements, but these materials have their own limitations.

“When you move all the way down to the bottom of the Periodic Table, you end up with something like 70 electrons in an atom,” Mak said. “The electronic structure of the material becomes so complicated. It is very difficult to describe what’s going on even without Kondo interactions.”
The researchers simulated the Kondo lattice by stacking ultrathin monolayers of two semiconductors: molybdenum ditelluride, tuned to a Mott insulating state, and tungsten diselenide, which was doped with itinerant conduction electrons. These materials are much simpler than bulky intermetallic compounds, and they are stacked with a clever twist. By rotating the layers at a 180-degree angle, their overlap results in a moiré lattice pattern that traps individual electrons in tiny slots, similar to eggs in an egg carton.
This configuration avoids the complication of dozens of electrons jumbling together in the rare earth elements. And instead of requiring chemistry to prepare the regular array of magnetic moments in the intermetallic compounds, the simplified Kondo lattice only needs a battery. When a voltage is applied just right, the material is ordered into forming a lattice of spins, and when one dials to a different voltage, the spins are quenched, producing a continuously tunable system.
“Everything becomes much simpler and much more controllable,” Mak said.
The researchers were able to continuously tune the electron mass and density of the spins, which cannot be done in a conventional material, and in the process they observed that the electrons dressed with the spin lattice can become 10 to 20 times heavier than the “bare” electrons, depending on the voltage applied.
The tunability can also induce quantum phase transitions whereby heavy electrons turn into light electrons with, in between, the possible emergence of a “strange” metal phase, in which electrical resistance increases linearly with temperature. The realization of this type of transition could be particularly useful for understanding the high-temperature superconducting phenomenology in copper oxides.
“Our results could provide a laboratory benchmark for theorists,” Mak said. “In condensed matter physics, theorists are trying to deal with the complicated problem of a trillion interacting electrons. It would be great if they don’t have to worry about other complications, such as chemistry and material science, in real materials. So they often study these materials with a ‘spherical cow’ Kondo lattice model. In the real world you cannot create a spherical cow, but in our material now we’ve created one for the Kondo lattice.”
Co-authors include doctoral students Bowen Shen and Zui Tao; postdoctoral researchers Kaifei Kang and Zhongdong Han; and researchers from the National Institute for Materials Science in Tsukuba, Japan.
The research was primarily supported by the Air Force Office of Scientific Research, the National Science Foundation, the U.S. Department of Energy and the Gordon and Betty Moore Foundation. More

Physicists at Delft University of Technology have built a new technology on a microchip by combining two Nobel Prize-winning techniques for the first time. This microchip could measure distances in materials at high precision, for example underwater or for medical imaging. Because the technology uses sound vibrations instead of light, it is useful for high-precision position measurements in opaque materials. The instrument could lead to new techniques to monitor the Earth’s climate and human health. The work is now published in Nature Communications.
Simple and low-power technology
The microchip mainly consists of a thin ceramic sheet that is shaped like a trampoline. This trampoline is patterned with holes to enhance its interaction with lasers and has a thickness about 1000 times smaller than the thickness of a hair. As a former PhD candidate in Richard Norte’s lab, Matthijs de Jong studied the small trampolines to figure out what would happen if they pointed a simple laser beam at them. The trampoline’s surface started vibrating intensely. By measuring the reflected laser light from the vibrating surface, the team noticed a pattern of vibrations in the shape of a comb that they hadn’t seen before. They realised that the trampoline’s comb-like signature functions as a ruler for precision measurements of distance.
This new technology could be used to measure positions in materials using sound waves. What makes it special is that it doesn’t need any precision hardware and is therefore easy to produce. “It only requires inserting a laser, and nothing else. There’s no need for complex feedback loops or for tuning certain parameters to get our tech to operate properly. This makes it a very simple and low-power technology, that is much easier to miniaturise on a microchip,” Norte says. “Once this happens, we could really put these microchip sensors anywhere, given their small size.”
Unique combination
The new technology is based on two unrelated Nobel Prize-winning techniques, called optical trapping and frequency combs. Norte: “The interesting thing is that both of these concepts are typically related to light, but these fields do not have any real overlap. We have uniquely combined them to create an easy-to-use microchip technology based on sound waves. This ease of use could have significant implications for how we measure the world around us.”
Overtones
When the researchers pointed a laser beam at the tiny trampoline, they realised that the forces that the laser exerted on it were creating overtone vibrations in the trampoline membranes. “These forces are called an optical trap, because they can trap particles in one spot using light. This technique won the Nobel Prize in 2018 and it allows us to manipulate even the smallest particles with extreme precision,” Norte explains. “You can compare the overtones in the trampoline to particular notes of a violin. The note or frequency that the violin produces depends on where you place your finger on the string. If you touch the string only very lightly and play it with a bow, you can create overtones; a series of notes at higher frequencies. In our case, the laser acts as both the soft touch and the bow to induce overtone vibrations in the trampoline membrane.”
Bridging two breakthrough fields
“Optical frequency combs are used in labs around the world for very precise measurements of time, and to measure distances,” Norte says. “They are so important to measurements in general that their invention was given a Nobel Prize in 2005. We have made an acoustic version of a frequency comb, made out of sound vibrations in the membrane instead of light. Acoustic frequency combs could for instance make position measurements in opaque materials, through which vibrations can propagate better than light waves. This technology could for example be used for precision measurements underwater to monitor the Earth’s climate, for medical imaging and for applications in quantum technologies.” More

Scientists investigating a compound called “Y-ball” – which belongs to a mysterious class of “strange metals” viewed as centrally important to next-generation quantum materials – have found new ways to probe and understand its behavior.
The results of the experiments, aided by the insights of theoretical physicists at Rutgers, could play a role in the development of revolutionary technologies and devices.
“It’s likely that that quantum materials will drive the next generation of technology and that strange metals will be part of that story,” said Piers Coleman, a Distinguished Professor at the Rutgers Center for Materials Theory in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences and one of the theoreticians involved in the study. “We know that strange metals like Y-ball exhibit properties that need to be understood to develop these future applications. We’re pretty sure that understanding this strange metal will give us new ideas and will help us design and discover new materials.”
Reporting in the journal Science, an international team of researchers from Rutgers, the University of Hyogo and the University of Tokyo in Japan, the University of Cincinnati and Johns Hopkins University described details of electron motion that provide new insight into the unusual electrical properties of Y-ball. The material, technically known as the compound YbAlB4, contains the elements ytterbium, aluminum and boron. It was nicknamed “Y-ball” by the late Elihu Abrahams, founding director of the Rutgers Center for Materials Theory.
The experiment revealed unusual fluctuations in the strange metal’s electrical charge. The work is groundbreaking, the researchers said, because of the novel way the experimenters examined Y-ball, firing gamma rays at it using a synchrotron, a type of particle accelerator.
The Rutgers team — including Coleman, fellow physics professor Premala Chandra and former postdoctoral fellow Yashar Komijani (now an assistant professor at the University of Cincinnati) — have spent years exploring the mysteries of strange metals. They do so through the framework of quantum mechanics, the physical laws governing the realm of the ultra-small, home of the building blocks of nature such as electrons.

Analyzing the material using a technique known as Mossbauer spectroscopy, the scientists probed Y-ball with gamma rays, measuring the rate at which the strange metal’s electrical charge fluctuates. In a conventional metal, as they move, electrons hop in and out of the atoms, causing their electrical charge to fluctuate, but at a rate that is thousands of times too fast to be seen by Mossbauer spectroscopy. In this case, the change happened in a nanosecond, a billionth of a second.
“In the quantum world, a nanosecond is an eternity,” said Komijani. “For a long time, we have been wondering why these fluctuations are actually so slow.” “We reasoned,” continued Chandra, “that each time an electron hops into an ytterbium atom, it stays there long enough to attract the surrounding atoms, causing them to move in and out. This synchronized dance of the electrons and atoms slows the whole process so that it can be seen by the Mossbauer.”
They moved to the next step. “We asked the experimentalists to look for these vibrations,” said Komijani, “and to our delight, they detected them.”
Coleman explained that when an electrical current flows through conventional metals, such as copper, random atomic motion scatters the electrons causing friction called resistance. As the temperature is raised, the resistance increases in a complex fashion and at some point it reaches a plateau.
In strange metals such as Y-ball, however, resistance increases linearly with temperature, a much simpler behavior. In addition, further contributing to their “strangeness,” when Y-ball and other strange metals are cooled to low temperatures, they often become superconductors, exhibiting no resistance at all.
The materials with the highest superconducting temperatures fall into this strange family. These metals are thus very important because they provide the canvas for new forms of electronic matter — especially exotic and high temperature superconductivity.
Superconducting materials are expected to be central to the next generation of quantum technologies because, in eliminating all electrical resistance, they allow an electric current to flow in a quantum mechanically synchronized fashion. The researchers see their work as opening a door to future, perhaps unimaginable possibilities.
“In the 19th century, when people were trying to figure out electricity and magnetism, they couldn’t have imagined the next century, which was entirely driven by that understanding,” Coleman said. “And so, it’s also true today, that when we use the vague phrase ‘quantum materials,’ we can’t really envisage how it will transform the lives of our grandchildren.” More

In our daily lives, lithium-ion batteries have become indispensable. They function only because of a passivation layer that forms during their initial cycle. As researchers at Karlsruhe Institute of Technology (KIT) found out via simulations, this solid electrolyte interphase develops not directly at the electrode but aggregates in the solution. The scientists report on their study in the Advanced Energy Materials journal. Their findings allow the optimization of the performance and lifetime of future batteries.
From smartphones to electric cars — wherever a mobile energy source is required, it is almost always a lithium-ion battery that does the job. An essential part of the reliable function of this and other liquid electrolyte batteries is the solid electrolyte interphase (SEI). This passivation layer forms when voltage is applied for the first time. The electrolyte is being decomposed in the immediate vicinity of the surface. Until now, it remained unclear ow the particles in the electrolytes form a layer that is up to 100 nanometers thick on the surface of the electrode since the decomposition reaction is only possible in a few nanometers distance from the surface.
The passivation layer on the anode surface is crucial to the electrochemical capacity and lifetime of a lithium-ion battery because it is highly stressed with every charging cycle. When the SEI is broken up during this process, the electrolyte is further decomposed and the battery’s capacity is reduced — a process that determines the lifetime of a battery. With the right knowledge on the SEI’s growth and composition, the properties of a battery can be controlled. But so far, no experimental or computer-aided approach was sufficient to decipher the SEI’s complex growth processes that take place on a very wide scale and in different dimensions.
Study as Part of the EU Initiative BATTERY 2030+
Researchers at the KIT Institute of Nanotechnology (INT) now managed to characterize the formation of the SEI with a multi-scale approach. “This solves one of the great mysteries regarding an essential part of all liquid electrolyte batteries — especially the lithium-ion batteries we all use every day,” says Professor Wolfgang Wenzel, director of the research group “Multiscale Materials Modelling and Virtual Design” at INT, which is involved in the large-scale European research initiative BATTERY 2030+ that aims to develop safe, affordable, long-lasting, sustainable high-performance batteries for the future. The KIT researchers report on their findings in the journal Advanced Energy Materials.
More than 50,000 Simulations for Different Reaction Conditions
To examine the growth and composition of the passivation layer at the anode of liquid electrolyte batteries, the researchers at INT generated an ensemble of over 50,000 simulations representing different reaction conditions. They found that the growth of the organic SEI follows a solution-mediated pathway: First, SEI precursors that are formed directly at the surface join far away from the electrode surface via a nucleation process. The subsequent rapid growth of the nuclei leads to the formation of a porous layer that eventually covers the electrode surface. These findings offer a solution to the paradoxical situation that SEI constituents can form only near the surface, where electrons are available, but their growth would stop once this narrow region is covered. “We were able to identify the key reaction parameters that determine SEI thickness,” explains Dr. Saibal Jana, postdoc at INT and one of the authors of the study. “This will enable the future development of electrolytes and suitable additives that control the properties of the SEI and optimize the battery’s performance and lifetime.” (or) More

In 2019, an international research team headed by materials chemist Anna Isaeva, at that time a junior professor at ct.qmat (Complexity and Topology in Quantum Matter), caused a stir by fabricating the world’s first antiferromagnetic topological insulator — manganese bismuth telluride (MnBi2Te4). This remarkable material has its own internal magnetic field, paving the way for new kinds of electronic components that can store information magnetically and transport it on the surface without any resistance. This could revolutionize computers by making them more sustainable and energy-efficient. Since then, researchers around the globe have been actively studying various aspects of this promising quantum material, eager to unlock its full potential.
Milestone achieved with MnBi6Te10
Based on the previously discovered MnBi2Te4, a team from ct.qmat has now engineered a topological insulator with ferromagnetic properties known as MnBi6Te10. In ferromagnetic materials, the individual manganese atoms are magnetically aligned in parallel, meaning that all their magnetic moments point in the same direction. By contrast, in its antiferromagnetic predecessor, MnBi2Te4, only the magnetic moments within a single layer of the material are aligned in this way. The slight change in the crystal’s chemical composition has a major impact, as the ferromagnetic topological insulator MnBi6Te10 exhibits a stronger and more robust magnetic field than its antiferromagnetic predecessor. “We managed to fabricate the quantum material MnBi6Te10 such that it becomes ferromagnetic at 12 Kelvin. Although this temperature of -261 degrees Celsius is still far too low for computer components, this is the first step on the long journey of development,” explains Professor Vladimir Hinkov from Würzburg. It was his group who discovered that the material’s surface exhibits ferromagnetic properties, enabling it to conduct current without any loss, whereas its interior doesn’t share this characteristic.
Race for the miracle material
The ct.qmat research team wasn’t alone in aiming to create a ferromagnetic topological insulator in the laboratory. “Following the remarkable success of MnBi2Te4, researchers worldwide began searching for more candidates for magnetic topological insulators. In 2019, four different groups synthesized MnBi6Te10, but it was only in our lab that this extraordinary material displayed ferromagnetic properties,” explains Isaeva, now a professor of experimental physics at the University of Amsterdam.
Antisite disorder in the atomic structure
When the Dresden-based materials chemists led by Isaeva painstakingly figured out how to produce the crystalline material in a process akin to detective work, they made an astonishing discovery. It turned out that some atoms needed to be repositioned from their original atomic layer, meaning they had to leave their native arrangement in the crystal. “The distribution of manganese atoms across all crystal layers causes the surrounding manganese atoms to rotate their magnetic moment in the same direction. The magnetic order becomes contagious,” explains Isaeva. “Atomic antisite disorder, the phenomenon seen in our crystal, is usually considered disruptive in chemistry and physics. Ordered atomic structures are easier to calculate and better understood — yet they don’t always yield the desired result,” adds Hinkov. “This very disorder is the critical mechanism that enables MnBi6Te10 to become ferromagnetic,” emphasizes Isaeva.
Collaborative network for cutting-edge research
ct.qmat scientists from the two universities TU Dresden and JMU Würzburg as well as from the Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW) in Dresden collaborated on this groundbreaking research. The crystals were prepared by a team of materials chemists headed by Isaeva (TU Dresden). Subsequently, the samples’ bulk ferromagnetism was detected at IFW, where Dr. Jorge I. Facio also developed a comprehensive theory explaining both the ferromagnetism of MnBi6Te10 characterized by antisite disorder and its antiferromagnetic counterparts. Hinkov’s team at JMU Würzburg conducted the vital surface measurements.
The researchers are currently working to achieve ferromagnetism at considerably higher temperatures. They’ve already made initial progress, reaching around 70 Kelvin. Simultaneously, the ultra-low temperatures at which the exotic quantum effects manifest need to be increased, as lossless current conduction only starts at 1 to 2 Kelvin.
Cluster of Excellence ct.qmat
The Cluster of Excellence ct.qmat — Complexity and Topology in Quantum Matter has been jointly run by Julius-Maximilians-Universität Würzburg and Technische Universität Dresden since 2019. Nearly 400 scientists from more than 30 countries and from four continents study topological quantum materials that reveal surprising phenomena under extreme conditions such as ultra-low temperatures, high pressure, or strong magnetic fields. ct.qmat is funded through the German Excellence Strategy of the Federal and State Governments and is the only Cluster of Excellence to be based in two different federal states. More