Secrets of skyrmions revealed

Why skyrmions could have a lot in common with glass and high-temperature superconductors

Spawned by the spins of electrons in magnetic materials, these tiny whirlpools behave like independent particles and could be the future of computing. Experiments with SLAC’s X-ray laser are revealing their secrets.

Scientists have known for a long time that magnetism is created by the spins of electrons lining up in certain ways. But about a decade ago, they discovered another astonishing layer of complexity in magnetic materials: Under the right conditions, these spins can form little vortexes or whirlpools that act like particles and move around independently of the atoms that spawned them.

The tiny whirlpools are called skyrmions, named after Tony Skyrme, the British physicist who predicted their existence in 1962. Their small size and sturdy nature – like knots that are hard to undo – have given rise to a rapidly expanding field devoted to understanding them better and exploiting their strange qualities.

“These objects represent some of the most sophisticated forms of magnetic order that we know about,” said Josh Turner, a staff scientist at the Department of Energy’s SLAC National Accelerator Laboratory and principal investigator with the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC.

Read more on the SLAC website

Images: Top: Images based on simulations show how three phases of matter, including skyrmions – tiny whirlpools created by the spins of electrons – can form in certain magnetic materials. They are stripes of electron spin (left); hexagonal lattices (right); and an in-between phase (center) that’s a mixture of the two. In this middle, glass-like state, skyrmions move very slowly, like cars in a traffic jam – one of several discoveries made in recent studies by scientists at SLAC, Stanford, Berkeley Lab and UC San Diego. Bottom: Patterns formed in a detector during experiments that explored fundamentals of skyrmion behavior at SLAC’s Linac Coherent Light Source X-ray free-electron laser.

Credit: Esposito et al., Applied Physics Letters, 2020

A new approach creates an exceptional single-atom catalyst for water splitting

Anchoring individual iridium atoms on the surface of a catalytic particle boosted its performance in carrying out a reaction that’s been a bottleneck for sustainable energy production.

A new way of anchoring individual iridium atoms to the surface of a catalyst increased its efficiency in splitting water molecules to record levels, scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University reported today.

It was the first time this approach had been applied to the oxygen evolution reaction, or OER ­–part of a process called electrolysis that uses electricity to split water into hydrogen and oxygen. If powered by renewable energy sources, electrolysis could produce fuels and chemical feedstocks more sustainably and reduce the use of fossil fuels. But the sluggish pace of OER has been a bottleneck to improving its efficiency so it can compete in the open market.

The results of this study could ease the bottleneck and open new avenues to observing and understanding how these single-atom catalytic centers operate under realistic working conditions, the research team said.

They published their results today in the Proceedings of the National Academy of Sciences.

Read more on the SLAC website

Image: An illustration depicts a new system developed at SLAC and Stanford that anchors individual iridium atoms to the surface of a catalyst, increasing its efficiency at splitting water to record levels. The eight-sided support structures, shaded in blue, each contain a single iridium atom (large blue spheres). The iridium atoms grab passing water molecules (floating above and to the left of them), and encourage them to react with each other, releasing oxygen molecules (above and to the right). This reaction, known as the oxygen evolution reaction or OER, plays a key role in producing sustainable fuels and chemicals.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

A powerful infrared technique broadens its horizons

Infrared light has the right energy range to probe many interesting material properties, including the vibrational modes of molecules and the way electrons interact with external photons. As devices get smaller and faster, the ability to study the way light and matter interact at the nanoscale will become crucial for the development of quantum and microelectronic technologies.

A powerful infrared method for probing such phenomena is called scattering-type scanning near-field optical microscopy (s-SNOM), which uses the tip of an atomic force microscope (AFM) to focus infrared light down to about 10 nm, below the wavelength of the light itself (i.e., below the diffraction limit). However, because of the elongated geometry of the AFM tip, oriented perpendicular to the sample, s-SNOM is less sensitive to features of interest that lie parallel to the sample surface.

“Probing in-plane responses at the subwavelength scale has been a long-time hurdle for the technique,” said Ziheng Yao, a former ALS doctoral fellow and co-first author of a Nature Communications paper that reports on a way around this hurdle. “With our results, we can get not only the the top view of the object, but also the side views.”

At ALS Beamline 2.4, the researchers used s-SNOM to study samples of sapphire and LiNbO3, two well-characterized, prototypical materials suitable for a proof-of-concept demonstration. Both have a property (the dielectric function) that varies along different in-plane crystal axes.

Read more on the ALS website

Image: Schematic of the s-SNOM nanospectroscopy setup and the crystal orientation of the sample (a, b, and c axes). Red arrow indicates the in-plane component of the incident light, kin-plane. Rotating the sample changes θ, the angle between kin-plane and the c-axis. Inset: Image of the gold disk on sapphire (m-cut Al2O3). Sdark and Sbright are the two locations were spectra were collected. Scale bar = 1 µm.

Credit: Xinzhong Chen and Ziheng Yao/Stony Brook University

When vibrations increase on cooling: Anti-freezing observed

An international team has observed an amazing phenomenon in a nickel oxide material during cooling: Instead of freezing, certain fluctuations actually increase as the temperature drops. Nickel oxide is a model system that is structurally similar to high-temperature superconductors. The experiment, which was carried out at the Advanced Light Source (ALS) in California, shows once again that the behaviour of this class of materials still holds surprises.

In virtually all matter, lower temperatures mean less movement of its microscopic components. The less heat energy is available, the less often atoms change their location or magnetic moments their direction: they freeze. An international team led by scientists from HZB and DESY has now observed for the first time the opposite behaviour in a nickel oxide material closely related to high-temperature superconductors. Fluctuations in this nickelate do not freeze on cooling, but become faster.

Read more on the HZB website

Image: The development of this speckle pattern over time reveals microsocopic fluctuations in the material.

Credit: © 10.1103/PhysRevLett.127.057001

Main Attraction: Scientists Create World’s Thinnest Magnet

The development of an ultrathin magnet that operates at room temperature could lead to new applications in computing and electronics – such as high-density, compact spintronic memory devices – and new tools for the study of quantum physics.

The ultrathin magnet, which was recently reported in the journal Nature Communications, could make big advances in next-gen memory devices, computing, spintronics, and quantum physics. It was discovered by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.

“We’re the first to make a room-temperature 2D magnet that is chemically stable under ambient conditions,” said senior author Jie Yao, a faculty scientist in Berkeley Lab’s Materials Sciences Division and associate professor of materials science and engineering at UC Berkeley.

“This discovery is exciting because it not only makes 2D magnetism possible at room temperature, but it also uncovers a new mechanism to realize 2D magnetic materials,” added Rui Chen, a UC Berkeley graduate student in the Yao Research Group and lead author on the study.

Read more on the ALS website

Image: Illustration of magnetic coupling in a cobalt-doped zinc-oxide monolayer. Red, blue, and yellow spheres represent cobalt, oxygen, and zinc atoms, respectively.

Credit: Berkeley Lab

Scientists uncover a different facet of fuel-cell chemistry

Solid oxide fuel cells (SOFCs) are a promising technology for cleanly converting chemical energy to electrical energy. But their efficiency depends on the rate at which solids and gases interact at the devices’ electrode surfaces. Thus, to explore ways to improve SOFC efficiency, an international team led by researchers from Berkeley Lab studied a model electrode material in a new way—by exposing a different facet of its crystal structure to oxygen gas at operating pressures and temperatures.

“We began by asking questions like, could different reaction rates be achieved from the same material, just by changing which surface the oxygen reacts with?” said Lane Martin, a faculty scientist in Berkeley Lab’s Materials Sciences Division. “We wanted to examine how the atomic configuration at specific surfaces of these materials makes a difference when it comes to reacting with the oxygen gas.”

Thin films of a common SOFC cathode material, La0.8Sr0.2Co0.2Fe0.8O3 (LSCF), were epitaxially grown to expose a surface that was oriented along a diagonal crystallographic plane. Electrochemical measurements on this atypical surface yielded oxygen reaction rates up to three times faster than those measured on the usual horizontal plane.

To better understand the mechanisms underlying this improvement, the researchers used Advanced Light Source (ALS) Beamline 9.3.2 to perform ambient-pressure spectroscopy experiments at high temperatures and in varying pressures of oxygen. The results, combined with first-principles calculations, revealed that different crystallographic planes stabilize different surface chemistries, even though the bulk chemistry of the films is identical.

Read more on the ALS website

Image: A model SOFC cathode material adsorbs oxygen molecules (purple spheres) at vacancy sites, an important step in the electrochemical reaction taking place in fuel cells. Ambient-pressure experiments at the ALS allowed measurement of the surface chemical and electronic interactions at high temperature so that researchers could “see” the adsorption of oxygen at it happens. Light blue = La, dark blue = Sr, red = lattice O or O2 molecules, purple = adsorbed O2 molecules.

Credit: Abel Fernandez/UC Berkeley

Artificial spin ice toggles twist in X-ray beams on demand

SCIENTIFIC ACHIEVEMENT

Advanced Light Source (ALS) studies helped scientists understand how a nanoscale magnetic lattice (an artifical spin ice) acts as a toggle switch for x-ray beams with spiral character.

SIGNIFICANCE AND IMPACT

The findings represent an important step toward the development of a versatile new tool for probing or controlling exotic phenomena in electronic and magnetic systems.

A curious singularity

Artificial spin ices (ASIs) are engineered arrays of nanomagnets that are often “frustrated,” meaning that the magnets, constrained by geometry, cannot align themselves to minimize their interaction energy. Water ice exhibits a similar property with regard to the positioning of hydrogen atoms.

While studying ASIs, a collaboration between scientists from the University of Kentucky and the ALS (see related feature article) made an interesting observation: light scattered from certain ASIs produced diffraction patterns in which spots of constructive interference were shaped like donuts instead of dots. The donuts were indicative of a phase singularity—a hallmark of light with a property known as orbital angular momentum (OAM).

Read more on the ALS website

Image: When x-rays are scattered from a patterned array of nanoscale magnets with a lattice defect, the beams acquire a spiral character (orbital angular momentum, or OAM) that produces diffraction patterns with donut-shaped spots. Researchers have found that these OAM beams can be switched on and off by adjusting the temperature or applying an external magnetic field.

Target selection for COVID-19 antibody therapeutics

SCIENTIFIC ACHIEVEMENT

Protein-structure studies at the Advanced Light Source (ALS) helped demonstrate that the primary target of antibody-based COVID-19 immunity is the part of the virus’s spike protein that can most easily mutate.

SIGNIFICANCE AND IMPACT

This work anticipated the rise of SARS-CoV-2 variants and guides the selection of antibody therapeutics that are likely to be more resistant to immune escape.

A better understanding of immunity

To better predict the course of the COVID-19 pandemic and to develop the best new therapeutics, researchers need to understand what regions of the SARS-CoV-2 virus are most critical to the immune response and how likely these regions are to mutate and evade immunity.

Two recent papers, relying in part on protein-structure studies at the ALS, have provided detailed information about the SARS-CoV-2 virus that causes COVID-19 and the human immune response to it. The results reveal where the virus surface protein is most likely to mutate, what the consequences of those mutations may be, and which types of antibodies may be the most effective therapeutics.

Read more on the ALS website

Image: Left: Composite model of the SARS-CoV-2 spike protein trimer with six mAbs shown bound to one RBD (Piccoli et al.). Right: The first RBD–ACE2 complex structure where the RBD is a variant, in this case N439K; the figure highlights a new interaction between the N439K residue and ACE2 (Thomson et al.).

How X-rays could make reliable, rapid COVID-19 tests a reality

Vaccines are turning the tide in the pandemic, but the risk of infection is still present in some situations. If you want to visit a friend, get on a plane, or go see a movie, there is no highly accurate, instant test that can tell you right then and there whether or not you have a SARS-CoV-2 infection. But new research from Lawrence Berkeley National Laboratory (Berkeley Lab) could help get reliable instant tests on the market.

A study led by Michal Hammel and Curtis D. Hodge suggests that a highly sensitive lateral flow assay – the same type of device used in home pregnancy tests – could be developed using pairs of rigid antibodies that bind to the SARS-CoV-2 nucleocapsid protein. Such a test would only require a small drop of mucus or saliva, could give results in 15 minutes, and could detect a COVID-19 infection one day before the onset of symptoms. Their work was published in the journal mABs.

The current gold standard tests for COVID-19 use a form of polymerase chain reaction (PCR) to identify the presence of SARS-CoV-2 nucleic acid (RNA) rather than a viral protein. They are quite accurate, with false negative rates ranging less then 5%  (depending primarily on the sampling site, sample type, and stage of infection). However, PCR tests must be sent away for analysis at an accredited lab.

Read more on the Berkeley Lab website

Image: Molecular models constructed from the X-ray data show different antibodies bound to the SARS-CoV-2 nucleocapsid protein (pink). The scientists determined that the linear arrangement (right) has higher detection sensitivity than the sandwich arrangement (left).

Credit: Berkeley Lab

A properly tailored tail boosts solar-cell efficiency

With the help of structural insights from the Advanced Light Source (ALS), researchers optimized the fit between organic and inorganic ions in a perovskite solar-cell material.

The work increased the material’s power-conversion efficiency and stability and opens up a new avenue for improving the current-carrier dynamics of a promising class of materials.

A photovoltaic rising star

To address the effects of global climate change, it’s essential that we capitalize on energy from the sun. However, although solar energy is freely available, it needs to be converted into usable electricity in a way that’s efficient, cost-effective, and commercially scalable.

Perovskites are high-performance inorganic semiconductors recognized as some of the most promising photovoltaic materials of the future. Perovskite films—thin, lightweight, and flexible—can be produced using low-cost solution-processing techniques, and their power-conversion efficiencies (PCEs) have rapidly risen to the brink of 30% in just 15 years, surpassing conventional silicon panels.

A structure with room to tinker

The most intriguing perovskite materials today are organic–inorganic hybrids. They have the general formula ABX3, in which the inorganic B and X ions form a framework of octahedral cages, and the organic A ions are located in the spaces between the cages.

Previously, it was thought that perovskite electronic performance mainly depended on the B and X electronic orbitals, and that A merely served a structural function. In this work, researchers showed that A-site organic ions with specially designed characteristics can increase charge-carrier mobility and power conversion efficiency while also improving device stability.

Read more on the ALS website

Image: Left: The basic structure of perovskite, a promising solar-cell material, has three types of sites, A (blue), B (gray), and X (purple). Right: By attaching organic tails to the interstitial “A” sites (and testing different linker lengths), researchers improved the material’s photovoltaic response.

A 1-Atom-Deep Look at a Water-Splitting Catalyst

X-ray experiments at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) revealed an unexpected transformation in a single atomic layer of a material that contributed to a doubling in the speed of a chemical reaction – the splitting of water into hydrogen and oxygen gases. This process is a first step in producing hydrogen fuel for applications such as electric vehicles powered by hydrogen fuel cells.

The research team, led by scientists at SLAC National Accelerator Laboratory, performed a unique X-ray technique and related analyses, pioneered at Berkeley Lab’s Advanced Light Source (ALS), to home in on the changes at the surface layer of the material. The ALS produces X-rays and other forms of intense light to carry out simultaneous experiments at dozens of beamlines.

Read more on the LBL website

Image: This illustration shows two possible types of surface layers for a catalyst that performs the water-splitting reaction, the first step in making hydrogen fuel: The gray surface is lanthanum oxide and the colorful surface is nickel oxide. A rearrangement of nickel oxide’s atoms while carrying out the reaction made it twice as efficient. Researchers hope to harness this phenomenon to make better catalysts. Lanthanum atoms are depicted in green, nickel atoms in blue, and oxygen atoms in red.

Credit: CUBE3D

Newly discovered photosynthesis enzyme yields evolutionary clues

Rubisco is one of the oldest carbon-fixing enzymes on the planet, taking CO2 from the atmosphere and fixing it into sugar for plants and other photosynthetic organisms. Form I (“form one”) rubisco goes back nearly 2.4 billion years and is a key focus of scientists studying the evolution of life as well as those seeking to develop bio-based fuels and renewable-energy technologies. A newly discovered form of rubisco—dubbed form I′ (“one prime”)—is thought to represent a missing link in the evolution of photosynthetic organisms, potentially providing clues as to how this enzyme changed the planet.

To learn how form I′ rubisco compares to other rubisco enzymes, researchers performed x-ray crystallography at Advanced Light Source (ALS) Beamline 8.2.2. Then, to capture how the enzyme’s structure changes during different states of activity, they applied small-angle x-ray scattering (SAXS) using Beamline 12.3.1 (SIBYLS). This combination of approaches enables scientists to construct unprecedented models of complex molecules as they appear in nature.

Read more on the ALS website

Image: A ribbon diagram (left) and molecular surface representation (right) of carbon-fixing form I′ rubisco, showing eight molecular subunits without the small subunits found in other forms of rubisco. An x-ray diffraction pattern of the enzyme, also generated by the research team, is in the background.

Credit: Henrique Pereira/Berkeley Lab

Experimental drug targets HIV in a novel way

SCIENTIFIC ACHIEVEMENT

Using the Advanced Light Source (ALS), researchers from Gilead Sciences Inc. solved the structure of an experimental HIV drug bound to a novel target: the capsid protein that forms a shield around the viral RNA.

SIGNIFICANCE AND IMPACT

The work could lead to a long-lasting treatment for HIV that overcomes the problem of drug resistance and avoids the need for burdensome daily pill-taking.

Progress in HIV treatment still needed

Over the past couple of decades, safe and effective treatment for HIV infection has turned what was once a death sentence into a chronic disease. Today, people on the latest HIV drugs have near-normal life expectancy.

However, many people are still living with multidrug-resistant HIV, unable to control their virus loads with currently available HIV drugs. The virus develops resistance when people take their pills inconsistently due to forgetfulness, side effects, or a complex schedule. To some, taking a pill every day is a burden: they schedule their lives around it for fear of missing a dose. To others, it is a stigma, as it makes it difficult to hide one’s HIV status from close friends and family.

Read more on the Advanced Light Source website

Image: An experimental small-molecule drug (GS-6207) targets the protein building blocks of the HIV capsid—a conical shell (colored red in this artistic rendering) that encloses and protects the viral RNA—making the virus unable to replicate in cells. Credit Advanced Light Source

A probe of light-harvesting efficiency at the nanoscale

SCIENTIFIC ACHIEVEMENT

Using time-resolved experiments at the Advanced Light Source (ALS), researchers found a way to count electrons moving back and forth across a model interface for photoelectrochemical cells.

SIGNIFICANCE AND IMPACT

The findings provide real-time, nanoscale insight into the efficiency of nanomaterial catalysts that help turn sunlight and water into fuel through artificial photosynthesis.

Solar-fuel tech goes for gold

In the search for clean-energy alternatives to fossil fuels, one promising solution relies on photoelectrochemical (PEC) cells: water-splitting, artificial-photosynthesis devices that turn sunlight and water into solar fuels such as hydrogen. In just a decade, researchers have achieved great progress in the development of PEC systems made of light-absorbing gold nanoparticles (NPs) attached to a semiconductor film of titanium dioxide (TiO2).

Read more on the Advanced Light Source website

Image: Laser pulses were used to excite electrons in gold nanoparticles (AuNPs) on a titanium dioxide (TiO2) substrate. X-ray pulses were used to count the electrons moving between the nanoparticles and the substrate. (Credit: Oliver Gessner/Berkeley Lab)

Unexpected rise in ferroelectricity as material thins

SCIENTIFIC ACHIEVEMENT

Researchers working at the Advanced Light Source (ALS) showed that hafnium oxide surprisingly exhibits enhanced ferroelectricity (reversible electric polarization) as it gets thinner.

SIGNIFICANCE AND IMPACT

The work shifts the focus of ferroelectric studies from more complex, problematic compounds to a simpler class of materials and opens the door to novel ultrasmall, energy-efficient electronics.

Ferroelectric lower limit?

Distortions in the atomic geometries of certain materials can lead to ferroelectricity—the presence of electric dipoles (charge separations) with switchable polarizations. The ability to control this polarization with an external voltage offers great promise for ultralow-power microprocessors and nonvolatile memory.

As electronic devices become smaller, however, the materials used to store and manipulate electronic data are being pushed to low-dimensional extremes. Properties that function reliably in bulk materials often diminish in ultrathin films just a few atomic units thick. Therefore, exploring the critical thickness limit in “polar” materials (i.e., materials having spontaneous electric polarization) is not only a fundamental issue for nanoscale ferroelectric research, it also has extensive implications for the future of high-density ferroelectric-based electronics.

Read more on Advanced Light Source (ALS) website

Image : A thin layer of hafnium oxide (two unit-cell thicknesses, or about 1 nm) has an electric polarization that’s reversible by an external electric field, making it attractive for use in next-generation low-power microelectronics.

Credit: Ella Maru Studio

A scalable platform for two-dimensional metals

SCIENTIFIC ACHIEVEMENT

Using a new method for stabilizing a two-dimensional (2D) metal on a large-area platform, researchers probed the origins of the material’s superconductivity at the Advanced Light Source (ALS).

SIGNIFICANCE AND IMPACT

The work represents a notable milestone in advancing 2D materials toward broad applications in topological computing, advanced optics, and molecular sensing.

Expanding the scientific palette

If you confine everyday metals to layers only a few atoms thick, they acquire new properties that are different from those exhibited by their more common bulk forms. The ability to synthesize such two-dimensional (2D) metals means that the range of materials available for novel uses can be expanded to different areas of the periodic table—providing a much richer “scientific palette” of properties for applications in topological computing, advanced optics, and molecular sensing.

Read more on the ALS website

Image: A confined layer of metal atoms (silver spheres) on a silicon carbide (SiC) substrate is capped by a layer of graphene, allowing for new forms of low-dimensional metals with unique properties. Gold spheres represent Cooper pairs, responsible for conventional superconductivity. 

Credit: Yihuang Xiong/Penn State