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

Scientists capture a ‘quantum tug’ between neighbouring water molecules

The work sheds light on the web of hydrogen bonds that gives water its strange properties, which play a vital role in many chemical and biological processes.

Water is the most abundant yet least understood liquid in nature. It exhibits many strange behaviors that scientists still struggle to explain. While most liquids get denser as they get colder, water is most dense at 39 degrees Fahrenheit, just above its freezing point. This is why ice floats to the top of a drinking glass and lakes freeze from the surface down, allowing marine life to survive cold winters. Water also has an unusually high surface tension, allowing insects to walk on its surface, and a large capacity to store heat, keeping ocean temperatures stable.

Now, a team that includes researchers from the Department of Energy’s SLAC National Accelerator Laboratory, Stanford University and Stockholm University in Sweden have made the first direct observation of how hydrogen atoms in water molecules tug and push neighbouring water molecules when they are excited with laser light. Their results, published in Nature today, reveal effects that could underpin key aspects of the microscopic origin of water’s strange properties and could lead to a better understanding of how water helps proteins function in living organisms.

Read more on the LCLS website

Image: For these experiments, the research team (left to right: Xiaozhe Shen, Pedro Nunes, Jie Yang and Xijie Wang) used SLAC’s MeV-UED, a high-speed “electron camera” that uses a powerful beam of electrons to detect subtle molecular movements in samples.

Credit: Dawn Harmer/SLAC National Accelerator Laboratory

First detailed look at how charge transfer distorts a molecule’s structure

Charge transfer is highly important in most areas of chemistry, including photosynthesis and other processes in living things. A SLAC X-ray laser study reveals how it works in a molecule whose lopsided response to light has puzzled scientists for nearly a decade.

When light hits certain molecules, it dislodges electrons that then move from one location to another, creating areas of positive and negative charge. This “charge transfer” is highly important in many areas of chemistry, in biological processes like photosynthesis and in technologies like semiconductor devices and solar cells.

Even though theories have been developed to explain and predict how charge transfer works, they have been validated only indirectly because of the difficulty of observing how a molecule’s structure responds to charge movements with the required atomic resolution and on the required ultrafast time scales.

In a new study, a research team led by scientists from Brown University, the Department of Energy’s SLAC National Accelerator Laboratory and the University of Edinburgh used SLAC’s X-ray free-electron laser to make the first direct observations of molecular structures associated with charge transfer in gas molecules hit with light.

Molecules of this gas, called N,N′-dimethylpiperazine or DMP, are normally symmetric, with a nitrogen atom at each end. Light can knock an electron out of a nitrogen atom, leaving a positively charged ion known as a “charge center.”

Read more on the SLAC website

Image: In experiments with SLAC’s X-ray free-electron laser, scientists knocked electrons out of a molecule known as DMP to make the first detailed observations of how a process called charge transfer affects its molecular structure. Left: DMP is normally symmetric. Center: When a pulse of light knocks an electron out of one of its nitrogen atoms (blue spheres), it leaves a positively charged ion known as a charge center, shown in pink. This creates a charge imbalance that shifts the positions of atoms. Right: But within three trillionths of a second, the charge redistributes itself between the two nitrogen atoms until it evens out and the molecule becomes symmetric again.

Credit: Greg Stewart/ SLAC National Accelerator Laboratory

Surprising behavior of a fatty acid enzyme with potential biofuel applications

Derived from microscopic algae, the rare, light-driven enzyme converts fatty acids into starting ingredients for solvents and fuels.

Although many organisms capture and respond to sunlight, it’s rare to find enzymes – proteins that promote chemical reactions in living things – that are driven by light. Scientists have identified only three so far. The newest one, discovered in 2017, is called fatty acid photodecarboxylase (FAP). Derived from microscopic algae, FAP uses blue light to convert fatty acids into hydrocarbons that are similar to those found in crude oil.

“A growing number of researchers envision using FAPs for green chemistry applications because they can efficiently produce important components of solvents and fuels, including gasoline and jet fuels.” says Martin Weik, the leader of a research group at the Institut de Biologie Structurale at the Université Grenoble Alpes.

Weik is one of the primary investigators in a new study that has captured the complex sequence of structural changes, or photocycle, that FAP undergoes in response to light, which drives this fatty acid transformation. Researchers had proposed a possible FAP photocycle, but the fundamental mechanism was not understood, partly because the process is so fast that it’s very difficult to measure. Specifically, scientists didn’t know how long it took FAP to split a fatty acid and release a hydrocarbon molecule.

Experiments at the Linac Coherent Light Source (LCLS) at the Department of Energy’s SLAC National Accelerator Laboratory helped answer many of these outstanding questions. The researchers described their results in Science.

Read more on the SLAC website

Image: A study using SLAC’s LCLS X-ray laser captured how light drives a series of complex structural changes in an enzyme called FAP, which catalyzes the transformation of fatty acids into starting ingredients for solvents and fuels. This drawing captures the starting state of the catalytic reaction. The dark green background represents the protein’s molecular structure. The enzyme’s light-sensing part, called the FAD cofactor, is shown at center right with its three rings absorbing a photon coming from bottom left. A fatty acid at upper left awaits transformation. The amino acid shown at middle left plays an important role in the catalytic cycle, and the red dot near the center is a water molecule.

Credit: Damien Sorigué/Université Aix-Marseille

Researchers capture how materials break apart following an extreme shock

Understanding how materials deform and catastrophically fail when impacted by a powerful shock is crucial in a wide range of fields, including astrophysics, materials science and aerospace engineering. But until recently, the role of voids, or tiny pores, in such a rapid process could not be determined, requiring measurements to be taken at millionths of a billionth of a second.

Now an international research team has used ultrabright X-rays to make the first observations of how these voids evolve and contribute to damage in copper following impact by an extreme shock. The team, including scientists from the University of Miami, the Department of Energy’s SLAC National Accelerator Laboratory and Argonne National Laboratory, Imperial College London and the universities of Oxford and York published their results in Science Advances.

“Whether these materials are in a satellite hit by a micrometeorite, a spacecraft entering the atmosphere at hypersonic speed or a jet engine exploding, they have to fully absorb all that energy without catastrophically failing,” says lead author James Coakley, an assistant professor of mechanical and aerospace engineering at the University of Miami. “We’re trying to understand what happens in a material during this type of extremely rapid failure. This  experiment is the first round of attempting to do that, by looking at how the material compresses and expands during deformation before it eventually breaks apart.”

Read more on the SLAC website

Image: To see how materials respond to intense stress, researchers shocked a copper sample with picosecond laser pulses and used X-ray laser pulses to track the copper’s deformation. They captured how the material’s atomic lattice first compressed and subsequently expanded,, creating pores, or voids, that grew, coalesced, and eventually fractured the material.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

New X-ray laser data system will process a million images a second

When upgrades to the X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory are complete, the powerful new machine will capture up to 1 terabyte of data per second; that’s a data rate equivalent to streaming about one thousand full-length movies in just a single second, and analyzing every frame of each movie as they zoom past in this super-fast-forward mode.

Data experts at the lab are finding ways to handle this massive amount of information as the Linac Coherent Light Source (LCLS) upgrades come on line over the next several years.

LCLS accelerates electrons to nearly the speed of light to generate extremely bright beams of X-rays. Those X-rays probe a sample such as a protein or a quantum material, and a detector captures a series of images that reveal the atomic motion of the sample in real time. By stringing together these images, chemists, biologists, and materials scientists can create molecular movies of events like how plants absorb sunlight, or how our drugs help fight disease.

Read more on the SLAC website

Image: Data rate comparisons

Credit: Greg Stewart/SLAC National Accelerator Laboratory

New versatile spectro-electrochemical cell

Equipment improves the investigation of materials for fuel cells, batteries and electrolysers

Fossil fuels are the main source of energy in the world. However, the search for clean, renewable, and cheap energy sources has intensified recently, especially with the growing consensus that the rise in the average temperature of the planet is caused by human action. In this context, electrochemical devices, which involve reactions for the transformation of chemical energy into electrical energy, appear as a viable option to fossil fuels.

Among those available are fuel cells and batteries, capable of converting the chemical energy of molecules into electrical energy and storing it, and electrolysers capable of converting low-cost molecules into more economically attractive molecules. Thus, to improve the performance of these electrochemical devices, it is essential to understand the processes that occur between their components, more precisely in the interaction between the electrodes and the electrolyte.

For this reason, researchers from the State University of Campinas (UNICAMP), in collaboration with researchers from the Brazilian Center for Research in Energy and Materials (CNPEM) and the Federal University of São Carlos (UFSCar), developed an electrochemical cell [1] with the objective to perform various types of in situ experiments. These experiments allow direct access to the dynamics of electrochemical reactions in real time and make it possible to understand the processes that occur in the system from an atomic and molecular point of view. Hence, it is possible to optimize the materials that are part of fuel cells, batteries and electrolysers mentioned, and also of devices such as supercapacitors and electrochemical sensors, among others.

Read more on the LNLS website

Image: Figure 1: A, B) Schematic drawings of the SEC: threaded lip (1); aperture for passing the radiation beam and, in the case of a photoelectrochemical experiment, to illuminate the electrode with a solar simulator or LEDs (2); window (3); O-rings (4, 5, 17); CE (6 16); SEC body – part 1 (7); chamber for the electrolyte, the CE and the RE (8); electrolyte inlet and outlet (9, 11, 13), WE inlet (10); RE inlet (12); RE (14); CE inlet (15); bolt (18); SEC body – part 2 (19); WE (20).

A new X-ray detector snaps 1,000 atomic-level pictures per second of nature’s ultrafast processes

The ePix10k detector is ready to advance science at SLAC’s Linac Coherent Light Source X-ray laser and at facilities around the world.

Scientists around the world use synchrotrons and X-ray lasers to study some of nature’s fastest processes. These machines generate very bright and short X-ray flashes that, like giant strobe lights, “freeze” rapid motions and allow researchers to take sharp snapshots and make movies of atoms buzzing around in a sample.

A new generation of X-ray detectors developed at the Department of Energy’s SLAC National Accelerator Laboratory, called ePix10k, can take up to 1,000 of these snapshots per second – almost 10 times more than previous generations – to make more efficient use of light sources that fire thousands of X-ray flashes per second. Compared to previous ePix and other detectors, this X-ray “camera” can also handle more X-ray intensity, is three times more sensitive and is available with higher resolution – up to 2 megapixels.

Read more on the SLAC website

Image: Four units of the ePix10k camera, ready to further X-ray science at SLAC’s Linac Coherent Light Source (LCLS) and facilities worldwide. The camera can capture up to 1,000 X-ray images per second, almost 10 times more than previous detector generations. (Christopher Kenney/SLAC National Accelerator Laboratory)

SLAC’s upgraded X-ray laser facility produces first light

Marking the beginning of the LCLS-II era, the first phase of the major upgrade comes online.

Menlo Park, Calif. — Just over a decade ago in April 2009, the world’s first hard X-ray free-electron laser (XFEL) produced its first light at the US Department of Energy’s SLAC National Accelerator Laboratory. The Linac Coherent Light Source (LCLS) generated X-ray pulses a billion times brighter than anything that had come before. Since then, its performance has enabled fundamental new insights in a number of scientific fields, from creating “molecular movies” of chemistry in action to studying the structure and motion of proteins for new generations of pharmaceuticals and replicating the processes that create “diamond rain” within giant planets in our solar system.

The next major step in this field was set in motion in 2013, launching the LCLS-II upgrade project to increase the X-ray laser’s power by thousands of times, producing a million pulses per second compared to 120 per second today. This upgrade is due to be completed within the next two years.

Today the first phase of the upgrade came into operation, producing an X-ray beam for the first time using one critical element of the newly installed equipment.

Read more on the SLAC website

Image: Over the past 18 months, the original LCLS undulator system was removed and replaced with two totally new systems that offer dramatic new capabilities .

Credit: (Andy Freeberg/Alberto Gamazo/SLAC National Accelerator Laboratory)

Looping X-rays to produce higher quality laser pulses

A proposed device could expand the reach of X-ray lasers, opening new experimental avenues in biology, chemistry, materials science and physics.BY ALI SUNDERMIER

Ever since 1960, when Theodore Maiman built the world’s first infrared laser, physicists dreamed of producing X-ray laser pulses that are capable of probing the ultrashort and ultrafast scales of atoms and molecules.

This dream was finally realized in 2009, when the world’s first hard X-ray free-electron laser (XFEL), the Linac Coherent Light Source (LCLS) at the Department of Energy’s SLAC National Accelerator Laboratory, produced its first light. One limitation of LCLS and other XFELs in their normal mode of operation is that each pulse has a slightly different wavelength distribution, and there can be variability in the pulse length and intensity. Various methods exist to address this limitation, including ‘seeding’ the laser at a particular wavelength, but these still fall short of the wavelength purity of conventional lasers.

Read more on the SLAC National Accelerator Laboratory website

Image: Schematic arrangement of the experiment. The researchers send an X-ray pulse from LCLS through a liquid jet, where it creates excited atoms that emit a pulse of radiation at one distinct color moving in the same direction. This pulse is reflected through a series of mirrors arranged in a crossed loop. The size of this loop is carefully set so that the pulse arrives back at the liquid jet at the same time as a second X-ray pulse from LCLS. This produces an even brighter laser pulse, which then takes the same loop. The process is repeated several times, and with each loop the laser pulse intensifies and becomes more coherent. During the last loop, one of the mirrors is quickly switched allowing this laser pulse to exit.

Credit: (Greg Stewart/SLAC National Accelerator Laboratory)

Breaking the link between a quantum material’s spin and orbital states

The advance opens a path toward a new generation of logic and memory devices that could be 10,000 times faster than today’s.

In designing electronic devices, scientists look for ways to manipulate and control three basic properties of electrons: their charge; their spin states, which give rise to magnetism; and the shapes of the fuzzy clouds they form around the nuclei of atoms, which are known as orbitals.

Until now, electron spins and orbitals were thought to go hand in hand in a class of materials that’s the cornerstone of modern information technology; you couldn’t quickly change one  without changing the other. But a study at the Department of Energy’s SLAC National Accelerator Laboratory shows that a pulse of laser light can dramatically change the spin state of one important class of materials while leaving its orbital state intact.

>Read more on the LCLS at SLAC website

Image: These balloon-and-disk shapes represent an electron orbital – a fuzzy electron cloud around an atom’s nucleus – in two different orientations. Scientists hope to someday use variations in the orientations of orbitals as the 0s and 1s needed to make computations and store information in computer memories, a system known as orbitronics. A SLAC study shows it’s possible to separate these orbital orientations from electron spin patterns, a key step for independently controlling them in a class of materials that’s the cornerstone of modern information technology.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

First direct look at how light excites electrons to kick off a chemical reaction

Light-driven reactions are at the heart of human vision, photosynthesis and solar power generation. Seeing the very first step opens the door to observing chemical bonds forming and breaking.

The first step in many light-driven chemical reactions, like the ones that power photosynthesis and human vision, is a shift in the arrangement of a molecule’s electrons as they absorb the light’s energy. This subtle rearrangement paves the way for everything that follows and determines how the reaction proceeds.
Now scientists have seen this first step directly for the first time, observing how the molecule’s electron cloud balloons out before any of the atomic nuclei in the molecule respond.

While this response has been predicted theoretically and detected indirectly, this is the first time it’s been directly imaged with X-rays in a process known as molecular movie-making, whose ultimate goal is to observe how both electrons and nuclei act in real time when chemical bonds form or break.

>Read more on the LCLS at SLAC website

Image: extract, full image here

Scientists observe ultrafast birth of free radicals in water

What they learned could lead to a better understanding of how ionizing radiation can damage material systems, including cells.

Understanding how ionizing radiation interacts with water—like in water-cooled nuclear reactors and other water-containing systems—requires glimpsing some of the fastest chemical reactions ever observed.

In a new study conducted at the Department of Energy’s SLAC National Accelerator Laboratory, researchers have witnessed for the first time the ultrafast proton transfer reaction following ionization of liquid water. The findings, published today in Science, are the result of a world-wide collaboration led by scientists at the DOE’s Argonne National Laboratory, Nanyang Technological University, Singapore (NTU Singapore) and the German research center DESY.

The proton transfer reaction is a process of great significance to a wide range of fields, including nuclear engineering, space travel and environmental remediation. This observation was made possible by the availability of ultrafast X-ray free electron laser pulses, and is basically unobservable by other ultrafast methods. While studying the fastest chemical reactions is interesting in its own right, this observation of water also has important practical implications.

>Read more on the LCLS at SLAC website

Image: X-rays capture the ultrafast proton transfer reaction in ionized liquid water, forming the hydroxyl radical (OH) and the hydronium (H3O+) ion. Credit: Argonne National Laboratory

Inventing a way to see attosecond electron motions with an X-ray laser

Called XLEAP, the new method will provide sharp views of electrons in chemical processes that take place in billionths of a billionth of a second and drive crucial aspects of life.

Researchers at the Department of Energy’s SLAC National Accelerator Laboratory have invented a way to observe the movements of electrons with powerful X-ray laser bursts just 280 attoseconds, or billionths of a billionth of a second, long.

The technology, called X-ray laser-enhanced attosecond pulse generation (XLEAP), is a big advance that scientists have been working toward for years, and it paves the way for breakthrough studies of how electrons speeding around molecules initiate crucial processes in biology, chemistry, materials science and more.
The team presented their method today in an article in Nature Photonics.

“Until now, we could precisely observe the motions of atomic nuclei, but the much faster electron motions that actually drive chemical reactions were blurred out,” said SLAC scientist James Cryan, one of the paper’s lead authors and an investigator with the Stanford PULSE Institute, a joint institute of SLAC and Stanford University. “With this advance, we’ll be able to use an X-ray laser to see how electrons move around and how that sets the stage for the chemistry that follows. It pushes the frontiers of ultrafast science.”

Image: A SLAC-led team has invented a method, called XLEAP, that generates powerful low-energy X-ray laser pulses that are only 280 attoseconds, or billionths of a billionth of a second, long and that can reveal for the first time the fastest motions of electrons that drive chemistry. This illustration shows how the scientists use a series of magnets to transform an electron bunch (blue shape at left) at SLAC’s Linac Coherent Light Source into a narrow current spike (blue shape at right), which then produces a very intense attosecond X-ray flash (yellow).
Credit: Greg Stewart/SLAC National Accelerator Laboratory

>Read more on the Linear Coherent Light Source (SLAC) website

Breaking up buckyballs is hard to do

A new study shows how soccer ball-shaped molecules burst more slowly than expected when blasted with an X-ray laser beam.

As reported in Nature Physics, an international research team observed how soccer ball-shaped molecules made of carbon atoms burst in the beam of an X-ray laser. The molecules, called buckminsterfullerenes – buckyballs for short ­– consist of 60 carbon atoms arranged in alternating pentagons and hexagons like the leather coat of a soccer ball. These molecules were expected to break into fragments after being bombarded with photons, but the researchers watched in real time as buckyballs resisted the attack and delayed their break-up.

The team was led by Nora Berrah, a professor at the University of Connecticut, and included researchers from the Department of Energy’s SLAC National Accelerator Laboratory and the Deutsches Elektronen-Synchrotron (DESY) in Germany. The researchers focused their attention on examining the role of chemical effects, such as chemical bonds and charge transfer, on the buckyball’s fragmentation.

Using X-ray laser pulses from SLAC’s Linac Coherent Light Source (LCLS), the team showed how the bursting process, which takes only a few hundred femtoseconds, or millionths of a billionth of a second, unfolds over time. The results will be important for the analysis of sensitive proteins and other biomolecules, which are also frequently studied using bright X-ray laser flashes, and they also strengthen confidence in protein analysis with X-ray free-electron lasers (XFELs).

>Read more on the Linear Coherent Light Source at SLAC website

Image: An illustration shows how soccer ball-shaped molecules called buckyballs ionize and break up when blasted with an X-ray laser. A team of experimentalists and theorists identified chemical bonds and charge transfers as crucial factors that significantly delayed the fragmentation process by about 600 millionths of a billionth of a second.
Credit: Greg Stewart/SLAC National Accelerator Laboratory

For additional information: article published on the DESY website

The role of ‘charge stripes’ in superconducting materials

The studies could lead to a new understanding of how high-temperature superconductors operate.

High-temperature superconductors, which carry electricity with zero resistance at much higher temperatures than conventional superconducting materials, have generated a lot of excitement since their discovery more than 30 years ago because of their potential for revolutionizing technologies such as maglev trains and long-distance power lines. But scientists still don’t understand how they work.
One piece of the puzzle is the fact that charge density waves – static stripes of higher and lower electron density running through a material – have been found in one of the major families of high-temperature superconductors, the copper-based cuprates. But do these charge stripes enhance superconductivity, suppress it or play some other role?
In independent studies, two research teams report important advances in understanding how charge stripes might interact with superconductivity. Both studies were carried out with X-rays at the Department of Energy’s SLAC National Accelerator Laboratory.

>Read more on the LCLS at SLAC website

Image: This cutaway view shows stripes of higher and lower electron density – “charge stripes” – within a copper-based superconducting material. Experiments with SLAC’s X-ray laser directly observed how those stripes fluctuate when hit with a pulse of light, a step toward understanding how they interact with high-temperature superconductivity.
Credit: Greg Stewart/SLAC National Accelerator Laboratory