In 2016, the study of ferroelectrics got more interesting with the discovery of polar vortices — essentially spiral-shaped groupings of atoms — within the structure of the material. Now a team of researchers led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory has uncovered new insights into the behavior of these vortices, insights that may be the first step toward using them for fast, versatile data processing and storage.

What is so important about the behavior of groups of atoms in these materials? For one thing, these polar vortices are intriguing new discoveries, even when they are just sitting still. For another, this new research, published as a cover story in Nature, reveals how they move. This new type of spiral-patterned atomic motion can be coaxed into occurring, and can be manipulated. That’s good news for this material’s potential use in future data processing and storage devices.

“Although the motion of individual atoms alone may not be too exciting, these motions join together to create something new — an example of what scientists refer to as emergent phenomena — which may host capabilities we could not imagine before,” said Haidan Wen, a physicist in Argonne’s X-ray Science Division (XSD).

These vortices are indeed small — about five or six nanometers wide, thousands of times smaller than the width of a human hair, or about twice as wide as a single strand of DNA. Their dynamics, however, cannot be seen in a typical laboratory environment. They need to be excited into action by applying an ultrafast electric field.

All of which makes them difficult to observe and to characterize. Wen and his colleague, John Freeland, a senior physicist in Argonne’s XSD, have spent years studying these vortices, first with the ultrabright X-rays of the Advanced Photon Source (APS) at Argonne, and most recently with the free-electron laser capabilities of the LINAC Coherent Light Source (LCLS) at DOE’s SLAC National Accelerator Laboratory. Both the APS and LCLS are DOE Office of Science User Facilities.

Using the APS, researchers were able to use lasers to create a new state of matter and obtain a comprehensive picture of its structure using X-ray diffraction. In 2019, the team, led jointly by Argonne and The Pennsylvania State University, reported their findings in a Nature Materials cover story, most notably that the vortices can be manipulated with light pulses. Data was taken at several APS beamlines: 7-ID-C, 11-ID-D, 33-BM and 33-ID-C.

“Although this new state of matter, a so called supercrystal, does not exist naturally, it can be created by illuminating carefully engineered thin layers of two distinct materials using light,” said Venkatraman Gopalan, professor of materials science and engineering and physics at Penn State.

“A lot of work went into measuring the motion of a tiny object,” Freeland said. “The question was, how do we see these phenomena with X-rays? We could see that there was something interesting with the system, something we might be able to characterize with ultrafast timescale probes.”

The APS was able to take snapshots of these vortices at nanosecond time scales — a hundred million times faster than it takes to blink your eyes — but the research team discovered this was not fast enough.

“We knew something exciting must be happening that we couldn’t detect,” Wen said. “The APS experiments helped us pinpoint where we want to measure, at faster time scales that we were not able to access at the APS. But LCLS, our sister facility at SLAC, provides the exact tools needed to solve this puzzle.”

With their prior research in hand, Wen and Freeland joined colleagues from SLAC and DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab) — Gopalan and Long-Qing Chen of Pennsylvania State University; Jirka Hlinka, head of the Department of Dielectrics at the Institute of Physics of the Czech Academy of Sciences; Paul Evans of the University of Wisconsin, Madison; and their teams — to design a new experiment that would be able to tell them how these atoms behave, and whether that behavior could be controlled. Using what they learned at APS, the team — including the lead authors of the new paper, Qian Li and Vladimir Stoica, both post-doctoral researchers at the APS at the time of this work — pursued further investigations at the LCLS at SLAC.

“LCLS uses X-ray beams to take snapshots of what atoms are doing at timescales not accessible to conventional X-ray apparatus,” said Aaron Lindenberg, associate professor of materials science and engineering and photon sciences at Stanford University and SLAC. “X-ray scattering can map out structures, but it takes a machine like LCLS to see where the atoms are and to track how they are dynamically moving at unimaginably fast speeds.”

Using a new ferroelectric material designed by Ramamoorthy Ramesh and Lane Martin at Berkeley Lab, the team was able to excite a group of atoms into swirling motion by an electric field at terahertz frequencies, the frequency that’s roughly 1,000 times faster than the processor in your cell phone. They were able to then capture images of those spins at femtosecond timescales. A femtosecond is a quadrillionth of a second — it’s such a short period of time that light can only travel about the length of a small bacteria before it’s over.

With this level of precision, the research team saw a new type of motion they had not seen before.

“Despite theorists having been interested in this type of motion, the exact dynamical properties of polar vortices remained nebulous until the completion of this experiment,” Hlinka said. “The experimental findings helped theorists to refine the model, providing a microscopic insight in the experimental observations. It was a real adventure to reveal this sort of concerted atomic dance.”

This discovery opens up a new set of questions that will take further experiments to answer, and planned upgrades of both the APS and LCLS light sources will help push this research further. LCLS-II, now under construction, will increase its X-ray pulses from 120 to 1 million per second, enabling scientists to look at the dynamics of materials with unprecedented accuracy.

And the APS Upgrade, which will replace the current electron storage ring with a state-of-the-art model that will increase the brightness of the coherent X-rays up to 500 times, will enable researchers to image small objects like these vortices with nanometer resolution.

Researchers can already see the possible applications of this knowledge. The fact that these materials can be tuned by applying small changes opens up a wide range of possibilities, Lindenberg said.

“From a fundamental perspective we are seeing a new type of matter,” he said. “From a technological perspective of information storage, we want to take advantage of what is happening at these frequencies for high-speed, high-bandwidth storage technology. I am excited about controlling the properties of this material, and this experiment shows possible ways of doing this in a dynamical sense, faster than we thought possible.”

Wen and Freeland agreed, noting that these materials may have applications that no one has thought of yet.

“You don’t want something that does what a transistor does, because we have transistors already,” Freeland said. “So you look for new phenomena. What aspects can they bring? We look for objects with faster speed. This is what inspires people. How can we do something different?”

Previous research has suggested that a sexual division of labor existed in Europe during the transition to the Neolithic period, when farming practices spread across the continent. However, many questions remain as to how different tasks became culturally associated with women, men, and perhaps other genders at this time.

To provide further insights, Masclans and colleagues analyzed over 400 stone tools buried in graves in various cemeteries in central Europe about 5,000 years ago during the Early Neolithic. They examined the tools’ physical characteristics, including microscopic patterns of wear, in order to determine how the tools were used. Then, they analyzed these clues in the context of isotopic and osteological data from the graves.

The analysis showed that people of male biological sex were buried with stone tools that had previously been used for woodwork, butchery, hunting, or interpersonal violence. Meanwhile, those of female biological sex were buried with stone tools used on animal hides or leather.

The researchers also found geographic variations in these results, hinting that as agricultural practices spread westwards, sexual division of labor may have shifted. The authors note that the analyzed tools were not necessarily used by the specific people they were buried with, but could have been chosen to represent activities typically carried out by different genders.

These findings provide new support for the existence of sexual division of labor in the early Neolithic in Europe. The authors hope their study will contribute to better understanding of the complex factors involved in the rise of gender inequalities in the Neolithic, which may be heavily rooted in the division of labor during the transition to farming.

The authors add: “Our study points towards a complex and dynamic gendered social organisation rooted in a sexed division of labour from the earliest Neolithic.”

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The absence of such data led to LandCover6k, a project now in its sixth year that includes more than 200 archaeologists, historians, geographers, paleoecologists, and climate modelers around the world.

Led by archeologists Kathleen Morrison of the University of Pennsylvania, Marco Madella of the Universitat Pompeu Fabra, and Nicki Whitehouse of the University of Glasgow, with data expertise from Penn landscape archaeologist Emily Hammer and others, LandCover6k’s goal is to aggregate archaeological and historical evidence of land-use systems from four slices of time — 12,000 years ago, 6,000 years ago, 4,000 years ago, and around the year 1500 — into a single database that anyone can comprehend and use.

The project offers what the researchers hope will become a tool to improve predictions about the planet’s future, plus fill in gaps about its past. “Understanding the human impact on the Earth is more than looking at past vegetation. It’s also important to understand how humans used the land and in particular, the relationship between human land use and vegetation,” Morrison says.

Though current Earth system models suggest that human activity during the past 12,000 years influenced regional and global climate, Madella says, “the models do not capture the diversity and intensity of human activities that affected past land cover, nor do they capture carbon and water cycles.”

Archaeology provides important information around land use that “helps reveal how humans have affected past land cover at a global scale,” adds Whitehouse, “including the crops and animals being farmed, how they were being farmed, and how much land was needed to feed growing populations.”

In a new PLOS ONE paper, the team provides a detailed introduction to LandCover6k’s land-use classification system and global database.

Creating a common language, system

To share such data meant first creating a common language that scientists across disciplines could understand. It’s a task more fraught than it might sound, Morrison says. “Classification means putting hard edges on something. That’s very challenging, as archaeologists are often much more comfortable with narrative.”

Partially because of a lack of shared terminology, archaeologists have not tried to aggregate and compare data on a global scale, something the project’s paleoecologists and modelers had already been doing, she adds. “We spent years consulting with colleagues around the world, discussing all the different types of land use and developing a communication system — the same language, the same terminology — that could be used anywhere.”

Because such categories historically have had different meaning depending on place, context, and time period, some archaeologists initially balked at committing to single definitions for each. Hammer offers the concept of “farming” as an example. “The line between what is called ‘farming’ and what is considered small-scale food production by hunter-gatherers really varies across the world,” she says. So, how could the field fairly judge when the actions of hunter-gatherers managing wild plant and animal resources became “farming”?

Questions like these prompted the LandCover6k team to create a hierarchy within the classification system, with an upper-level category capturing an idea at its broadest and several distinct sub-categories funneling down from there. In the farming example, the research team created a sub-group — low-level food production — which could include the work of the hunter-gatherers. The hope was to offer enough nuance for the archeological community yet still make the data accessible to climate modelers.

In addition to this flexible hierarchy and the uniform terminology, the final classification has three other principal features. It is scale- and source-independent, meaning it accounts for the myriad ways something can be studied. It “takes the perspective of land rather than people,” as the researchers write in PLOS ONE, and it employs a consistent 8×8 kilometer grid scale. “That’s quite large, from an archaeological perspective,” Hammer says, “but we did that so that one person isn’t drawing something very small and another person very large.”

Concrete examples

To showcase how the classification works, the researchers offer the example of the Middle East 6,000 years ago. This region, the area represented by modern day Iraq, Syria, Jordan, Kuwait, Saudi Arabia, Qatar, Bahrain, the United Arab Emirates, Oman, and Yemen, was home to some of the earliest agriculture in the world. Using the new classification and database, project participants built a regional land-use map, despite data availability differing from one spot to the next.

“Mesopotamia has been studied since the mid-19th century so there’s a lot of data and a lot of syntheses to rely on,” Hammer explains. “Arabia has not been nearly as well-studied. There are only a couple of data points, particularly for this period, and because of climatic events, the data are even rarer than for other periods. We wanted to illustrate the approach you would take in a situation where you have a lot of data versus a place with just a little.” The new map of Middle Eastern land is proof of concept for the project, showing the contrast between the settled farms of Mesopotamia and the more sparsely settled lands of Arabia.

The researchers don’t see information gaps, like those of Arabia, as problematic. Rather because the land-use database also records data coverage and quality, it can highlight areas needing more research. “Humans have transformed landscapes for thousands of years,” Morrison says. “But we can’t just say that. We have to demonstrate it.”

And that’s just what LandCover6k aims to do, merging what archaeologists have gleaned about human land use from different times and places into a single, accessible database for climate modelers — and each other. “This project is really about translating what we do,” Hammer says, “not only about the standardization of the terminology so we can talk at a global scale, but also about weaving together the narratives of the past.”

“One of our most important findings is the arrangement of cross-struts within the vertebral centrum,” says Dave Martill of the University of Portsmouth, UK. “It is unlike anything seen previously in a vertebra of any animal. The neural tube is placed centrally within the vertebra and is connected to the external wall via a number of thin rod-like trabeculae, radially arranged like the spokes of a bicycle wheel and helically arranged along the length of the vertebra. They even cross over like the spokes of a bicycle wheel. Evolution shaped these creatures into awesome, breathtakingly efficient flyers.”

Scientists previously thought the pterosaur’s neck had a simpler tube-within-a-tube structure, he explains. But it raised an important question: how could their thin-walled bones, needed to reduce weight in the flying reptiles, still support their bodies and allow them to capture and eat heavy prey animals?

Cariad Williams, the study’s first author, hadn’t set out to answer that question. She wanted to examine the degree of movement between each vertebra of the pterosaur’s neck.

“These animals have ridiculously long necks,” Williams says, adding that, in some species, the fifth vertebra of the neck from the head end is as long as the animal’s body. “It makes a giraffe look perfectly normal. We wanted to know a bit about how this incredibly long neck functioned, as it seems to have very little mobility between each vertebra.”

While the Moroccan pterosaur bones they study are well preserved in three dimensions, the researchers still hadn’t expected the scans to offer such a clear view of the vertebra’s intricate internal structure.

“We did not originally CT scan it to learn about the inside; we wanted a very detailed image of the outside surface,” Martill says. “We could have got this by ordinary surface scanning, but we had an opportunity to put some specimens in a CT scanner, and it seemed churlish to turn the offer down. We were simply trying to model the degree of movement between all the vertebrae to see how the neck might perform in life.”

He adds, “What was utterly remarkable was that the internal structure was perfectly preserved — so too was the microhistology when we made some petrographic sections through the bone. As soon as we saw the intricate pattern of radial trabeculae, we realized there was something special going on. As we looked closer, we could see that they were arranged in a helix traveling up and down the vertebral tube and crossing each other like bicycle wheel spokes.”

His team realized immediately that they needed to bring in engineers to understand how the biomechanics of this unusual neck would have worked. Those analyses suggest that as few as 50 of the spoke-like trabeculae increased the amount of weight their necks could carry without buckling by 90%. Together with the basic tube-within-a-tube structure, it explains how the relatively light-weight animals could capture and carry heavy prey items without breaking their necks.

“It appears that this structure of extremely thin cervical vertebrae and added helically arranged cross-struts resolved many concerns about the biomechanics of how these creatures were able to support massive heads — longer than 1.5 meters — on necks longer than the modern-day giraffe, all whilst retaining the ability of powered flight,” Martill says.

While pterosaurs are sometimes thought of as evolutionary dead ends, Martill and colleagues say the new findings reveal them as “fantastically complex and sophisticated.” Their bones and skeletons were marvels of biology — extremely light yet strong and durable.

The researchers say there’s still much to learn in future work about pterosaurs, including seemingly basic questions about their flight abilities and feeding ecology.

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