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Category: particle physics – Page 228

Laser pulse compression by a density gradient plasma for exawatt to zettawatt lasers

A new method of creating laser pulses, more than 1,000 times as powerful as those currently in existence, has been proposed by scientists in the UK and South Korea.

The scientists have used in joint research to demonstrate a new way of compressing light to increase its intensity sufficiently to extract particles from vacuum and study the nature of matter. To achieve this the three groups have come together to produce a very special type of mirror—one that not only reflects pulses of light but compresses them in time by a factor of more than two hundred times, with further compression possible.

The groups from the University of Strathclyde, UNIST and GIST propose a simple idea—to use the gradient in the density of plasma, which is fully ionized matter, to cause photons to “bunch,” analogous to the way a stretched-out group of cars bunch up as they encounter a steep hill. This could revolutionize the next generation of lasers to enable their powers to increase by more than one million times from what is achievable now.

Tracking down quantum fluctuations of the vacuum to explore the limits of physics

Absolutely empty—that is how most of us envision the vacuum. Yet, in reality, it is filled with an energetic flickering: the quantum fluctuations.

Experts are currently preparing a laser experiment intended to verify these vacuum fluctuations in a novel way, which could potentially provide clues to new laws in physics. A research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has developed a series of proposals designed to help conduct the experiment more effectively—thus increasing the chances of success. The team presents its findings in Physical Review D.

The physics world has long been aware that the vacuum is not entirely void but is filled with vacuum fluctuations—an ominous quantum flickering in time and space. Although it cannot be captured directly, its influence can be indirectly observed, for example, through changes in the electromagnetic fields of tiny particles.

Direct Writing of a Titania Foam in Microgravity for Photocatalytic Applications

This work explores the potential for additive manufacturing to be used to fabricate ultraviolet light-blocking or photocatalytic materials with in situ resource utilization, using a titania foam as a model system. Direct foam writing was used to deposit titania-based foam lines in microgravity using parabolic flight. The wet foam was based on titania primary particles and a titania precursor (Ti (IV) bis(ammonium lactato) dihydroxide). Lines were also printed in Earth gravity and their resulting properties were compared with regard to average cross-sectional area, height, and width. The cross-sectional height was found to be higher when printing at low speeds in microgravity compared to Earth gravity, but lower when printing at high speeds in microgravity compared to Earth gravity. It was also observed that volumetric flow rate was generally higher when writing in Earth gravity compared to microgravity. Additionally, heterogeneous photocatalytic degradation of methylene blue was studied to characterize the foams for water purification and was found to generally increase as the foam heat treatment temperature increased. Optical and scanning electron microscopies were used to observe foam morphology. X-ray diffraction spectroscopy was used to study the change in crystallinity with respect to temperature. Contact angle of water was found to increase on the surface of the foam as ultraviolet light exposure time increased. Additionally, the foam blocked more ultraviolet light over time when exposed to ultraviolet radiation. Finally, bubble coarsening measurements were taken to observe bubble radius growth over time.

Synchronized Surfing of Self-Propelled Particles

Millimeter-sized “surfers” can self-propel across a vibrating liquid surface, interacting with other surfers to create collective patterns.

Self-propelled objects can move in mesmerizing patterns. The collective movements of groups of such objects typically occur in one of two flow regimes: the inertial regime—think swirling schools of fish in water—or the viscous regime—think swarming colonies of bacteria in mucus. Some self-propelled objects can travel in both flow regimes, a possibility that is less explored. Daniel Harris at Brown University, Rhode Island, and colleagues have studied the motion of a new system of self-propelled objects that move in this intermediate regime, finding that the objects organize into several distinct and tunable motion patterns [1]. The researchers say that their surfers may serve as a versatile, accessible model system for developing a detailed understanding of active matter in the intermediate flow regime.

The team considered millimeter-scale plastic “surfers” floating atop a vertically vibrated pool containing a mixture of water and glycerol. The surfers resembled miniature, rectangular boats and had uneven weight distributions across their lengths. With heavier sterns than bows, the surfers bobbed up and down like seesaws when the liquid surface vibrated. The waves that then emanated from the bow and stern of each surfer had unequal amplitudes, with the sterns creating waves with higher amplitudes.

A twist on atomic sheets to create new materials

The way light interacts with naturally occurring materials is well-understood in physics and materials science. But in recent decades, researchers have fabricated metamaterials that interact with light in new ways that go beyond the physical limits imposed on naturally occurring materials.

A metamaterial is composed of arrays of “meta-atoms,” which have been fabricated into desirable structures on the scale of about a hundred nanometers. The structure of arrays of meta-atoms facilitate precise light-matter interactions. However, the large size of meta-atoms relative to regular atoms, which are smaller than a nanometer, has limited the performance of metamaterials for practical applications.

Now, a collaborative research team led by Bo Zhen of the University of Pennsylvania has unveiled a new approach that directly engineers atomic structures of material by stacking the two-dimensional arrays in spiral formations to tap into novel light-matter interaction. This approach enables metamaterials to overcome the current technical limitations and paves the way for next-generation lasers, imaging, and quantum technologies. Their findings were published in the journal Nature Photonics.

High-harmonic probes to unravel the secrets of spin

More sophisticated manipulation of complicated materials and their spin states at short time scales will be needed to create the next generation of spintronic devices. But, a thorough understanding of the fundamental physics underpinning nanoscale spin manipulation is necessary to fully utilize these powers for more energy-efficient nanotechnologies.

The JILA team and colleagues from institutions in Sweden, Greece, and Germany investigated the spin dynamics within a unique substance known as a Heusler compound—a combination of metals that exhibits properties similar to those of a single magnetic material. In their investigation, the scientists used a cobalt, manganese, and gallium combination that acted as an insulator for electrons with downwardly oriented spins and a conductor for those with upwardly aligned spins.

Scientists used extreme ultraviolet high-harmonic generation (EUV HHG) light as a probe to track the re-orientations of the spins inside the compound after exciting it with a femtosecond laser. Tuning the color of the EUV HHG probe light is the key to accurately interpreting the spin re-orientations.

Quantum Wonders: Atomic Dance Transforms Crystal Into a Magnet

Researchers at Rice University found that chiral phonons in a crystal can magnetize the material, aligning electron spins in a way similar to the effect of a strong magnetic field. This discovery challenges established notions in physics, particularly the concept of time-reversal symmetry, and paves the way for advanced research in quantum materials.

Quantum materials hold the key to a future of lightning-speed, energy-efficient information systems. The problem with tapping their transformative potential is that, in solids, the vast number of atoms often drowns out the exotic quantum properties electrons carry.

Rice University researchers in the lab of quantum materials scientist Hanyu Zhu found that when they move in circles, atoms can also work wonders: When the atomic lattice in a rare-earth crystal becomes animated with a corkscrew-shaped vibration known as a chiral phonon, the crystal is transformed into a magnet.

Probing the intricate structures of 2D materials at the nanoscale

Two-dimensional (2D) materials, composed of a single or a few layers of atoms, are at the forefront of material science, promising revolutionary advancements in technology. These ultra-thin materials exhibit unique and exotic properties, particularly when their layers are stacked and twisted in specific ways.

This manipulation of layers can significantly alter their electronic characteristics, presenting exciting opportunities for the development of next-generation technologies such as more efficient computers and reliable electricity storage systems.

Understanding the intricate relationship between the atomic structure and electronic properties of these materials, however, poses a significant challenge. Traditional microscopy techniques struggle to capture the complete 3D atomic structure of these layered materials, especially when the layers are oriented differently or composed of light elements.

Study leverages chiral phonons for transformative quantum effect

Quantum materials hold the key to a future of lightning-speed, energy-efficient information systems. The problem with tapping their transformative potential is that in solids, the vast number of atoms often drowns out the exotic quantum properties electrons carry.

Rice University researchers in the lab of quantum materials scientist Hanyu Zhu found that when they move in circles, atoms can also work wonders: When the in a rare-earth crystal becomes animated with a corkscrew-shaped vibration known as a chiral phonon, the crystal is transformed into a magnet.

According to a new study published in Science, exposing cerium fluoride to ultrafast pulses of light sends its atoms into a dance that momentarily enlists the spins of electrons, causing them to align with the atomic rotation. This alignment would otherwise require a powerful magnetic field to activate, since cerium fluoride is naturally paramagnetic with randomly oriented spins even at zero temperature.

In a first, MIT researchers successfully trap electrons in 3D crystal

Previous attempts at trapping them in 2D had failed.

Successful electron trapping in 3D

The MIT team looked for materials that could be used to work out 3D lattices in kagome patterns and came across pyrochlore — a mineral with highly symmetric atomic arrangements. In 3D, pyrochlore’s atoms formed a repeating pattern consisting of cubes in a kagome-like lattice.

To test their hypothesis, the team synthesized the pyrochlore using calcium and nickel. After heating the ingredients to very high temperatures, the mix was cooled, and the atoms arranged themselves into a kagome-like structure.