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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.

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.

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.

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.

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.

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.

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.

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.

Continue reading “In a first, MIT researchers successfully trap electrons in 3D crystal” »

For more than 50 years, the semiconductor industry has been hard at work developing advanced technologies that have led to the amazing increases in computing power and energy efficiency that have improved our lives. A primary way the industry has achieved these remarkable performance gains has been by finding ways to decrease the size of the semiconductor devices in microchips. However, with semiconductor feature sizes now approaching only a few nanometers—just a few hundred atoms—it has become increasingly challenging to sustain continued device miniaturization.

To address the challenges associated with fabricating even smaller microchip components, the semiconductor industry is currently transitioning to a more powerful fabrication method—extreme ultraviolet (EUV) lithography. EUV lithography employs light that is only 13.5 nanometers in wavelength to form tiny circuit patterns in a photoresist, the light-sensitive material integral to the lithography process.

The photoresist is the template for forming the nanoscale circuit patterns in the silicon semiconductor. As EUV lithography begins paving the way for the future, scientists are faced with the hurdle of identifying the most effective resist materials for this new era of nanofabrication.

In a new study, researchers from the University of California, Santa Barbara, (UCSB) have reported the discovery of a spin microemulsion in two-dimensional systems of spinor Bose-Einstein condensates, shedding light on a novel phase transition marked by the loss of superfluidity, complex pseudospin textures, and the emergence of topological defects.

A Bose-Einstein (B-E) condensate is a state of matter that occurs at extremely low temperatures, where bosons, such as photons, become indistinguishable and behave as a single quantum entity, forming a superfluid or superconducting state.

B-E condensates can exhibit unique quantum properties, such as a spin microemulsion. When the internal spin states of atoms in a B-E condensate are coupled to their motion, a unique phase called a spin microemulsion can emerge.