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Category: materials

No Free Lunch for Sound Waves

Sound wave scattering can be increased in one frequency range only by reducing scattering in another range, according to experiments—a discovery relevant for acoustic engineering.

Acoustic metamaterials allow blocking, absorbing, or redirecting waves in ways not possible with conventional materials. Now researchers have shown that all such structures face a previously unrecognized constraint: The total acoustic scattering is fixed, so that boosting scattering in one frequency band necessarily depletes it elsewhere [1]. This general restriction provides a new way of thinking about how acoustic performance can be optimized, which could guide the design of broadband sound-control devices, from noise barriers to acoustic cloaks.

By building structures into materials on length scales smaller than the wavelength of sound, researchers can create artificial resonant elements that interact strongly with acoustic waves. Such structures can produce effects that are difficult or impossible to achieve otherwise—for example, strong sound attenuation through thin material layers. Such advances have led to new techniques for lightweight soundproofing and sound steering.

Physicists discover attractive forces between molecular condensates may cause running off

Inside cells, certain functions are carried out by locally adjusting molecular composition. This condensation of material results in the formation of dense droplets that can dynamically rearrange. Because of this, interactions between such dense regions determine the shaping of condensates. Scientists from the Department of Living Matter Physics at MPI-DS recently developed a model that can describe such phase separation dynamics based solely on attraction. The work is published in the journal Physical Review Letters.

“It’s natural to think that a system with only attractive forces would form one large, stationary condensate,” explained Jacopo Romano, first author of the study.

“However, instead we observed an unexpected emergent property of chasing dynamics resulting in movement and propulsion,” he said.

Ultrathin nanotubes reach 1 nanometer, opening path to smaller electronics

Researchers in Japan have created some of the world’s smallest semiconducting nanotubes, structures 100,000 times thinner than a human hair. By growing molybdenum disulfide inside protective tubes of boron nitride, the researchers, including those from the University of Tokyo, produced highly uniform tubes just 1 nanometer wide, a scale at which it’s difficult to make stable nanotube structures. The work confirms decades-old theoretical predictions about how these ultrafine materials behave and could also provide a new route toward miniaturized electronic devices.

The research is published in the journal Science.

A few years ago, carbon nanotubes were attracting a lot of press attention. But there’s a new contender in the ring, and it offers some advantages over its carbon counterpart that could tempt engineers to design products around it.

How ‘asymmetric alloying’ is creating the next generation of luminescent materials

Metal cluster molecules are discrete compounds containing multiple metal atoms held together by metal–metal and metal–ligand bonding. They serve as excellent candidates for catalysts, biosensors, and even for drug development. Developing atomic-level molecular editing methods for such metal clusters remains an important challenge and represents a promising strategy for expanding their structural and functional diversity. Such approaches can enable structure-specific properties, high near-infrared (NIR) photoluminescence quantum yields, and unique reactivities and electronic structures.

Alloying is a powerful method for achieving this goal. In this regard, a key challenge is asymmetric alloying, which introduces asymmetry into the metal cluster by selectively placing heterometal atoms at nonequivalent sites, desymmetrizing the cluster and therefore imparting chirality-associated functionality.

Moreover, highly selective asymmetric synthesis methods for heterometallic clusters are expected to contribute significantly to the development of chiroptical materials. However, methods capable of achieving such controlled asymmetric synthesis have rarely been reported.

Photoexcitation flips 2D moiré devices from metals to insulators in ultrafast test

Quantum materials, materials with properties that are governed by the laws of quantum mechanics describing many-body interactions, have proved promising for the development of various advanced technologies. Many of these materials undergo so-called phase transitions, switching between different physical states that alter how electrons flow through them.

Some previous studies have demonstrated the transition from insulating states to metallic states in quantum materials, via a process called photoexcitation (i.e., the excitation of electrons using light). Yet the opposite transition, from metallic to insulating states, has so far proved difficult to realize using light alone.

Researchers at Columbia University, in collaboration with UC Riverside, recently demonstrated an ultrafast photo-induced metal-to-insulator transition in two-dimensional (2D) moiré heterostructures, quantum materials consisting of 2D layers stacked on top of each other, with a slight misalignment between them.

New solar desalination breakthrough makes fresh water without toxic brine

Scientists have developed a solar desalination system that turns seawater into drinking water without creating environmentally damaging brine. Special laser-textured metal panels use sunlight to evaporate water while automatically moving salt deposits away from the working surface, preventing clogging. The process was successfully tested with water from three oceans and can recover nearly all salts as solids. Those leftover materials could even become a source of valuable lithium for batteries.

Dormant black hole revives in under three years, brightening 10-fold in nearby galaxy

Astronomers monitoring a nearby active galaxy for six years have watched its supermassive black hole dramatically wake up, brightening by a factor of 10 across ultraviolet and X-ray wavelengths. The paper outlining the study was posted to the preprint server arXiv on May 18.

In active galactic nuclei (AGN), material spiraling into the central black hole releases enormous amounts of energy. The accretion disk—a swirling ring of hot gas—radiates this energy primarily in optical and ultraviolet (UV) light. Additionally, a separate region of extremely hot plasma sits above the disk. It is called the corona, which is responsible for the X-ray emission.

Understanding how these two components relate to each other and how they evolve as a black hole’s feeding rate changes remains an open problem.

When Vera Rubin measured the spin of galaxies

Beginning with the Andromeda galaxy in the late 1960s, the astronomer Vera Rubin and her colleague Kent Ford measured how fast stars and gas clouds orbit at different distances from a galaxy’s centre. They expected the outer material to move slowly. It did not. In Andromeda, and then in galaxy after galaxy, the orbital speed stayed high all the way to the edge of what they could measure. The visible stars, gas and dust could not supply enough gravity to hold matter moving that fast in place.

Rubin and Ford published their Andromeda result in 1970, in a paper in the Astrophysical Journal. Over the following decade they extended the work, and by 1980 had measured the same pattern across twenty-one spiral galaxies. The consistency was the point. One odd galaxy could be explained away. Twenty-one could not.

Topological states emerge in quantum Hall-superconductor devices with multiple channels

Topological phases are unusual states of matter that give rise to properties protected by a material’s overall structure (i.e., “topology”), as opposed to microscopic details. These phases are of great interest for the development of quantum technologies, as they can yield desirable electronic properties that are robust against defects and disturbances.

Researchers at Autonomous University of Madrid investigated the topological phases that emerge in hybrid devices that combine the quantum Hall effect and superconductivity.

The quantum Hall effect is an effect that emerges when the electrical resistance of a two-dimensional (2D) material placed under a strong magnetic field and cooled to temperatures close to absolute zero changes in precise, rigid “steps” rather than continuously. Superconductivity, on the other hand, is a state exhibited by some materials that entails an electrical resistance of zero, typically below a specific critical temperature and magnetic field.

Webb reveals black hole that formed before its galaxy

Which comes first, the galaxy or the black hole? We don’t know, but scientists have long thought it could be the galaxy: Large stars within an existing galaxy consume their fuel and collapse to form black holes, which can gobble up surrounding material and merge over time to form more massive entities.

But it’s hard to figure out how black holes millions to billions of times the mass of the sun, thousands of which have now been detected in the early universe, could have grown so quickly from such small seeds.

Now, researchers using NASA’s James Webb Space Telescope have detected clear evidence that some supermassive black holes were enormous from the beginning, forming without a stellar collapse phase, and without a significantly more massive host galaxy to feed them.

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