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Category: materials – Page 19

Brown dwarfs are curious celestial bodies that appear to straddle the mass divide between stars and planets. Often referred to as “failed stars,” brown dwarfs form in isolation from a collapsing cloud of gas and dust like a star.

However, while fully-fledged stars continue to gather material from the gas and dust cloud that births them, brown dwarfs are less successful at this mass harvesting. As a result, they don’t reach the masses of the smallest stars and can’t trigger the process that defines main sequence stars, like our sun.

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Colloidal gels are complex systems made up of microscopic particles dispersed in a liquid, ultimately producing a semi-solid network. These materials have unique and advantageous properties that can be tuned using external forces, which have been the focus of various physics studies.

Researchers at University of Copenhagen in Denmark and the UGC-DAE Consortium for Scientific Research in India recently ran simulations and performed analyses aimed at understanding how the injection of active particles, such as swimming bacteria, would influence colloidal gels.

Their paper, published in Physical Review Letters, shows that active particles can influence the structure of 3D colloidal gels, kneading them into porous and denser structures.

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In 2011 physicists made a surprising observation: A cuprate material exposed to intense pulses of light appeared to superconduct fleetingly at a temperature above its critical temperature. Could this be a clue to finding higher-temperature superconductors? The answer remains unclear. “There are still continuing debates about whether the light-induced state is really superconducting,” says Morihiko Nishida from the University of Tokyo. Now he and his colleagues have provided new hints concerning the nature of the light-induced state and its connection to electronic wave patterns called charge-density waves (CDWs) [1].

The researchers studied two cuprates, called LNSCO and LSCO, that both contain the element lanthanum. These materials superconduct at temperatures below 10 K, but at slightly higher temperatures, they transition to one of several low-conductivity states in which a wave pattern is imprinted onto the electron distribution. Previous work by this group suggested that these CDWs play a role in light-induced superconductivity [2], but it was unclear whether the wavelength—short or long—of the CDWs had any effect.

In their new experiments, Nishida and colleagues fired near-infrared pulses at their cuprate samples and recorded the electron response with a terahertz probe beam. In the CDW region of parameter space, they observed a light-induced conducting state whose frequency matched that of a superconducting resonance effect. The implication that the light-induced state is superconducting needs to be confirmed with other experiments, but the team’s work has revealed that both short-and long-wavelength CDWs play a role. The results have a bearing on models that suggest that the pairing of electrons—a key feature of superconductivity—occurs in CDW states at temperatures above the normal onset of superconductivity (see Synopsis: Picking out Waves in a Material’s Charge Distribution).

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Crafting a unique and promising research hypothesis is a fundamental skill for any scientist. It can also be time consuming: New PhD candidates might spend the first year of their program trying to decide exactly what to explore in their experiments. What if artificial intelligence could help?

MIT researchers have created a way to autonomously generate and evaluate promising research hypotheses across fields, through human-AI collaboration. In a new paper, they describe how they used this framework to create evidence-driven hypotheses that align with unmet research needs in the field of biologically inspired materials.

Published Wednesday in Advanced Materials, the study was co-authored by Alireza Ghafarollahi, a postdoc in the Laboratory for Atomistic and Molecular Mechanics (LAMM), and Markus Buehler, the Jerry McAfee Professor in Engineering in MIT’s departments of Civil and Environmental Engineering and of Mechanical Engineering and director of LAMM.

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For the first time, scientists have imaged an entirely new form of magnetism called altermagnetism.

The researchers used cutting-edge x-ray techniques to visualize and fine-tune this novel magnetic material, which is very different from the kind of magnets we know in day-to-day life.

Their findings, published in Nature, demonstrate that altermagnetic materials can be precisely controlled in microscopic devices, marking a major step forward in magnetic and material science.

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Mechanical crystals, also known as phononic crystals, are materials that can control the propagation of vibrations or sound waves, just like photonic crystals control the flow of light. The introduction of defects in these crystals (i.e., intentional disruptions in their periodic structure) can give rise to mechanical modes within the band gap, enabling the confinement of mechanical waves to smaller regions or the materials—a feature that could be leveraged to create new technologies.

Researchers at McGill University recently realized a new mechanical crystal with an optically programmable defect mode. Their paper, published in Physical Review Letters, introduces a new approach to dynamically reprogram mechanical systems, which entails the use of an optical spring to transfer a mechanical mode into a crystal’s band gap.

“Some time ago, our group was thinking a lot about using an optical spring to partially levitate structures and improve their performance,” Jack C. Sankey, principal investigator and co-author of the paper, told Phys.org. “At the same time, we were watching the amazing breakthroughs in our field with mechanical devices that used the band gap of a phononic crystal to insulate mechanical systems from the noisy environment.”

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A team of researchers has identified a unique phenomenon, a “skin effect,” in the nonlinear optical responses of antiferromagnetic materials. The research, published in Physical Review Letters, provides new insights into the properties of these materials and their potential applications in advanced technologies.

Nonlinear optical effects occur when light interacts with materials that lack inversion symmetry. It was previously thought that these effects were uniformly distributed throughout the material. However, the research team discovered that in antiferromagnets, the can be concentrated on the surfaces, similar to the “skin effect” seen in conductors, where currents flow primarily on the surface.

In this study, the team developed a self-designed to investigate the nonlinear optical responses in antiferromagnets, using the bulk photovoltaic effect as a representative example. Their results showed that, while the global inversion symmetry was broken, the local deep inside the antiferromagnet was almost untouched.

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Using dual lasers and an advanced gas injection system, researchers at the Berkeley Lab Laser Accelerator Center (BELLA) accelerated a high-quality electron beam to 10 billion electronvolts (10 GeV) over a distance of just 30 centimeters.

Laser-plasma accelerators have the potential to dramatically shrink the size and cost of particle accelerators, benefiting fields such as high-energy physics, medicine, and materials science. Key achievements from BELLA’s recent experiment include:

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A recent study has revealed that nearly half of black holes that consume stars during tidal disruption events (TDEs) later emit remnants of those stars, sometimes years after the initial event. TDEs occur when a star ventures too close to a black hole, where the black hole’s gravitational pull exerts intense tidal forces. This results in the star being stretched and compressed, a process known as spaghettification, which tears the star apart within hours. This destruction is marked by a burst of electromagnetic radiation visible as a bright flash.

As the star is consumed, part of its material is expelled, while the remaining material forms an accretion disk—a thin, rotating structure around the black hole. The accretion disk initially releases material in chaotic bursts, detectable through radio waves, but these emissions typically fade within a few months. Traditionally, astronomers only observed these radio emissions for a short period after the star’s destruction, missing any longer-term activity.

The new study, led by Yvette Cendes, a research associate at the Harvard and Smithsonian Center for Astrophysics, involved monitoring black holes for several years after TDEs. Published on Aug. 25 in the preprint database arXiv, the findings showed that in up to 50% of the cases, black holes expelled material years after consuming a star. In 10 of the 24 studied black holes, this delayed emission occurred between two and six years after the initial star-destroying event. These unexpected “burps” were observed as sudden bursts of radio waves, indicating that the black holes “turned on” again long after the initial event.

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