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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 nonlinear optical response 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 computational method 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 inversion symmetry deep inside the antiferromagnet was almost untouched.

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:

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.

When analyzing artworks, understanding the visual clarity of compositions is crucial. Inspired by digital artists, Okinawa Institute of Science and Technology (OIST) researchers from the Mechanics and Materials Unit have created a metric to quantify clarity in digital images. As a result, scientists can accurately capture changes in structure during artistic processes and physical transformations.

This new metric can improve analysis and decision-making across the scientific and creative domains, potentially transforming how we understand and evaluate the structure of images. It has been tested on digital artworks and physical systems. The research is published in the journal PNAS.

Researchers have doubled the number of known dark comets, identifying two distinct types: larger ones in the outer solar system and smaller ones in the inner solar system.

This discovery raises new questions about their origins and their role in delivering life-sustaining materials to Earth.

Dark Comet Discoveries

Physicist Christian Schneider has been awarded a prestigious Consolidator Grant from the European Research Council (ERC) for his groundbreaking research into two-dimensional materials and their optical properties. Schneider, a professor at the University of Oldenburg in Germany, will receive approximately two million euros in funding over the next five years to support his “Dual Twist” project.

This research focuses on a novel class of atomically thin materials and their remarkable properties, which hold significant promise for advancing optical technologies.

Together with his team, Schneider will develop experimental set-ups specially designed to study the unique properties of the materials under investigation using light, and pave the way for their application in novel quantum technologies. ERC Consolidator Grants aim to support excellent scientists conducting innovative research in Europe and help them to consolidate their scientific independence. Out of a total of 2,313 applications, the ERC has now selected 328 projects for funding, 67 of which are based in Germany.

Researchers at MIT have developed a design framework for controlling ultrasound wave propagation in microscale acoustic metamaterials, focusing on the precise positioning of microscale spheres within a lattice.

This approach enables tunable wave velocities and responses, and is applicable in fields like ultrasound imaging and mechanical computing.

Acoustic Metamaterials

’The world’s best’ graphene ink, which can be used for printed electronics—such as an intelligent t-shirt that measures your pulse—has been developed in collaboration with the Danish Technological Institute in a MADE demonstration project. The newly developed ink has already opened new markets for the company Danish Graphene.

Imagine a super-strong spider web that can bend and stretch without breaking.

Continue reading “New graphene ink enables the smart wearables of the future” »

Scientists have made a satisfying and intriguing physics discovery some 16 years after it was first predicted to be a possibility: a quasiparticle (a group of particles behaving as one) that only has an effective mass when moving in one direction.

In physics, mass generally refers to a property of particles that relates to things like their energy and resistance to movement. Yet not all mass is built the same – some describes the energy of a particle at rest, for example, while mass may also take into account the energy of a particle’s motion.

In this case, the effective mass describes the quasiparticle’s response to forces, which varies depending on whether the movement through the material is up and down, or back and forth.