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Friction that cools: Threshold effects enable self-stopping robot swarms

How can a horde of active robots be automatically brought to a standstill? By arresting their dynamics in a self-sustained way. This phenomenon was discovered by physicists at Heinrich Heine University Dusseldorf (HHU) and La Sapienza University in Rome. The threshold principle of static friction with the ground plays a decisive role here: it removes the kinetic energy of two robots after a mutual collision so efficiently that they can no longer set themselves in motion.

The researchers describe in the journal Nature Communications that this fundamental effect can also be used to construct controllable moving systems.

Friction creates heat, as anyone knows who has rubbed their hands together in winter weather. And costs energy. Road friction on vehicle tires, for example, will cause a moving car to steadily slow down unless the accelerator is used.

Scientists achieve direct measurement of quantum metric tensor in black phosphorus

Quantum distance refers to a measure of quantum mechanical similarity between two quantum states. A quantum distance of one means that the two quantum states are the same, whereas a quantum distance of zero implies that they are exactly the opposite. Physicists introduced this concept in the realm of theoretical science a long time ago, but its importance has been increasingly recognized in the field of physics only in recent times.

In the last few years, many have tried to measure the quantum distance of electrons in real , but a direct measurement of the quantum distance and thus quantum metric tensor—a key geometric quantity in modern physics defined in terms of the distance between nearby quantum states—has remained elusive so far.

Since the quantum metric tensor is highly relevant in explaining and understanding fundamental physical phenomena in solids, it is, therefore, crucial to come up with an effective methodology for its direct measurement in solid-state systems.

Ultrafast light switch achieved with asymmetric silicon metasurfaces in nanophotonics

In nanophotonics, tiny structures are used to control light at the nanoscale and render it useful for technological applications. A key element here is optical resonators, which trap and amplify light of a certain color (wavelength).

Previous methods of controlling these resonances were more like a dimmer switch: You could weaken the resonance or slightly shift its color. However, genuine on-and-off switching was not possible, as the resonators always remain fundamentally coupled with the light.

A team led by Andreas Tittl, Professor of Experimental Physics at LMU, has now precisely achieved this breakthrough, together with partners from Monash University in Australia. As the researchers report in the journal Nature, they have developed a new method for controlling the coupling between nanoresonators and light in a targeted manner on ultrafast timescales. In this way, a resonance can be created from nothing within a few picoseconds or made to vanish completely again.

Newly derived optical formula shines a light on organic crystal altermagnet candidate

Researchers have uncovered the magnetic properties and underlying mechanisms of a novel magnet using advanced optical techniques. Their study focused on an organic crystal believed to be a promising candidate for an “altermagnet”—a recently proposed third class of magnetic materials. Unlike conventional ferromagnets and antiferromagnets, altermagnets exhibit unique magnetic behavior.

“Unlike typical magnets that attract each other, altermagnets do not exhibit net magnetization, yet they can still influence the polarization of reflected light,” points out Satoshi Iguchi, associate professor at Tohoku University’s Institute for Materials Research. “This makes them difficult to study using conventional optical techniques.”

To overcome this, Iguchi and his colleagues applied a newly derived general formula for light reflection to the organic crystal, successfully clarifying its and origin. The work is published in the journal Physical Review Research.

A dual ion beam tests new steel under fusion energy-producing conditions

A new class of advanced steels needs more fine-tuning before use in system components for fusion energy—a more sustainable alternative to fission that combines two light atoms rather than splitting one heavy atom. The alloy, a type of reduced activation ferritic/martensitic or RAFM steel, contains billions of nanoscale particles of titanium carbide meant to absorb radiation and trap helium produced by fusion within a single component.

When subjected to and concentrations representative of fusion, the titanium-carbide precipitates initially helped trap helium but later dissolved under high damage levels. After dissolving, the alloy swelled as it was no longer able to disperse and trap helium, which could compromise system components.

The first-of-its-kind systematic investigation led by University of Michigan engineers was published in Acta Materialia and the Journal of Nuclear Materials in a series of three papers.

Scientists Were Wrong: Apollo 16 Rocks Rewrite the Story of the Moon’s Exosphere

The Moon’s surface is constantly exposed to the solar wind, a stream of charged particles emitted by the Sun. These energetic ions can dislodge atoms from the Moon’s outermost rocky layer, contributing to the formation of a very sparse layer of gas around the Moon known as the exosphere. However, the exact mechanism behind the creation of this exosphere has remained unclear.

Researchers at TU Wien, working with international collaborators, have now shown that a major contributing process, sputtering caused by the solar wind, has been greatly overestimated in earlier studies. This discrepancy stems from previous models overlooking the Moon’s actual surface texture, which is rough and porous.

For the first time, the team used original Apollo 16 samples in high-precision laboratory experiments, along with advanced 3D modeling, to calculate more accurate sputtering rates. Their findings are published in Communications Earth & Environment.

Cheaper, Stronger Titanium? New 3D-Printing Breakthrough Makes It Possible

Researchers at RMIT University in Australia have developed a new form of titanium for 3D printing that costs approximately 33% less than the titanium alloys currently in widespread use.

Replacing expensive elements

The researchers substituted vanadium, which has become increasingly costly, with more affordable and widely available alternative elements.

Quantum Breakthrough: Scientists Find “Backdoor” to 60-Year-Old Superconducting Mystery

A Copenhagen team has unlocked a clever “backdoor” into studying rare quantum states once thought beyond reach.

Scientists at the Niels Bohr Institute, University of Copenhagen, have discovered a new approach for investigating rare quantum states that occur within superconducting vortices. These states were first proposed in the 1960s, but confirming their existence has proven extremely challenging because they occur at energy levels too small for most experiments to detect directly.

This breakthrough was achieved through a mix of creative problem-solving and the advanced development of custom-made materials in the Niels Bohr Institute’s laboratories. The research findings have been published in Physical Review Letters.

Scientists Discover the Explosive Chain Reaction That Triggers Lightning

Lightning may look like a sudden burst from the clouds, but its true origin lies in an invisible storm of cosmic rays, X-rays, and high-energy electrons. A breakthrough study led by Penn State researchers has finally decoded this hidden process: when cosmic rays strike thunderclouds, they trigger

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