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Category: particle physics – Page 16

MIT Physicists Zapped a Quantum Crystal With Lasers — and Discovered Something Surprising

MIT physicists have uncovered a surprising split in the behavior of electrons inside a quantum material: two nearly identical electronic patterns rebuild themselves in fundamentally different ways.

Electrons inside a solid do not always behave like independent particles. Under the right conditions, enormous numbers of them can reorganize together, producing entirely new states of matter with properties that the original material did not appear to possess.

MIT physicists have now watched that collective reorganization unfold in unusual detail. Their experiments reveal that two electronic phases occupying the same quantum material can form through fundamentally different mechanisms, even though both involve the same underlying type of electron order.

X-rays: Beyond the Nobel Prize limit

When certain atoms are irradiated with laser light, they can produce a very different kind of laser light: laser pulses with extremely high frequencies in the X-ray range. These laser pulses, which helped achieve record-breaking results at TU Wien in the 1990s, were the subject of the 2023 Nobel Prize in Physics.

However, the theoretical model of this effect makes a clear prediction: There is an upper limit to the energy, depending on the properties of the laser beam directed at the atoms. Above a certain value, known as the energy cutoff, hardly any X-rays are produced.

Now, however, a new experiment jointly performed by teams at TU Wien and the University of California San Diego has succeeded in overcoming this textbook cutoff rule: Using helium atoms, the researchers reached a much higher energy range than standard theory would allow. The reason lies in the interaction between the two electrons in the helium atom: They can release their energy simultaneously.

New CERN measurement challenges conventional models of how gluons behave inside atomic nuclei

A University of Kansas physicist played a leading role in a CERN study showing that two rival explanations for how gluons behave inside atomic nuclei can now be experimentally distinguished.

The research, carried out within the ALICE experiment at CERN’s Large Hadron Collider and published in Physical Review Letters, reports the first multidimensional measurement of incoherent J/ψ (pronounced “JAY-sigh”) photonuclear production as a function of both interaction energy and momentum transfer. The measurement gives scientists their clearest view yet of how gluons, the particles that bind quarks together, are arranged inside atomic nuclei at high energies.

“Although quarks are often described as the fundamental building blocks of matter, nearly all the mass of the visible universe—from the atoms in our bodies to the matter inside stars—actually comes from the energy carried by gluons and the strong force that binds quarks together,” said nuclear physicist Daniel Tapia Takaki, professor of physics & astronomy at KU and member of the ALICE collaboration. “Understanding how gluons behave inside nuclei is therefore essential to understanding how matter itself acquires its mass and structure.”

‘Flying focus’ laser overcomes key limitation in plasma-based particle accelerators

In a new Nature Physics study, researchers accelerated electrons to more than twice the energy predicted by the traditional dephasing limit for laser-plasma accelerators operating over the same distance. This was made possible by a specially engineered laser pulse called a flying focus, which counteracts a longstanding limitation known as “dephasing.”

Laser-plasma accelerators use an intense, ultrashort laser pulse to drive a wave of charge through a plasma. In principle, this makes it possible to accelerate particles to very high energies over just centimeters, rather than kilometers.

The problem is that the accelerating plasma wave cannot keep pace with the electrons riding it. The electrons move at speeds close to the speed of light, but the laser pulse driving the wave travels slightly slower. Over distance, the electrons manage to outrun the plasma wave. This dephasing causes the electrons to stop gaining energy, thereby affecting the amount of energy such accelerators can deliver.

Real-time measurements reveal antiferromagnetic skyrmions move in line with an applied current

Skyrmions—essentially magnetic vortices—represent a promising approach in spintronics; in the future, they could serve as components in storage media or computers, potentially complementing established CMOS technologies. Researchers at Johannes Gutenberg University Mainz (JGU) have now visualized the interaction of antiferromagnetic skyrmions for the first time and shown that antiferromagnetic skyrmions move reproducibly along straight trajectories aligned with the driving electric current.

“Our results establish a quantitative framework for the interactions of antiferromagnetic skyrmions. In doing so, they pave the way for spintronic devices based on large numbers of skyrmions,” said Mona Bhukta from the research group of professor Mathias Kläui at the JGU Institute of Physics. The researchers published their findings today in the journal Nature Physics.

Tiny particles defy action-reaction symmetry to stay in motion

From schools of fish and flocks of birds to microscopic synthetic particles, many systems in nature and the laboratory consist of individual units or agents that move by consuming energy. These systems are known as active matter because their components continuously use energy to generate motion, either individually or through interactions with their environment.

Inspired by such systems, researchers have become increasingly interested in nonreciprocal interactions, in which the influence one particle exerts on another is not equally returned. In other words, one particle can affect another more strongly than it is affected in return, effectively breaking action-reaction symmetry. This is surprising because, under Newton’s third law, passive particles cannot continuously push one another in the same direction.

In this system, however, nonequilibrium electrohydrodynamic flows allow one particle to effectively “chase” another, so activity emerges even though the particles themselves are not self-propelled. Such asymmetry can generate entirely new forms of collective motion and self-organization. However, experimental realizations have largely been limited to small particle clusters.

This AI Can Find the Missing Atoms That X-Rays Cannot See

An AI model adapted from image inpainting can reconstruct missing atoms in crystal structures with a reported 97 percent success rate.

A crystal structure can appear nearly complete yet still be unusable for computer simulations because some of its atoms are missing. Hydrogen is a frequent source of these gaps, and researchers have now adapted an artificial intelligence technique used to repair images to predict where those hidden atoms belong.

The approach was developed by a team led by Giovanni Pizzi of the PSI Center for Scientific Computing, Theory and Data, working with researchers from the universities of Parma and Modena in Italy. Described in npj Computational Materials, the method applies computer vision, in which AI recognizes and interprets visual information, to incomplete crystal structures.

Starlink Satellites Reveal a Hidden Atmosphere 300 Miles Above Earth

Satellites designed to provide internet service are now serving an unexpected second purpose: helping scientists map the nearly invisible atmosphere at the edge of space.

Researchers at Kyoto University have used orbital changes from about 1,200 Starlink satellites to map Earth’s thermosphere, a thin and difficult-to-observe region of the upper atmosphere. Their analysis produced the first tomographic map of its kind, revealing atmospheric density patterns roughly 482 kilometers (300 miles) above Earth. The study was published in Earth, Planets, and Space.

Although satellites in low Earth orbit travel through what appears to be empty space, traces of atmosphere remain even hundreds of kilometers above the surface. Collisions with these sparse particles create drag, slowly reducing a spacecraft’s speed and altitude.

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