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A hidden property of light could power future nanomachines

Light does more than illuminate the world—it can also push and twist matter. It was back in the 1870s that James Clerk Maxwell first predicted that light carries momentum and can exert pressure on objects. Nearly a century later, in the 1970s, Arthur Ashkin asked why not use this property of light to hold and push around tiny particles. He developed optical tweezers that use focused laser beams to trap and move nanoscale objects.

While scientists have long known that light can exert small forces, detecting them has been extremely difficult. Objects at this scale are constantly jostled by random thermal motion, making the subtle influence of light hard to measure.

How maze-like magnetic patterns form and evolve in materials

The rapid increase in electric vehicle adoption in recent years has highlighted a crucial issue: the energy conversion efficiency of electric motors. In electric motors, iron loss or magnetic hysteresis loss is a primary source of energy dissipation, arising from the repeated reversal of magnetic fields within the motor core, made of soft magnetic materials. Moreover, electric motors typically operate in high-temperature environments, where thermal effects can lead to partial demagnetization, further complicating energy-loss mechanisms.

The structure of magnetic domains (tiny magnetic regions) of soft magnetic materials strongly influences their magnetic properties, including response to high temperatures and hysteresis loss.

Magnetic domains exhibit a variety of fine structures. In some soft magnetic materials, they form intricate zig-zag patterns known as maze domains. These maze domains show complex and abrupt temperature-dependent behavior that can significantly affect energy loss.

I’ve fired one of America’s most powerful lasers—here’s what a shot day looks like

If you walk across the open yard in front of the Physics, Math and Astronomy building at the University of Texas at Austin, you’ll see a 17-story tower and a huge L-shaped building. What you won’t see is what’s underneath you. Two floors below ground, behind heavy double doors stamped with a logo that most students have never noticed, sits one of the most powerful lasers in the United States.

I was the lead laser scientist on the Texas Petawatt, or TPW as we called it, from 2020 to 2024. Texas Petawatt, which is currently closed due to funding cuts, was a government-funded research center where scientists from across the country applied for time to use specialized equipment. It was part of LaserNetUS, a Department of Energy network of high-power laser labs.

This type of laser takes a tiny pulse of light, stretches it out so it doesn’t blast optics to pieces, and amplifies it until, for a brief instant, it carries more power than the entire U.S. electrical grid. Then it compresses the pulse back to a trillionth of a second to create a star in a vacuum chamber.

How tiny voids could make fusion targets more stable under powerful shockwaves

Picture two materials sandwiched together. The boundary between them may appear flat, but, in reality, it is full of tiny bumps and dents. Suddenly, the materials are hit with a shockwave. If that wave hits a bump in the material interface, it slows down. If it hits a dent, it accelerates forward. This imbalance creates fast, narrow jets of material—called the Richtmyer-Meshkov (RM) instability.

In a recent paper, published in Physical Review Letters, researchers from Lawrence Livermore National Laboratory (LLNL), Imperial College London and their collaborators used AI to optimize and 3D printing to create a target that effectively negates the RM instability.

“Our target reshapes the shockwave, in both space and time, as it travels through the material,” said first author Jergus Strucka, now at the European XFEL. “Instead of a single shock hitting the surface, we introduce voids to break it up into a sequence of smaller pressure pulses that arrive at slightly different times.”

There’s a range of magic angles to study superconductivity in a twisted 2D semiconductor

Last year, tungsten diselenide (WSe2) had its magic moment. Two independent research groups discovered “magic angles” at which two atom-thin layers of the unique semiconductor, when twisted relative to one another into what’s known as a moire pattern, can superconduct electricity. Cory Dean and his colleagues at Columbia documented superconductivity at a 5° twist angle; upstate at Cornell, Jie Shan and Kin Fai Mak’s team saw it at around 3.5°. Until then, graphene was the only other moire material capable of the feat.

Writing again in Nature on April 1, Dean and his colleagues fill in what happens between their observed magic angle and Cornell’s. Though the initial results struck researchers as two potentially distinct types of superconductivity, they are in fact smoothly connected. “Graphene has a magic angle of 1.1°. WSe2 has a magic continuum,” said Columbia physics graduate student Yinjie Guo, lead author of both Columbia Nature papers.

That wide continuum of superconducting twist angles makes WSe2 a more robust platform to explore the phenomenon than graphene, which cannot deviate by more than a tenth of a degree from its magic angle. “That’s a very specific condition you have to get to, and it’s been a real bottleneck,” noted Dean. “Working with WSe2 is extremely reproducible, which makes it much more possible to build new theories about superconductivity.”

Generalized optical meta-spanners empower arbitrary light paths for multitasking optical manipulation

Have you ever wished to drive microscopic matter along an arbitrarily tailored trajectory instead of just a circle? That’s exactly what we set out to achieve.

The field of photonic force manipulation has opened new avenues for controlling the microscopic world with light. Since the invention of optical tweezers in 1986, the non-contact trapping and manipulation of microscopic particles using the momentum and angular momentum of light has become an indispensable tool in biophysics, soft matter science, and micro-nanotechnology—a contribution recognized by the 2018 Nobel Prize in Physics.

Conventional optical tweezers rely on the intensity gradient of a Gaussian beam to generate a three-dimensional restoring potential for stable particle trapping.

Surprising link between metallicity and superconductivity uncovered in twisted trilayer graphene

Superconductivity is a state of matter characterized by an electrical resistance of zero, typically at very low temperatures. Past studies have found that in various materials, this unique state is accompanied by unusual electron arrangements.

In some superconductors, for instance, electrons spontaneously align in a preferred direction, breaking a property known as rotational symmetry. This directional arrangement of electrons is also known as electronic nematicity.

Moreover, some superconductors also exhibit a strange metallicity. This is a phase characterized by unusual changes in a material’s electrical resistance, which cannot be explained by standard physical theories.

Each protein in the epigenome produces a different pattern of gene expression, study finds

A new study finds the proteins responsible for controlling which genes are expressed in a genome do more than simply turn a gene on or off. Essentially, each type of protein that interacts with a gene produces different behaviors—a finding with ramifications for everything from biomedical therapeutics to biological computing. A paper on the study, “Epigenome Regulators Imbue a Single Eukaryotic Promoter with Diverse Gene Expression Dynamics,” is published in the journal iScience.

At issue are “epigenome regulators.” Every organism’s genome is made up of DNA. But that DNA is bound up with many different proteins into very compact structures. The proteins that are bound to the DNA are called the epigenome, and they control which parts of the DNA get expressed. Your blood cells, nerve cells, and skin cells all have the same DNA, but perform very different functions. That’s because different parts of the DNA sequence are being expressed in each cell—and that is largely controlled by which proteins are bound to different parts of the DNA in each cell.

“We already knew that the proteins in the epigenome control the way DNA is expressed,” says Albert Keung, corresponding author of the study and an associate professor of chemical and biomolecular engineering at North Carolina State University. “Our goal here was to look at a single gene and quantify the full range of ways that the gene could be expressed by different proteins.” Keung is the Goodnight Distinguished Scholar in Innovation in Biotechnology and Biomolecular Engineering and director of biotechnology programs in NC State’s Integrative Sciences Initiative.

Six new isolated millisecond pulsars discovered with FAST

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Chinese astronomers have inspected two nearby galactic globular clusters, namely NGC 6517 and NGC 7078. The study resulted in the discovery of six new millisecond pulsars in these clusters, which are isolated and faint. The finding was detailed in a paper published April 9 on the arXiv pre-print server.

The physics of brain development: How cells pull together to form the neural tube

In about one out of every 1,000 pregnancies, the neural tube, a key nervous system structure, fails to close properly. Georgia Tech physicists are now helping explain why this happens, having uncovered the physics that drive neural tube closure in a pregnancy’s earliest stages.

Working with collaborators at University College London (UCL), Georgia Tech researchers used computer models to reveal how, during early development, forces generated by cells physically pull the neural tube closed—like a drawstring. This discovery offers new insight into a critical process that—when disrupted—can result in severe birth defects such as spina bifida.

“Understanding a complex developmental process like neural tube closure requires a highly interdisciplinary approach,” said Shiladitya Banerjee, an associate professor in the School of Physics. “By combining advanced biological imaging with theoretical physics, we were able to uncover the mechanical rules that drive cells to close the tube. My lab builds computational models to uncover the physical rules of living systems. The neural tube is an ideal focus because its formation requires incredible mechanical coordination.”

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