Scientists have made the first experimental observation of matter wave diffraction in a short-lived electron-positron atom.
Category: particle physics
Confirming altermagnetism in an abundant mineral
Also known as magnetoelectronics, spintronics rely on electron spin rather than electron charge, as found in traditional electronics. Although spintronics is still an emerging field, spintronic technologies are already found in hard disk drives and giant magnetoresistance sensors used in industrial and automotive applications. Once the right foundational materials are discovered and verified, including economical materials for altermagnets, spintronics could advance technologies from wireless communication to quantum computing.
Researchers using neutrons at the Department of Energy’s Oak Ridge National Laboratory’s Spallation Neutron Source (SNS) discovered that hematite, essentially rust, can help design energy-efficient spintronics.
The team’s findings, published in Physical Review Letters, confirmed a key signature of altermagnetism (a new type of magnetism discovered in 2022) in hematite. Altermagnets are magnetic materials in which electron spins align in opposite directions, allowing pure spin currents to flow without a net electric charge—ideal conditions for spintronics. The team measured spin waves, which move through a material’s magnetic order similar to how sound waves move through air. They discovered that these waves show a clear separation in energy, a unique signature that confirms the material’s altermagnetic nature.
New laser method gives insight into radioactive atomic nuclei
By directing pulses of laser light at atoms, researchers can study how radioactive elements decay in a matter of seconds. The method is described in a new thesis from the University of Gothenburg, which shows that the atomic nuclei of the elements neptunium and fermium are shaped like rugby balls.
Actinides are a group of elements at the bottom of the periodic table. They have a high density, are radioactive, and several of them only exist for a few seconds before they decay. Only four of the 14 elements in this group occur naturally on Earth. The others can be produced in an accelerator, but only in very small quantities. Uranium is the best-known actinide, but a new thesis from the University of Gothenburg focuses on neptunium and fermium.
The Gravity Particle Should Exist. So Where Is It?
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Physics is this close to understanding the entire universe. And what lives in this gap? Many physicists think it’s the elusive graviton—the quantum particle of gravity—whose discovery will finally allow us to stitch together our two great theories of nature into a single master theory. But what is the graviton, and does it even exist?
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Superconductor Theory Under Cold-Atom Scrutiny
Snapshot measurements of cold-atom gases reveal hidden spin correlations that could force an update of some superconductivity theories.
Our understanding of nature is inherently bound to the experimental tools we build to observe the world. Superconductivity, for example, has been traditionally studied using current and voltage meters under a variety of temperatures and other environmental conditions. From these observations, theorists have developed models—notably the Bardeen-Cooper-Schrieffer (BCS) theory, which assumes that the zero-resistance flow in a superconductor arises from electrons forming so-called Cooper pairs. This theory has been successful in explaining a large class of superconductors, but Tarik Yefsah from the Ecole Normale Supérieure in Paris and colleagues have now observed behavior that contradicts BCS predictions [1]. Using a recently developed technique called atom-resolved continuum quantum gas microscopy, the researchers directly observed spatial correlations in cold atoms that mimic superconducting electrons.
Astronomers crack a decades-old mystery, catching gas morphing into planet-building disks around newborn stars
An international team led by Dr. Indrani Das of Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has shown, for the first time, how infalling gas from star-forming cores gradually transitions into planet-forming disks. Their findings, combining numerical simulations with Atacama Large Millimeter/submillimeter Array (ALMA) observations, are published today in The Astrophysical Journal.
Protoplanetary disks form around young stars when dense molecular cloud cores collapse under their own gravity. An outer shroud of gas and dust, known as the envelope, surrounds and feeds both the young star and the forming disk. While it is well understood that planets eventually form within these disks and follow Keplerian orbits, the mechanism that transforms rapid infalling gas motion from the envelope into ordered Keplerian motion within the disk has remained a mystery for decades.
Based on both theoretical and observational evidence, the recent study discovered that there exists a distinct transition zone at the envelope-disk interface of a young star-disk system, which Das named ENDTRANZ (Envelope Disk Transition Zone). The findings have established that infalling gas motions gradually transition into Keplerian motions across this transition zone. Crucially, this transition is far from abrupt and contradicts earlier infall models that are based on classical test-particle dynamics.
Dark matter could explain the earliest supermassive black holes
A growing mystery in astronomy is the presence of gargantuan black holes—some weighing as much as a billion suns—existing less than a billion years after the Big Bang. According to the standard theory of black hole formation, these black holes simply should not have had enough time to grow so large. A study led by University of California, Riverside graduate student Yash Aggarwal shows that dark matter decays could be the key to understanding the origin of these cosmic behemoths. Published in the Journal of Cosmology and Astroparticle Physics, the research shows that the energy released from dark matter decay could alter the chemistry of early galaxies enough to cause some of them to directly collapse into black holes rather than forming stars.
The result is timely, since NASA’s James Webb Space Telescope continues to observe unusually large black holes in the early universe that could have formed by direct collapse. Astronomers had believed this process requires a coincidence of nearby stars shining onto pre-stellar gas and so expected it to be rare.
Aggarwal’s team goes beyond the standard approach by using dark matter—the unknown 85% of the matter in the universe that helps form galaxies. They show that if dark matter decays, it can leak a small amount of its energy into the gas and supercharge the direct collapse rate. Each decaying dark matter particle would only need to inject an amount of energy that is a billion trillionths of the energy of a single AA battery.
Scientists capture superconductivity’s ‘dancing pairs’ for first time, revealing missing pieces in a decades-old theory
For the first time, scientists have directly imaged the quantum process underlying superconductivity, a phenomenon in which paired electrons cause electric current to flow without resistance at sufficiently low temperatures. The results weren’t quite what they expected.
In the study, published April 15 in Physical Review Letters, the scientists directly imaged individual atoms pairing up in a special gas cooled nearly to absolute zero—the unreachable limit to how cold things can get. The type of gas, called a Fermi gas, allows scientists to substitute electrons with atoms and probe the physics of superconductors in a controlled way.
Surprisingly, the scientists found that after pairing up, the atoms moved in a synchronized dance, with their positions dependent on those of other pairs—a phenomenon not predicted by the 70-year-old, Nobel-prize-winning theory of superconductivity.
Multitasking quantum sensors can measure several properties at once
A special class of sensors leverages quantum properties to measure tiny signals at levels that would be impossible using classical sensors alone. Such quantum sensors are currently being used to study the inner workings of cells and the outer depths of our universe.
Particularly promising are solid-state quantum sensors, which can operate at room temperature. Unfortunately, most solid-state quantum sensors today only measure one physical quantity at a time—such as the magnetic field, temperature, or strain in a material. Trying to measure both the magnetic field and temperature of a material at the same time causes their signals to get mixed up and measurements to become unreliable.
Now, MIT researchers have created a way to simultaneously measure multiple physical quantities with a solid-state quantum sensor. They achieved this by exploiting entanglement, where particles become correlated into a single quantum state. In a new paper, the team demonstrated its approach in a commonly used quantum sensor at room temperature, measuring the amplitude, frequency, and phase of a microwave field in a single measurement. They also showed the approach works better than sequentially measuring each property or using traditional sensors.