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A Lab Version of Planetary Atmospheres
Researchers recreate key features of atmospheric turbulence in a meter-sized rotating cylinder.
Atmospheric turbulence encompasses a wide range of flow patterns, from 10-m-wide eddies to 1000-km-long wind streams. Geoscientists want to understand how energy and rotational motion transfer (or “cascade”) from one length scale to another, but atmospheric observations have not provided clear answers. A new model of the atmosphere consisting of fluid in a rotating, meter-wide cylinder is able to reproduce key features of observed turbulence [1]. Using video tracking, researchers mapped out the flow velocity in this system, uncovering the dominant role of a “vorticity” transfer that distributes rotational motion from large vortices into smaller ones. This form of cascade may explain the energy distribution in large-scale turbulence on Earth as well as on other planets.
Turbulence can be characterized by a kinetic energy spectrum, which indicates the amount of energy found in fluctuations at each length scale. The typical turbulence spectrum has a mathematical form called a power law, in which the energy density steadily decreases from large to small scales. Fluid dynamics models of Earth’s atmosphere have predicted that the power law should be relatively flat at large scales (with an exponent of −5÷3) and steeper at small scales (with an exponent of −3). However, these predictions aren’t supported by observations. “The basic shape of the spectrum is all wrong,” says Peter Read from the University of Oxford in the UK. Data taken by airplanes have revealed a spectrum that starts out steep at large scales (greater than 500 km) and becomes flatter at small scales.
Corralling Interfering Anyons
Link.aps.org/doi/10.1103/Physics.19.
A delicate interference experiment elucidates the collective behavior of quasiparticles that are neither bosons nor fermions, but something in between.
When you live in theory-land, as I do, anyons in fractional quantum Hall (FQH) systems are an emblem of elegance. They address a fundamental question in quantum mechanics—the classification of indistinguishable particles—by breaking the long-rooted dichotomy between fermions and bosons and replacing it with a continuum of possibilities. Their implications are far reaching. Anyons account for the “hierarchy” of FQH states and they inspire visions of topologically protected quantum computation [1]. In experiment-land, the most direct manifestation of anyons is the phase that the system’s wave function acquires when two anyons are interchanged or when one winds around another. This phase is at the heart of a new experiment performed by Noah Samuelson and Andrea Young of the University of California, Santa Barbara, and their collaborators [2].
Compact terahertz imaging system brings real-time, non-invasive clinical diagnostics closer
Scientists at the University of Warwick and University of Exeter have developed a fully fiber-coupled terahertz (THz) imaging system that significantly improves the speed, resolution, and clinical practicality of terahertz imaging. The study, published in Nature Communications, demonstrates a high-throughput, compact platform that overcomes key barriers limiting current THz systems—bringing real-time, non-invasive tissue imaging closer to routine clinical use.
“Terahertz imaging has shown immense promise for biomedical diagnostics, but its translation into real-world clinical tools has been hindered by bulky systems and slow acquisition speeds,” said Professor Emma MacPherson, Department of Physics, University of Warwick. “It’s an exciting breakthrough as the fiber coupling means that the system can be flexible and compact, meaning it can function as a handheld device or be integrated with a robot.”
Terahertz waves sit between microwaves and infrared light on the electromagnetic spectrum. Crucially, they are non-ionizing (meaning they do not carry the risks associated with X-rays) and are highly sensitive to water content, which helps reveal differences between healthy and diseased tissue. Despite this promise, most existing terahertz imaging systems are bulky and slow, limiting their use outside specialist labs.
Electric current stabilizes spins at unstable points for new types of computing
A research team has discovered a new way to control tiny magnetic properties inside materials using electric current, which could possibly pave the way for new types of computing technologies. The work is based on spintronics, a field that uses not only the electric charge of electrons but also their “spin,” a quantum property that can be thought of as a tiny magnet.
Spintronics is already used in magnetic random access memory (MRAM), a type of memory that keeps data even when the power is turned off. This is different from conventional memory, which loses information without electricity.
In MRAM, data is stored depending on whether spins point “up” or “down.” These two stable states are separated by an energy barrier, which helps keep the data secure. However, this stability also makes it harder to switch between states, requiring strong electric currents.
First quantum oscillations observed in gallium nitride holes
Gallium nitride, a semiconductor that can operate at high voltages, temperatures, and frequencies, has enabled technologies from LED lighting to high-power electronics. Now Cornell researchers have observed a quantum property of the material for the first time, an advance that could expand its technological reach.
Much of gallium nitride’s value as a semiconductor lies in how quickly negatively charged electrons move through the material. But the material could become even more useful if scientists better understood its positively charged “holes,” which behave like mobile pockets of missing electrons but have been difficult to study.
Understanding how to control the flow of the holes—as engineers have achieved in silicon semiconductors—would allow gallium nitride to reach its full potential.
A Hall ‘rectenna’ can detect signals over a 100 GHz frequency range
Many current wireless communication, imaging and sensing technologies rely on components that convert oscillating electric and magnetic fields (i.e., electromagnetic waves) into electrical signals. Some of the most used components are so-called p-n diodes, semiconducting devices that combine two types of materials with distinct electrical properties.
In conventional diode designs, the conversion of electromagnetic waves into electrical signals relies on the nonlinear transport of electrons. This means that the electric current in the devices does not change proportionally with the voltage applied, which allows them to rectify signals (i.e., convert alternating current into direct current) and combine signals with different frequencies.
A key limitation of traditional diodes is that thermal effects introduce noise, causing electrons to move randomly and making weak signals harder to detect. Moreover, electrons typically take a finite time to travel across the device, also known as the transit time, which limits the performance of the diodes at very high frequencies.
Superconducting altermagnets could carry spin without energy loss
Researchers have proposed that a newly identified class of magnetic materials could extend the zero-resistance currents of superconductors to electron spins. Publishing their calculations in Physical Review X, Kyle Monkman and colleagues at the University of British Columbia propose how “altermagnets” could enable persistent spin currents to flow without dissipation. If confirmed experimentally, the effect could provide a powerful new platform for spintronics, where information is encoded in spin rather than electric charge.
The ability to transport spins over long distances is a central challenge in spintronics. In conventional metals and semiconductors, spin currents decay rapidly due to effects that randomize electron spins. One promising workaround has been superconducting spintronics, where dissipationless charge transport is combined with magnetic materials. However, these hybrid systems often suffer from intrinsic drawbacks, including stray magnetic fields that can interfere with nearby components, suppressing superconductivity.
First confirmed in 2024, altermagnets offer a potential way around these problems. Like antiferromagnets (where a magnetic dipole’s spin is always opposite to those of its neighbors), they have zero net magnetization, avoiding unwanted magnetic fields.
Physicists find electronic agents that govern flat band quantum materials
Physicists have directly visualized the fundamental electronic building blocks of flat-band quantum materials, a class of systems in which electron motion is effectively quenched and strong interactions give rise to emergent phases of matter. In a study published in Nature Physics, Qimiao Si’s group at Rice University, in collaboration with researchers at the Weizmann Institute of Science, identified compact molecular orbitals that act as the key electronic agents governing the exotic behavior of these materials.
“In flat band materials, electron motion experiences destructive interference,” said Si, the Harry C. and Olga K. Wiess Professor of Physics and Astronomy and director of Rice’s Extreme Quantum Materials Alliance.
These flat band materials are also topological with properties that are preserved as the material continuously bends or stretches in any symmetry-preserving way.
ALICE sees new sign of primordial plasma in proton collisions
The ALICE Collaboration takes a step further in addressing the question of whether a quark–gluon plasma can be formed in proton–proton and proton–nucleus collisions. In the first few microseconds after the Big Bang, the universe was in an extremely hot and dense state of matter known as quark–gluon plasma (QGP), which can be reproduced with high-energy collisions between heavy ions such as lead nuclei.
In a paper published in Nature Communications, the ALICE Collaboration reports observing a remarkable common pattern in proton–proton, proton–lead and lead–lead collisions at the Large Hadron Collider (LHC), shedding new light on possible QGP formation and evolution in small collision systems.
Physicists initially believed that colliding small systems, such as protons, could not generate the extreme temperatures and pressures needed to form QGP. But in recent years, signatures of QGP have been observed in proton–proton and proton–lead collisions at the LHC, indicating that the size of the collision system may not be a limiting factor in QGP creation.