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The Unexpected Ubiquity of the Phonon Thermal Hall Effect

The discovery of a thermal version of the Hall effect in common semiconductors challenges our understanding of how magnetic fields and heat fluxes interact within solids.

In the late 19th century, two physicists independently discovered the Righi-Leduc, or thermal Hall, effect: In the presence of a perpendicular magnetic field, a longitudinal heat flux generates a transverse temperature gradient. In metals, the thermal Hall effect is tied to the more familiar electric Hall effect through the Wiedemann-Franz law, which states that electronic thermal conductivity divided by electrical conductivity is directly proportional to temperature.

In electrical insulators, lattice vibrations called phonons carry heat. Until the early 21st century, it was thought that phonons, despite being neutral, could still generate a nonzero thermal Hall signal, provided they are scattered by electron spins. However, since then many experiments worldwide have found that such a signal can be detected even in crystalline insulators with no unpaired electron spins. The decisive discovery was made last year by Xiaobo Jin of Fudan University in China and his colleagues, who found a phonon thermal Hall effect in two simple semiconducting materials: silicon and germanium [1]. Whereas the origin of the effect is hotly debated, its importance in challenging views of how magnetic fields and heat fluxes interact is undisputed.

Bending nanoribbons tunes diamond’s light emission without doping

In a new Physical Review Letters study, researchers have demonstrated that bending diamond nanostructures can tune the light they emit without doping.

Diamond is an ultrawide bandgap semiconductor with high carrier mobility, high thermal conductivity, deep-ultraviolet light emission and stable single-photon emission. These properties make it a potential candidate for next-generation electronic and optoelectronic devices.

However, properties such as its bandgap and light emission are difficult to tune because doping in diamond poses limitations. Elastic strain engineering, which stretches or compresses a material without permanently deforming it, has emerged as an alternative.

Laser-made muons produce first images of dense objects

Muons are constantly being created as cosmic rays collide with molecules in Earth’s upper atmosphere. With their ability to penetrate far into dense, solid materials, these cosmic muons are often used to image the insides of objects that are otherwise hidden from view. However, the flow of these natural particles is far too slow for the technique to become both fast and reliable in practical settings.

Through new research posted to the preprint server arXiv, a team including Madalina Dobre at the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering in Romania has created images using an artificial muon beam for the first time.

After 20 years, jet diffusion wakes detected in quark-gluon plasmas

Boats passing over smooth water form a pair of diffusion wakes behind them veering off at a certain angle. Turbulence occurs along the line directly behind the boat, but the two diffusion waves are at a theoretical angle of 19.5° from the same line, for deep, ideally smooth water.

Now physicists have for the first time measured diffusion wakes of jets passing through quark-gluon plasmas (QGP), a phenomenon first predicted 20 years ago after it was realized that QGPs are liquid not a plasma (that is, like a gas). In fact, they are the most perfect liquid in the universe. The result, obtained by the CMS Collaboration, is published in Physical Review Letters.

QGPs were the state of the universe for its first few microseconds, from about a trillionth of a second after the Big Bang to a few microseconds after. It is 200,000 times hotter than the center of the sun, and its viscosity was first inferred in 2005 in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York.

New magnetic computing system could tackle complex optimization problems

When designing new computer chips, engineers need to make various decisions about how to connect their underlying components while efficiently using limited space. Planning these connections involves combinatorial optimization, or, in other words, a search for the best combination of choices under specific rules.

Ising machines, computing systems inspired by a mathematical model describing interacting magnets, could be promising for solving combinatorial optimization tasks. These systems represent choices using spins, which in this context are variables that can have one of two values. By changing these values, Ising machines can search for the best combination of options for solving specific problems.

Researchers at Beihang University, Suzhou Inston Technology Co. Ltd. and Empyrean Technology Co. Ltd. recently developed a new Ising machine based on spintronics, technologies that use the magnetic properties of materials to process or store information. The new machine, introduced in a paper published in Nature Electronics, could solve complex combinatorial optimization tasks, including planning wiring routes and assigning connections to different wiring layers in computer chips.

3D light fields push electrons into quantum states previously beyond experimental reach

Using the same method, they were also able to excite electrons into quantum states that had previously been inaccessible in experiments.

This approach opens up new experimental avenues for identifying chiral structures, controlling interactions between light and matter and generating specific electronic quantum states, the researchers report in the journal Physical Review Research.

Zinc oxide quantum dots enable faster charge detection, laying groundwork for spin qubits

Researchers at Tohoku University, in collaboration with the National Institute for Materials Science (NIMS) and the University of Tokyo, have taken an important step toward semiconductor quantum computing using zinc oxide (ZnO).

The team successfully demonstrated charge sensing, high-frequency reflectometry and the formation of a few-electron double quantum dot in a ZnO device—three key technologies for developing and evaluating spin qubits.

The work is published in the journal Physical Review Applied.

Physicists identify ‘octupolar’ magnetism, with implications for quantum technologies

Most magnets have two poles: north and south, or positive and negative, in a familiar arrangement called a “dipole.” But researchers are increasingly uncovering more complex forms of magnetism.

Recent advances in quantum mechanics have revealed higher orders of magnetism, including an “octupolar order” in which a pattern of particles arranged in a crystalline structure within a material behaves as if it has eight magnetic poles rather than the familiar two. However, detecting and controlling these elusive magnetic states is a significant challenge.

Now, a team led by quantum physicists at the University of Toronto has established a new method for observing quantum magnetic states using light to probe the atomic vibrations produced as electrons spin. The work is a critical first step toward harnessing multipolar magnetism for practical technologies, including next-generation data storage and computing devices.

Researchers Uncover a Hidden Molecular Machine Parasites Need To Survive

Researchers have visualized two key stages of RNA processing in parasites that cause diseases such as sleeping sickness, Chagas’ disease, and leishmaniasis.

For nearly 40 years, scientists have known that trypanosomatid parasites depend on an unusual system for processing RNA. Now researchers have captured that machinery at near-atomic resolution, showing how its components assemble and operate during a reaction the parasites need to survive.

The study, conducted by researchers at the University of Liège and Rockefeller University, reconstructed the three-dimensional architecture of the trans-spliceosome, a massive molecular machine that prepares genetic messages for use inside trypanosomatid cells. The structures also identify features that differ from the RNA processing machinery found in humans, providing a potential starting point for developing drugs that interfere selectively with the parasites.

When Your Eyes Mislead You, the Brain Finds Common Ground

A mouse study suggests that neighboring visual areas may build agreement by sustaining shared activity patterns while mismatches fade.

A shape in the dark might briefly resemble a face, or an orange might momentarily look like an apple. To make sense of what we see, the brain must coordinate information from regions with different specialties. A study in mice now suggests how two neighboring visual areas may reach a consistent interpretation, with shared activity persisting while mismatches quickly fade.

The research, published in Nature Neuroscience, examined the primary visual cortex, known as V1, and the lateromedial visual area, or LM. Both belong to the visual cortex, the part of the brain that processes sight. When activity patterns in the two areas agreed, they lasted longer. When the patterns disagreed, the mismatch dissipated within a fraction of a second.

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