Icy Hot Plasmas: Fluffy, Electrically Charged Ice Grains Reveal New Plasma Dynamics

Ice grains, illuminated by a green sheet of laser light, are suspended in the plasma discharge (purple). Insets show individual ice grains imaged with 20x magnification.
Image Credit: Bellan Plasma Group/Caltech

When a gas is highly energized, its electrons get torn from the parent atoms, resulting in a plasma—the oft-forgotten fourth state of matter (along with solid, liquid, and gas). When we think of plasmas, we normally think of extremely hot phenomena such as the Sun, lightning, or maybe arc welding, but there are situations in which icy cold particles are associated with plasmas. Images of distant molecular clouds from the James Webb Space Telescope feature such hot–cold interactions, with frozen dust illuminated by pockets of shocked gas and newborn stars.

Now a team of Caltech researchers has managed to recreate such an icy plasma system in the lab. They created a plasma in which electrons and positively charged ions exist between ultracold electrodes within a mostly neutral gas environment, injected water vapor, and then watched as tiny ice grains spontaneously formed. They studied the behavior of the grains using a camera with a long-distance microscope lens. The team was surprised to find that extremely "fluffy" grains developed under these conditions and grew into fractal shapes—branching, irregular structures that are self-similar at various scales. And that structure leads to some unexpected physics.

A new approach links quantum physics and gravitation

Quantum-Geodesics 
Large masses – such as a galaxy – curve space-time. Objects move along a geodesic. If we take into account that space-time itself has quantum properties, deviations arise (dashed line vs. solid line).
Image Credit: © TU Wien  

A team at TU Wien combines quantum physics and general relativity theory – and discovers striking deviations from previous results. 

It is something like the “Holy Grail” of physics: unifying particle physics and gravitation. The world of tiny particles is described extremely well by quantum theory, while the world of gravitation is captured by Einstein’s general theory of relativity. But combining the two has not yet worked – the two leading theories of theoretical physics still do not quite fit together. 

There are many ideas for such a unification – with names like string theory, loop quantum gravity, canonical quantum gravity or asymptotically safe gravity. Each of them has its strengths and weaknesses. What has been missing so far, however, are observable predictions for measurable quantities and experimental data that could reveal which of these theories describes nature best. A new study from TU Wien may now have brought us a small step closer to this ambitious goal. 

Untangling magnetism

Spin-wave spectrum of CoFe₂O₄ measured on the MAPS spectrometer (left) and the corresponding spin-wave calculation (right). The large ~60 meV splitting between the two magnon branches originates from the strong imbalance of molecular fields on the A and B cation sites, as illustrated in the inset crystal structure.
Image Credit: KyotoU / Yusuke Nambu

Magnetostriction and spin dynamics are fundamental properties of magnetic materials.  Despite having been studied for decades, finding a decisive link between the two in bulk single crystals had remained elusive. That is until a research team from several institutions, including Kyoto University, sought to examine these properties in the compound CoFe2O4, a spinel oxide (chemical formula AB2O4) widely used in numerous medical and industrial applications.

Spin dynamics describe how the tiny magnetic moments of atoms in a magnetic material interact and change orientation with time, while magnetostriction describes how a material changes shape or dimensions in response to a change in magnetization. These properties are central to the operation of sensors and actuators that employ magnetoelastic materials that change their magnetization under mechanical stress.

When Quantum Gases Refuse to Follow the Rules

The team  Frederik Møller, Philipp Schüttelkopf and Jörg Schmiedmayer
Photo Credit: © Technische Universität Wien

At TU Wien, researchers have created a one-dimensional “quantum wire” made from a gas of ultracold atoms, where mass and energy flow without friction or loss. 

In physical systems, transport takes many forms, such as electric current through a wire, heat through metal, or even water through a pipe. Each of these flows can be described by how easily the underlying quantity—charge, energy, or mass—moves through a material. Normally, collisions and friction lead to resistance causing these flows to slow down or fade away. But in a new experiment at TU Wien, scientists have observed a system where that doesn’t happen at all. 

By confining thousands of rubidium atoms to move along a single line using magnetic and optical fields, they created an ultracold quantum gas in which energy and mass move with perfect efficiency. The results, now published in the journal Science, show that even after countless collisions, the flow remains stable and undiminished, thus revealing a kind of transport that defies the rules of ordinary matter. 

Consciousness as the foundation – new theory of the nature of reality

Maria Strømme, Professor of Materials Science.
Inset Photo Credit: Courtesy of Uppsala University

Consciousness is fundamental; only thereafter do time, space and matter arise. This is the starting point for a new theoretical model of the nature of reality, presented by Maria Strømme, Professor of Materials Science at Uppsala University, in the scientific journal AIP Advances. The article has been selected as the best paper of the issue and featured on the cover. 

Strømme, who normally conducts research in nanotechnology, here takes a major leap from the smallest scales to the very largest – and proposes an entirely new theory of the origin of the universe. The article presents a framework in which consciousness is not viewed as a byproduct of brain activity, but as a fundamental field underlying everything we experience – matter, space, time, and life itself. 

Particle accelerator waste could help produce cancer-fighting materials

Photo Credit: Courtesy of University of York

Energy that would normally go to waste inside powerful particle accelerators could be used to create valuable medical isotopes, scientists have found. 

The next step is to explore how the method could be scaled up to deliver clinically use 

Researchers at the University of York have shown that intense radiation captured in particle accelerator “beam dumps” could be repurposed to produce materials used in cancer therapy.  

Scientists have now found a way to make those leftover photons do a second job, without affecting the main physics experiments. 

A beam of photons designed to investigate things like the matter that makes up our universe, could at the same time, be used to create useful medical isotopes in the diagnosis and treatment of cancer. 

Light causes atomic layers to do the twist

Fang Liu, assistant professor of chemistry in Stanford’s School of Humanities and Sciences
Photo Credit: Fawn Hallenbeck/Stanford University

A study led by Stanford and Cornell researchers shows how light could be used to control the behavior of moiré materials, atomically thin layers that gain unusual properties when stacked and offset. The research has implications for developing superconductivity, magnetism, and quantum electronics.

A pulse of light sets the tempo in the material. Atoms in a crystalline sheet just a few atoms thick begin to move—not randomly, but in a coordinated rhythm, twisting and untwisting in sync like dancers following a beat.

Until now, researchers hadn’t been able to directly observe how those layers physically respond to a burst of light. In a recent study, a team led by Stanford and Cornell University researchers showed that the atomic layers can briefly twist more tightly together, then spring back, like a coiled ribbon releasing its energy.

Rare Particle Pairs Point to Primordial Soup's Temperature at Different Stages

The STAR detector, which is as large as a house, specializes in tracking the thousands of particles produced by each ion collision at the Relativistic Heavy Ion Collider.
Photo Credit: Kevin Coughlin/Brookhaven National Laboratory

At the Relativistic Heavy Ion Collider (RHIC), a U.S. Department of Energy (DOE) Office of Science user facility for nuclear physics research at DOE’s Brookhaven National Laboratory, scientists recreate the ultra-hot conditions of the early universe by smashing particles together at nearly the speed of light. RHIC's collisions delve into mysteries about the properties of matter by melting the colliding particles into a quark-gluon plasma (QGP) — a soup of fundamental particles that are the building blocks of protons and neutrons.

A new analysis of data captured by the STAR detector at RHIC revealed the QGP’s temperature at different stages of its evolution following collisions of gold ions — the nuclei of gold atoms stripped of their electrons. These measurements are key to mapping out how nuclear matter changes as quarks and gluons in the hot soup cool and coalesce to form more ordinary nuclear particles. Studying this phase transition at RHIC is helping physicists understand what happened in the briefest moments at the beginning of the universe, the last time the QGP existed in nature.

Physicists observe key evidence of unconventional superconductivity in magic-angle graphene

MIT researchers observed clear signatures of unconventional superconductivity in magic-angle twisted trilayer graphene (MATTG). The image illustrates pairs of superconducting electrons (yellow spheres) traveling through MATTG, as the team’s new method (represented by magnifying glass) probes the material’s unconventional superconducting gap (represented by the V-shaped beam).
Image Credit: Sampson Wilcox and Emily Theobald, MIT RLE

Superconductors are like the express trains in a metro system. Any electricity that “boards” a superconducting material can zip through it without stopping and losing energy along the way. As such, superconductors are extremely energy efficient, and are used today to power a variety of applications, from MRI machines to particle accelerators.

But these “conventional” superconductors are somewhat limited in terms of uses because they must be brought down to ultra-low temperatures using elaborate cooling systems to keep them in their superconducting state. If superconductors could work at higher, room-like temperatures, they would enable a new world of technologies, from zero-energy-loss power cables and electricity grids to practical quantum computing systems. And so scientists at MIT and elsewhere are studying “unconventional” superconductors — materials that exhibit superconductivity in ways that are different from, and potentially more promising than, today’s superconductors.

In a promising breakthrough, MIT physicists have today reported their observation of new key evidence of unconventional superconductivity in “magic-angle” twisted tri-layer graphene (MATTG) — a material that is made by stacking three atomically-thin sheets of graphene at a specific angle, or twist, that then allows exotic properties to emerge.

Physicists discover new state of matter in electrons, platform to study quantum phenomena

From left, researchers Cyprian Lewandowski, Aman Kumar and Hitesh Changlani.
Photo Credit: Devin Bittner/FSU College of Arts and Sciences

Electricity powers our lives, including our cars, phones, computers and more, through the movement of electrons within a circuit. While we can’t see these electrons, electric currents moving through a conductor flow like water through a pipe to produce electricity.

Certain materials, however, allow that electron flow to “freeze” into crystallized shapes, triggering a transition in the state of matter that the electrons collectively form. This turns the material from a conductor to an insulator, stopping the flow of electrons and providing a unique window into their complex behavior. This phenomenon makes possible new technologies in quantum computing, advanced superconductivity for energy and medical imaging, lighting, and highly precise atomic clocks. 

A team of Florida State University-based physicists, including National High Magnetic Field Laboratory Dirac Postdoctoral Fellow Aman Kumar, Associate Professor Hitesh Changlani and Assistant Professor Cyprian Lewandowski, have shown the conditions necessary to stabilize a phase of matter in which electrons exist in a solid crystalline lattice but can “melt” into a liquid state, known as a generalized Wigner crystal. Their work was published in npj Quantum Materials, a Nature publication. 

The Saltwater Formula

Mannum Waterfalls in South Australia
Photo Credit: © denisbin Creative Commons 2.0  

A solution to a tricky groundwater riddle from Australia: Researchers at TU Wien have developed numerical models to simulate the movement of fluids in porous materials.

Things are complicated along the Murray–Darling River in southern Australia. Agricultural irrigation washes salt out of the upper soil layers, and this salt eventually ends up in the river. To prevent the river’s salt concentration from rising too much, part of the salty water is diverted into special basins. Some of these basins are designed to let the salty water evaporate, others to slowly release it in a controlled manner in the underground. That keeps salt temporarily out of the river and allows a better management of the river’s water—but increases the salinity in the ground. How can we calculate how this saltwater spreads underground and what its long-term effects will be?

Such questions are extremely difficult to answer, as several physical effects interact in complex ways. At TU Wien, researchers have now developed an efficient computer model that can run on supercomputers to calculate the spreading of fluids in porous materials—allowing the movement of saltwater in the soils, like in the case of the Murray–Darling River, to be predicted much more accurately. The same approach can also be applied to other problems, such as the dispersion of pollutants in groundwater.

Birch leaves and peanuts turned into advanced laser technology

Upper: The biomaterial-based random laser when activated. Lower: The same laser seen in daylight.
 Photo Credit: Zhihao Huang

Physicists at Umeå University, in collaboration with researchers in China, have developed a laser made entirely from biomaterials – birch leaves and peanut kernels. The environmentally friendly laser could become an inexpensive and accessible tool for medical diagnostics and imaging.

The results have been published in the scientific journal Nanophotonics and show how a so-called random laser can be made entirely from biological materials.

“Our study shows that it is possible to create advanced optical technology in a simple way using only local, renewable materials,” says Jia Wang, Associate Professor at the Department of Physics, Umeå University, and one of the authors of the study.

A random laser is a type of laser in which light scatters many times inside a disordered material before emerging as a focused beam. It holds great promise for applications such as medical imaging and early disease detection, and has therefore attracted significant research attention. However, conventional random laser materials are often toxic or expensive and complex to produce.

The crystal that makes clouds rain

The experiments have to be performed in the dark
Photo Credit: Technische Universität Wien

No one can control the weather, but certain clouds can be deliberately triggered to release rain or snow. The process, known as cloud seeding, typically involves dispersing small silver iodide particles from aircraft into clouds. These particles act as seeds on which water molecules accumulate, forming ice crystals that grow and eventually become heavy enough to fall to the ground as rain or snow.

Until now, the microscopic details of this process have remained unclear. Using high-resolution microscopy and computer simulations, researchers at TU Wien have investigated how silver iodide interacts with water at the atomic scale. Their findings reveal that silver iodide exposes two fundamentally different surfaces, but only one of them promotes ice nucleation. The discovery deepens our understanding of how clouds form rain and snow and may guide the design of improved materials for inducing precipitation.

How constant is the fine structure constant?

The thorium crystal 
The core element of the experiment: a crystal containing thorium atoms.
Photo Credit: Technische Universität Wien

Thorium atomic nuclei can be used for very specific precision measurements. This had been suspected for decades, and the search for suitable atomic nucleus states had been ongoing worldwide. In 2024, a team from TU Wien, with the support of international partners, achieved the decisive breakthrough: the long-discussed thorium nuclear transition was found. Shortly afterwards, it was demonstrated that thorium can indeed be used to build high-precision nuclear clocks.

Now the next major success in high-precision research on thorium nuclei has been achieved: when the thorium nucleus changes between different states, it slightly alters its elliptical shape. This also changes the distribution of protons in the nucleus, which in turn alters its electric field. This can be measured so precisely that it allows for better investigation than ever before of the fine structure constant, one of the most important natural constants in physics. This now makes it possible to investigate the question of how constant the fundamental constants of nature really are.

Neutrinos ‘flavor’ may hold clues to the universe’s biggest secrets

Inside the Super-Kamiokande detector.
Photo Credit: Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo.

In a new analysis, physicists provide the most precise picture yet of how neutrinos change ‘flavor’ as they travel through the cosmos. 

Neutrinos are fundamental particles of the universe, but also some of the most elusive; They pass through everything and can be extremely difficult to detect. While many of their properties are mysterious, scientists know neutrinos come in three types: electron, muon, and tau. 

Understanding these different identities can help scientists learn more about neutrino masses and answer key questions about the evolution of the universe, including why matter came to dominate over antimatter in the early universe, said Zoya Vallari, 

Exotic roto-crystals

Spontaneous fragmentation of a rotating crystal comprised of transversely interacting particles into multiple rotating crystal fragments.
Image Credit: Wayne State University/Zhi-Feng Huang

It sounds bizarre, but they exist: crystals made of rotating objects. Physicists from Aachen, Düsseldorf, Mainz and Wayne State (Detroit, USA) have jointly studied these exotic objects and their properties. They easily break into individual fragments, have odd grain boundaries and evidence defects that can be controlled in a targeted fashion. In an article published in the Proceedings of the National Academy of Sciences, the researchers outline how several new properties of such “transverse interaction” systems can be predicted by applying a comprehensive theory.

“Transverse forces” can occur in synthetic systems, such as in certain magnetic solids. They exist in systems of living organisms too, however. In an experiment observing a host of starfish embryos conducted at American university MIT, it was found that, through their swimming movements, the embryos influence each other in a manner leading them to rotate around one another. What biological function this may have is not yet understood. The common thread in these systems is that they involve rotating objects.

The key to why the universe exists may lie in an 1800s knot idea science once dismissed

The model suggests a brief “knot-dominated era,” when these tangled energy fields outweighed everything else, a scenario that could be probed through gravitational-wave signals.
Image Credit: Courtesy of Muneto Nitta/Hiroshima University

In 1867, Lord Kelvin imagined atoms as knots in the aether. The idea was soon disproven. Atoms turned out to be something else entirely. But his discarded vision may yet hold the key to why the universe exists.

Now, for the first time, Japanese physicists have shown that knots can arise in a realistic particle physics framework, one that also tackles deep puzzles such as neutrino masses, dark matter, and the strong CP problem. Their findings, in Physical Review Letters, suggest these “cosmic knots” could have formed and briefly dominated in the turbulent newborn universe, collapsing in ways that favored matter over antimatter and leaving behind a unique hum in spacetime that future detectors could listen for—a rarity for a physics mystery that’s notoriously hard to probe.

“This study addresses one of the most fundamental mysteries in physics: why our Universe is made of matter and not antimatter,” said study corresponding author Muneto Nitta, professor (special appointment) at Hiroshima University’s International Institute for Sustainability with Knotted Chiral Meta Matter (WPI-SKCM2) in Japan.

“This question is important because it touches directly on why stars, galaxies, and we ourselves exist at all.”

The Quantum Door Mystery: Electrons That Can’t Find the Exit

Photo Credit: © Technische Universität Wien

What happens when electrons leave a solid material? This seemingly simple phenomenon has eluded accurate theoretical description until now. Researchers have found the missing piece of the puzzle.

Imagine a frog sitting inside a box. The box has a large opening at a certain height. Can the frog escape? That depends on how much energy it has: if it can jump high enough, it could in principle make it out. But whether it actually succeeds is another question. The height of the jump alone isn’t enough — the frog also needs to jump through the opening.

A similar situation arises with electrons inside a solid. When given a bit of extra energy — for example, by bombarding the material with additional electrons — they may be able to escape from the material. This effect has been known for many years and is widely used in technology. But surprisingly, it has never been possible to calculate this process accurately. A collaboration between several research groups at TU Wien has now solved this mystery: just like the frog, it’s not only the energy that matters — the electron also needs to find the right “exit,” a so-called “doorway state.”

Physicists probe quark‑gluon plasma temperatures, helping paint more detailed picture of big bang

Frank Geurts is a professor of physics and astronomy at Rice and co-spokesperson of the RHIC STAR collaboration.
Photo Credit: Jeff Fitlow/Rice University.

A research team led by Rice University physicist Frank Geurts has successfully measured the temperature of quark-gluon plasma (QGP) at various stages of its evolution, providing critical insights into a state of matter believed to have existed just microseconds after the big bang, a scientific theory describing the origin and evolution of the universe. 

The study addresses the long-standing challenge of measuring the temperature of matter under extreme conditions where direct access is impossible. By using thermal electron-positron pairs emitted during ultrarelativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York, the researchers have decoded the thermal profile of QGP. 

Temperature measurements existed previously but have been plagued by several complications such as whether they were of the QGP phase or biased by a Doppler-like effect from the large velocity fields pushing such effective temperatures.

“Our measurements unlock QGP’s thermal fingerprint,” said Geurts, a professor of physics and astronomy and co-spokesperson of the RHIC STAR collaboration. “Tracking dilepton emissions has allowed us to determine how hot the plasma was and when it started to cool, providing a direct view of conditions just microseconds after the universe’s inception.” 

Metamaterials can stifle vibrations with intentional complexity

This 3-D printed “kagome tube” can passively isolate vibrations using its complex, but deliberate, structure.
Image Credit: James McInerney, Air Force Research Laboratory

In science and engineering, it’s unusual for innovation to come in one fell swoop. It’s more often a painstaking plod through which the extraordinary gradually becomes ordinary.

But we may be at an inflection point along that path when it comes to engineered structures whose mechanical properties are unlike anything seen before in nature, also known as mechanical metamaterials. A team led by researchers at the University of Michigan and the Air Force Research Laboratory, or AFRL, have shown how to 3D print intricate tubes that can use their complex structure to stymy vibrations.

Such structures could be useful in a variety of applications where people want to dampen vibrations, including transportation, civil engineering and more. The team’s new study, published in the journal Physical Review Applied, builds on decades of theoretical and computational research to create structures that passively impede vibrations trying to move from one end to the other.