Skip to main content

Reset your password

Please enter the e-mail address you used to register to reset your password

Note: The verification e-mail to change your password should arrive immediately. However, in some cases it takes longer. Don't forget to check your spam folder.

If you haven't received the e-mail in 24 hours, please contact customerservices@ioppublishing.org

Registration complete

Thank you for registering with Physics World
If you'd like to change your details at any time, please visit My account

Close
Home » Page 54

How IOP Publishing cut its carbon footprint by 36% since 2020

My guest in this episode of the Physics World Weekly podcast is Liz Martin, who is sustainability lead at IOP Publishing. We chat about how the scholarly publisher has reduced its carbon emissions by 36% when compared to a 2020 baseline – and the challenges and opportunities for achieving further reductions.

Martin talks about the importance of cooperation and partnerships – both internal and external – to achieving environmental goals. This includes engaging with both suppliers and employees on how to reduce carbon emissions.

IOP Publishing is a wholly owned subsidiary of the Institute of Physics, which is the professional body and learned society for physics in the UK and Ireland. It produces over 100 scholarly journals, around half of which are published jointly with or on behalf of partner societies and research organizations. Physics World is also brought to you by IOP Publishing.

  • You can download a PDF of IOP Publishing’s Sustainability Report 2025 here.

Many-body effects at the world’s largest physics conference

Many-body physics is the study of large ensembles of interacting particles and their collective behaviour. These systems are notoriously difficult to simulate, yet they underpin phenomena such as superconductivity and superfluidity. Thus, they are of great interest to understand. As a many-body physicist myself, I arrived at my first American Physical Society (APS) meeting with a different curiosity: understanding what the largest physics conference in the world was all about.

Last week, I joined a crowd of 14,000 scientists convening in Denver, Colorado for the annual Global Physics Summit, hosted by the APS.

On Sunday morning, the day before the conference, I walked alone through the streets of downtown Denver. Silence filled the frigid air. A light flurry of snow covered the empty streets in white. It seemed that the city was still asleep.

But Denver was abruptly awakened on Monday morning, as I found myself well-accompanied by the crowd collectively moving towards the Colorado Convention Center for an 8 a.m. start. Inside, the conference was humming with its own emergent dynamics, with lines forming around coffee stations and people bustling to find their way to wherever they were going.

Throughout the day, I was faced with the repeated indecision of choosing between over 80 simultaneous sessions. Some sessions housed APS’s infamous blitz talks with speakers racing to pack as many graphs and equations into their allotted 10 min. Having barely enough time to write down the takeaways, I tried, often in vain, to fill my memory as quickly as possible.

Other sessions featured longer talks on hot topics in physics. By evening, my mind was swimming with notions of scalable quantum computing and physics funding issues and public engagement opportunities and the infiltration of AI slop into every corner of the scientific process. These sessions offered me a necessary reminder that science is not performed in a vacuum. With that said, the purely technical sessions on ultracold atomic gases served as a necessary reprieve for me that day.

Ultracold atoms, cooled to only a fraction of a degree above absolute zero, provide physicists with a clean and controllable platform for studying quantum many-body physics. At its heart, this physics is governed by interparticle correlations.

Seeing single atoms
Seeing single atoms A fluorescence image taken under a quantum gas microscope. Each dot is one atom (Courtesy: Candice Chua)

During my PhD, we measured two-body correlations and observed bosons spatially bunching together—unlike their antisocial fermionic counterparts. While the stereotypical physicist may be notoriously antisocial, the APS lanyard seemed to overturn that reputation.

Over dinner one evening, I requested a table for one. Only a moment later, I was joined by a physicist I’d never met before, and the evening unfolded behind pleasant chatter of 2D materials and the lack of vegetables in our travel diets.

Two tables down sat a professor whose work I admired. I’ll admit that I embarrassingly (or, more favourably, courageously) walked to the washroom so that I could pass by his table and say hello. I had met him once last year, but he didn’t remember me. So, I kept talking until he agreed that he remembered, and that it was nice to run into each other again. Whether true or not, I accepted it as a win. Without an APS lanyard, I probably would have avoided that conversation.

Single-atom resolution

On Thursday, a session titled “Novel imaging and quantum sensing technologies” caught my eye since I work with a quantum gas microscope. The microscope is a high-magnification imaging system that affords us the resolution of individual atoms. The microscopic information is far richer than what is obtained by a bulk imaging technique such as absorption.

Similarly, at the conference, I found the greatest value in individual conversations. Conversing with employees at the career fair, though exhausting, was far more effective than listening to panels on how to plan for careers that I couldn’t decide if I wanted.

By the end of the week, I started to recognize people I had already met over the few days prior. I saw every reunion or simple “Oh! Hi” as miraculous rather than a given, based on the size of the conference. People shared with me their personal journeys navigating the hardships and uncertainties of today’s world, others about the trade-offs and uncertainties in their experimental results. Some of the most fulfilling and deeply human conversations were the spontaneous ones that arose outside the doors of sessions that we had meant to be in.

When Friday rolled around, the city emptied as quickly as it had filled. For me, I retreated into the sunny Boulder mountains, mulling over the lingering resolution of singular people whose shared words and ideas were now intertwined with my own. Ignoring my fear of getting lost, I followed my instincts deeper into the dry heat of the afternoon, one step at a time.

Pressure quench increases superconducting transition temperature

Could a new pressure quenching technique help researchers move forward on the road to reaching room-temperature superconductivity? Researchers at the University of Houston are pinning their hopes on this approach and say they have already used it to achieve a record-high superconducting transition temperature (Tc) of 151 K at ambient pressure in a metastable phase of HgBa2Ca2Cu3O8+δ (or HBCCO) The phase remains stable for around at least three days when held at 77 K, although its Tc degrades when heated to above 200 K.

Achieving ambient-pressure room-temperature superconductivity remains the holy grail for scientists working in this field. This is because superconductors that work at ambient temperatures and pressures could revolutionize a host of application areas, including increasing the efficiency of electrical generators and transmission lines through lossless electricity transmission. They would also greatly simplify technologies such as magnetic resonance imaging (MRI) that rely on the generation or detection of magnetic fields.

While much progress has been made in the last decades, increasing the Tc often relies on squashing materials at extremely high pressure – usually in a device known as a diamond anvil cell (DAC). Some examples include the sulphide material H3S, which has a Tc of 203 K when compressed to pressures of 150 GPa and the cerium hydrides, CeH9 and CeH10, which boast high-temperature superconductivity at lower pressures of about 80 GPa with a Tc of around 100 K.

HBCCO is a high-temperature superconducting cuprate that has a Tc of 133 K at ambient pressure. This can be pushed to 164 K by applying a pressure of 31 GPa to it.

High-pressure-induced metastable superconducting phase

The high Tc of HBCCO is thought to come from the high electron density of states of a possible “van Hove singularity” associated with the two-dimensional CuO2 planes in it. In the new work, a team led by Ching-Wu Chu and Liangzi Deng of the Department of Physics and Texas Center for Superconductivity at the University of Houston decided to study a high-pressure-induced metastable superconducting phase in the material that they think might be able to form at ambient pressure as a result of this singularity (which leads to strong interactions between electrons) and/or other anomalies in the electronic energy spectrum.

To investigate further, the researchers developed a pressure-quench protocol to stabilize this metastable phase at ambient pressure. Their process involves first identifying the target phase in a DAC under high pressures of between 10–30 GPa. Next, the material is quenched (that is, the pressure is rapidly removed) at 4.2 K.

Chu and Deng confirmed that they had indeed isolated this phase and not another using synchrotron X-ray diffraction (at the 16-ID-B beamline of the Advanced Photon Source) before removing it from the cell. These measurements also show that the pressure-quenched phase at ambient pressure retains its original crystal structure, but possibly contains defects, generated under pressure and during quenching. The researchers think that these defects might help preserve the metastable high- Tc phase.

Thanks to their technique, they say they have achieved a hitherto unreported ambient-pressure Tc of 151 K.

Tiny samples

The experiments were far from easy, however, they say. The samples were extremely small (around just 50–80 microns in size), so handling them in high-pressure experiments is inherently challenging, explains Chu. Another major difficulty was preventing the electrical leads used for the resistivity measurements from breaking during the pressure-quenching process. Recovering the samples after quenching for more detailed analyses at ambient pressures was technically demanding too.

Looking ahead, the researchers say they would now like to better understand where the high Tc in HBCCO comes from – both under pressure before quenching and at ambient pressure after quenching. “We would also like to elucidate the mechanisms that lock in the high Tc phase at ambient pressure after quenching,” says Chu.

The impact of the new work, which is detailed in PNAS, might even extend beyond superconductivity, adds Deng. “Indeed, our approach could allow us stabilize quantum metastable states at ambient pressure that have enhanced or unique properties that only emerge under pressures. Based on our experimental results, using theoretical modelling and AI-driven approaches, we would like to identify different types of quantum materials that are suitable for pressure quenching.”

Researchers at CERN transport antiprotons by truck in world‑first experiment

Researchers at the CERN particle-physics lab have successfully transported antiprotons in a lorry across the lab’s main site. The feat, the first of its kind, follows a similar test with protons in 2024. CERN says the achievement is “a huge leap” towards being able to transport antimatter between labs across Europe.

Antimatter is almost identical to ordinary matter except that the electric charge and magnetic moment are reversed. But if equal amounts of matter and antimatter were created in the Big Bang, as is widely believed, they would have annihilated each other, leaving an empty universe. Physicists therefore suspect there are hidden differences that may explain why matter survived and antimatter all but disappeared.

CERN’s Baryon-Antibaryon Symmetry Experiment (BASE) experiment focuses on measuring the magnetic moment (or charge-to-mass ratio) of protons and antiprotons to search for such differences.

These measurements need to be extremely precise but this is difficult at CERN’s “Antimatter Factory”, which produces the antiprotons, due to inference from nearby equipment. To carry out more precise measurements, the team therefore needs a way of transporting the antiprotons to labs further afield.

To do so, in 2020 the BASE team began developing a device, known as BASE-STEP (for Symmetry Tests in Experiments with Portable Antiprotons), to store and transport antiprotons.

It works by trapping particles in a Penning trap composed of gold-plated cylindrical electrode stacks made from oxygen-free copper that is surrounded by a superconducting magnet bore operated at cryogenic temperatures.

The device, which also contains a carbon-steel vacuum chamber to shield the particles from stray magnetic fields, is then mounted on an aluminium frame. This allows it to be transported using standard forklifts and cranes and withstand the bumps and vibrations of transport.

In 2024, BASE researchers used the device to transport a cloud of about 105 trapped protons across CERN’s Meyrin campus for four hours.

After that feat, the researchers began to adjust BASE-STEP to handle antiprotons and yesterday the team successfully transported a trap containing a cloud of 92 antiprotons around the campus for 30 minutes, travelling up to 42 km/h.

With further improvements and tests, the team now hope to transport the antiprotons further afield. The first destination on the team’s list is the Heinrich Heine University (HHU) in Düsseldorf, Germany, which would take about eight hours.

“This means we’d have to keep the trap’s superconducting magnet at a temperature below 8.2 K for that long,” says BASE-STEP’s leader Christian Smorra. “So, in addition to the liquid helium , we’d need to have a generator to power a cryocooler on the truck. We are currently investigating this possibility.”

If possible to transport to HHU, physicists would then use the particles to search for charge-parity-time violations in protons and antiprotons with a precision at least 100 times higher than currently possible at CERN.

Heavier cousin of the proton discovered at the LHC

Researchers at the Large Hadron Collider (LHC) have discovered a new particle, the Ξcc⁺, (“Xi cc plus”), a heavier cousin of the proton. The particle’s fleeting existence had made it invisible for decades, but the upgraded LHCb detector captured it in just one year of data, opening a new window into the forces that hold quarks together.

Quarks are the fundamental building blocks of protons and neutrons, which in turn combine to form atomic nuclei. Protons themselves are made from two up quarks and one down quark, held together by the strong force. This is described by a sophisticated theory known as quantum chromodynamics (QCD). The Ξcc⁺ is unusual because it replaces the two up quarks with heavier charm quarks, keeping just one down quark.

“Up and down quarks are labels we give to distinguish the different types of quark,” Tim Gershon of the University of Warwick, told Physics World in an email. “In the Ξcc⁺, both up quarks are replaced by the heavier charm quark. Since the charm and up quarks differ only by their mass – in particular having the same charge – this provides an ideal way to test QCD,” explains Gershon who is spokesperson-elect for LHCb.

This quark content change makes the Ξcc⁺ roughly four times heavier than a proton. Its extremely short lifetime, less than a trillionth of a second, is why previous experiments could not detect it, despite the particle being produced frequently in LHC collisions.

Upgrade was crucial

“The key development that made the observation possible was the upgrade of the LHCb detector,” Gershon says. “We could observe the Ξcc⁺ in one year of data-taking, while we had not been able to do so in a decade of data collected with the original LHCb detector.”

The Ξcc⁺ appears briefly in proton–proton collisions before decaying into three lighter particles: a Λc⁺ baryon, a K⁻ meson, and a π⁺ meson. These decay further into five final particles, including a proton, two K⁻ mesons, and two π⁺ mesons. By reconstructing the trajectories of these particles, researchers saw a sharp signal corresponding to the existence of the Ξcc⁺ particle.

This observation also settles a long-standing question. Over twenty years ago, the SELEX experiment at Fermilab in the US reported hints of the particle. However, the signal could not be confirmed. The LHCb measurement provides a clear, unambiguous detection.

“Studies of particles containing two heavy quarks are very interesting for tests of the QCD binding mechanisms, and this observation provides important new data in that direction,” Gershon says.

The discovery relied on upgrades to the LHCb detector. A silicon pixel system called the Vertex Locator tracks particle paths with incredible precision, while a Ring Imaging Cherenkov system identifies particle types based on the light they emit. These improvements allow the detector to collect much larger amounts of data than before, making rare particle discoveries possible.

The discovery of the Ξcc⁺ is just the beginning. Physicists now aim to measure its properties in detail, including its lifetime and additional decay channels. Beyond this, they hope to find even heavier cousins, where one or both charm quarks are replaced by a beauty quark – called Ξbc and Ξbb respectively.

“These may be out of reach with the current LHCb detector – although we will try our best!” Gershon says. “But we do expect to be able to observe them with a future upgrade called LHCb Upgrade II. Unfortunately, the UK funding for this upgrade has recently been put in doubt due to decisions made at the UKRI funding agency. This latest result reiterates the uniqueness of LHCb – no other experiment can make these measurements – and the importance of finding a solution to be able to fund LHCb Upgrade II.”

Diamond films cool down electronics precisely where needed

A new technique for directly growing diamond layers in selected areas on technologically relevant substrates could help remove heat precisely where it is needed in electronic devices, improving their performance. The scalable technique, which relies on microwave plasma chemical vapour deposition, can create diamond patterns on silicon and gallium nitride across length scales ranging from microns to full 2-inch wafers.

Unwanted heat is a major problem in electronics, and the issue only gets worse as devices become smaller. Synthetic polycrystalline diamond could come into its own here, thanks to the material’s high thermal conductivity, which allows it to efficiently dissipate heat. The problem, however, is that diamond is very hard and chemically resistant. This makes it difficult to shape using the conventional “top-down” techniques employed to carve fully-grown diamond layers to the sizes required.

In the new work, a team of researchers led by materials scientists Xiang Zhang and Pulickel Ajayan and electrical and computer engineer Yuji Zhao of Rice University in the US turned to a bottom-up approach in which they build up diamond layer-by-layer using a plasma chemical vapour deposition technique. Their process, which is detailed in Applied Physics Letters, involves using microwave energy to ionize methane gas (CH4) so that it breaks down into its constituent carbon and hydrogen atoms. The carbon atoms then settle onto the substrate and assemble via a process that begins with nucleation. “Here, individual carbon atoms act as ‘seeds’ that other carbon atoms can latch on to,” explains Zhao.

Under these conditions, the researchers are able to control the thickness of the diamond by varying the growth time.

Controlling the seed location

To control the precise location of the carbon seeds, the team employed two techniques. The first was photolithography – a routine method in microelectronics that involves passing a light beam through a transmission mask to project an image of the mask’s light-absorption pattern onto a (usually silicon) wafer. The wafer itself is covered with a photosensitive polymer called a resist. Changing the intensity of the light leads to different exposure levels in the resist-covered material, making it possible to create small, finely detailed structures.

The approach, explains Zhao, is akin to using light to create a precise stencil, with the resulting structure acting as a mould for the diamond seeds. “Once the substrate wafers have been prepped, we spread a liquid containing nanodiamonds over their surface. These tiny specks then act as the starters for the diamond growth.”

The particle size of the nanodiamond seeds was 5–10 nm, which ensured a high nucleation density (estimated to be around 1011–1012 cm-2) for subsequent diamond growth, Zhao adds. High-magnification scanning electron microscopy revealed that the diamond films consisted of densely packed grains that were smaller than a micron and that the patterned diamond films were around 2.5–3.5 µm thick. Raman spectroscopy confirmed that a diamond film had formed across the entire patterned region and that it was highly crystalline.

To prove how versatile this approach was, the team decided to selectively fabricate complex geometries – for example, a diamond structure in the shape of an owl, which is the mascot of Rice University – on a gallium nitride substrate.

A different technique for larger wafers

This technique worked well for small-area patterns, but for larger wafers, a different approach was required, explains Zhao. Instead of conventional photoresist lithography, the team laminated a commercially available lapping film onto a silicon wafer that served as a removable masking layer. A standard laser cutter was then used to define the boundaries of the desired pattern by selectively cutting through the film.

Next, the engraved regions were peeled off, exposing the underlying substrate only in the predefined areas. “We then carried out nanodiamond seeding by spin-coating a nanodiamond suspension over the entire wafer,” says Zhao. “After solvent evaporation, we mechanically lifted off the remaining lapping film, removing the nanodiamond seeds from the masked regions to leave a patterned seed layer on the exposed substrate that diamond can then grow on.”

This approach allowed the researchers to scale up to a full 2-inch wafer.

“The key result is that we can grow diamond on selected, predefined areas on technologically relevant substrates,” Zhao tells Physics World. “This will allow diamond – the best bulk thermal conductor known – to be placed precisely where heat removal is needed in a device, making practical integration much more feasible. Indeed, we showed that our films when employed as heat spreaders on a silicon substrate can reduce the operating temperature by more than 23 °C compared to bare silicon.”

The team also discovered that smaller diamond islands were better at dissipating heat than a continuous diamond coating. “We found that the 50-micron diamond patterns achieved the most effective cooling because of their higher perimeter-to-area ratio,” Zhang explains. “These geometric features increase the density of the edge regions and help the heat dissipate more efficiently in three dimensions down into the silicon substrate.”

Thermal management is now a universal challenge – and is needed everywhere from AI GPUs and advanced logic (for example, FinFET technologies) to power electronics and photonics, Zhang adds. “As the global demand for AI accelerates, the associated power consumption and heat generation are becoming critical limits. Selective diamond integration offers a pathway to more efficient heat spreading across a broad range of technologies.”

Looking ahead, the researchers say they will now be working on direct device-level integration and making quantitative thermal measurements. They will also further optimize the material quality and interface engineering.

Superconductivity’s new contender

Researchers have experimentally observed a new kind of particle in transition‑metal dichalcogenide bilayers called doubly charged excitons, or quaternions. A single exciton is an electron bound to a hole, and combining an even number of fermions can create a boson with integer spin. In this system, one electron and three holes (or one hole and three electrons) bind together into a stable, doubly charged bosonic complex. Because bosons can occupy the same quantum state, these quaternions could in principle form a Bose-Einstein condensate, a collective phase in which all particles share a single macroscopic wavefunction. For charged bosons, such a condensate could carry electrical current with zero resistance, opening a pathway to a new kind of superconductivity.

The researchers confirmed the existence of quaternions through two key measurements. By continuously tuning the electron and hole densities, they observed the expected population behaviour of the bound state, and by applying magnetic fields, they identified the complex as a spin‑triplet. These signatures match theoretical predictions for a doubly charged exciton.

Unlike exciton or polariton condensates, a quaternion condensate is not expected to emit coherent light, and the experiments indeed show no signs of spectral narrowing or other coherence effects. Achieving condensation will require overcoming practical challenges, including heating from the optical pump and nonradiative Auger recombination at high densities, both of which raise the critical density for condensation. Better cooling and possible lateral confinement could help reach the required regime.

Although true Bose-Einstein condensation is not possible in an infinite two‑dimensional system, finite 2D systems can still undergo a transition that is effectively indistinguishable from condensation if the coherence length exceeds the system size. This makes it reasonable to search for superfluidity, and potentially superconductivity, in this platform. The strong long‑range Coulomb repulsion between quaternions also raises the possibility of entirely different quantum phases, such as a bosonic Wigner crystal or even a supersolid.

The establishment of these doubly charged exciton complexes in screened transition‑metal dichalcogenide bilayers opens a promising new direction in quantum materials research, with the real prospect of discovering a non‑BCS form of superconductivity (one that does not rely on the conventional Cooper‑pair mechanism) and other exotic states of matter.

Read the full article

Light-induced electron pairing in a bilayer structure

Qiaochu Wan et al 2026 Rep. Prog. Phys. 89 018003

Do you want to learn more about this topic?

Bose–Einstein condensation and indirect excitons: a review by Monique Combescot, Roland Combescot and François Dubin (2017)

A single theory for complicated quantum systems

Open quantum systems appear in quantum computers, quantum magnets and spintronics, but their behaviour is extremely difficult to model. The environment introduces memory effects (non‑Markovian dynamics) and strong system-bath interactions (non‑perturbative regimes), where most existing methods fail or require switching between entirely different techniques depending on the parameters. This research presents a single unified framework that can handle all these regimes for interacting quantum spins coupled to bosonic environments.

The approach combines Schwinger-Keldysh field theory with the two‑particle‑irreducible (2PI) effective action and crucially uses a 1/N expansion of Schwinger bosons rather than a perturbative expansion in the system-bath coupling. This allows the method to remain accurate even in strongly non‑perturbative regimes. The framework can compute advanced quantities such as multitime spin correlations, which are essential for understanding quantum phase transitions and nonequilibrium transport in quantum materials.

The authors benchmark their method against quasi‑exact tensor‑network simulations of the spin‑boson model, showing excellent agreement in the regimes where tensor‑network methods are applicable, and then apply it to more complex spin‑chain models with multiple baths where no other method currently works. Because it supports arbitrary spin value, geometry, dimensionality, and bath spectral function, the framework offers a general and computationally tractable route to simulating many‑body open quantum systems.

Overall, this work provides a powerful field‑theoretic tool for studying driven‑dissipative quantum systems, with applications ranging from quantum computing to quantum magnonics and spintronics.

Read the full article

Schwinger–Keldysh nonperturbative field theory of open quantum systems beyond the Markovian regime: application to spin-boson and spin-chain-boson models

Felipe Reyes-Osorio et al 2026 Rep. Prog. Phys. 89 018002

Do you want to learn more about this topic?

Keldysh field theory for driven open quantum systems by L M Sieberer, M Buchhold and S Diehl (2016)

Sunken nuclear submarine is leaking radioactive material intermittently

In April 1989 the Soviet Navy’s nuclear submarine Komsomolets caught fire while cruising 335 m beneath the surface of the Norwegian Sea. It was able to surface and 27 of 69 crew members survived the ordeal. The vessel then sank and now lies in 1680 m of water about 180 km off the coast of Norway’s Bear Island.

As well as being powered by a nuclear reactor, the Komsomolets is believed to contain two torpedo-mounted nuclear warheads. Not surprisingly, people are very concerned about the wreck and the possibility of radioactive materials leaking from the vessel.

Indeed, a Russian expedition in 1994 revealed that plutonium was leaking from one of the warheads. The following year, fractures in the hull and the torpedo tubes was sealed. Since then measurements taken near the Komsomolets suggest that any radioactive leakage is rapidly diluted by the surrounding water.

Now, scientists in Norway led by Justin Gwynn and Hilde Elise Heldal, have completed a comprehensive analysis of data taken by a 2019 survey of Komsomolets. The wreck’s marine environment was explored using Ægir 6000, which is a remote-controlled vehicle that is equipped with an array of cameras and other instruments and is capable of diving to 6000 m.

Writing in the Proceedings of the National Academy of Sciences, the team says analysis of seawater and sediment samples collected near the torpedo compartment reveals no evidence of plutonium being released from the warheads. However, analysis of samples from near a ventilation pipe show that radioactive material is being released intermittently from the nuclear reactor. By measuring the ratio of plutonium to uranium in the region, the team concluded that the fuel in the reactor is corroding.

Despite releases over the past three decades, Ægir 6000 found little evidence that radionuclides were accumulating in the region of the wreck – most likely because of the diluting effect of seawater.

The research is described in PNAS, where the team concludes, “Considering the global increase in military activities and geopolitical tensions, the fate of Komsomolets and the nuclear material within it can provide us with important insights as to impacts of any future accident involving nuclear powered vessels and nuclear weapons at sea”.

Electrosolvation force can act over long distances

Electrosolvation experiment
Electrosolvation Experimental setup and procedure for pair-potential measurements. (Courtesy: Rep. Prog. Phys.)

Two particles carrying electrical charge with the same sign should not attract each other, but in recent years, researchers have found that they can do this when they are dispersed in a liquid. A team at the University of Oxford in the UK has now discovered that the distance over which this counterintuitive “electrosolvation” force acts is much longer than theoretical models currently predict. They have also shown that the range of the force can depend on particle properties such as size and surface chemistry.

“The new finding reveals a missing piece in our understanding of electrostatic forces in liquids,” says physical chemist Madhavi Krishnan, who led this research study. “It is likely to reshape our understanding of how biological matter may self-organize and how molecules like DNA, RNA and proteins may naturally condense and cluster inside cells.”

In their work, Krishnan and colleagues used optical imaging to observe how pairs of charged micron-sized spheres with various surface coatings, such as DNA, polypeptides and anionic lipid bilayers (which make up cell membranes) interact in water.

Not a uniform medium

“Conventional electrostatic models treat the solvent as a uniform medium with a dielectric constant, but real liquids (such as water) cannot be described in this way because they form hydrogen bond networks and orient themselves around surfaces. Liquids also exhibit long-range correlations. All these properties may play a role in giving rise to an additional force which we call the electrosolvation force,” explains Krishnan.”

To be able to come up with a comprehensive understanding of the electrosolvation interaction, we have to dissect and carefully examine the phenomenology in question, she explains. A key feature of an interaction is its range. To measure the range of the attractive electrosolvation force accurately, Krishnan says that the students who carried out the experiments – her graduate student Sida Wang in particular – performed careful microscopy measurements on particles interacting with each other, observing individual pairs for periods of up to an hour and sometimes longer.

“We also performed exhaustive computer simulations to vet the measurements and estimate their accuracy,” Krishnan adds.

The researchers observed that DNA-coated particles exhibit particularly long-range attraction, which implies that the interaction depends not only on the solvent but also on the chemical and physical structure of the particles’ surface. This contrasts with the long-held view that the (Debye) screening length governing the interaction of charged particles in solutions depends only on the properties of the solvent medium.

Krishnan explains that the measured range of the attractive electrosolvation force can significantly exceed the nominal Debye length is to our knowledge not readily accounted for within any existing theoretical view and points to major gaps in our understanding of this very basic and fundamental question of how two charged particles interact in a liquid.. Indeed, it highlights the need for a more sophisticated view of the intervening medium than that offered by standard continuum electrostatics models.

“Current electrostatic models are incomplete”

“In short, anionic matter seems poised to attract; and the ability to either attract or repel in water, depending on the conditions, appears to be an intrinsic feature of negatively charged matter,” she tells Physics World. “It is entirely possible that the underlying mechanisms behind this process are broadly exploited in biology.”

The new work, which is detailed in Reports on Progress in Physics is the most recent in a series of investigations on the physics of interparticle interactions in the fluid phase, she says, and once again shows that current electrostatic models are incomplete – even under conditions in which they are expected to work well.

Looking ahead, the researchers say they would now like to examine the same interactions in bulk solution and compare these observations in the sedimented colloids studied in the present work.

Copyright © 2026 by IOP Publishing Ltd and individual contributors