Register – Page 6 – Chemistry and Physics

May 15, 2025May 28, 2025

Codoping double perovskites for single-component white-light-emitting diodes

A new paper published in Energy Material Advances explores Eu³⁺-Bi³⁺ codoping double perovskites for single-component white-light-emitting diodes.

“With lead-halide perovskites reaching a mature research stage approaching product marketing, concerns remain about the materials’ stability and the toxicity of lead-based salts,” said paper author Hongwei Song, professor at College of Electronic Science and Engineering, Jilin University.

Double perovskites with Cs₂AgInCl₆ composition, often doped with various elements, have been in the spotlight owing to their intriguing optical properties, namely, self-trapped exciton (STEs) emission and dopant-induced photoluminescence. This interest has sparked different synthesis approaches towards both crystals and nanocrystals, and the exploration of many alloy compositions with mono- and trivalent cations other than Ag⁺ and In³⁺.

Song explained that, in the development of lead-free perovskite materials, people’s first thought is to replace Pb element with a non-toxic element. In order to replace Pb in halide perovskite, researchers chose several low-toxic cations in the same period closest to it, such as Sn, Ge, Bi, Sb, In, etc., because they have a similar inactive shell s orbital.

This is the key to the unique photoelectric properties of perovskite materials. Lead-based perovskite materials have attracted great attentions in solid-state lighting area due to their high efficiency, high color rendering and tunable luminescence performance. This is both an opportunity and a challenge for the overall development of the photoelectric industry.

“Since the pioneering work on Cs₂AgInCl₆ in 2017 reported by Giustino et al. and Zhou et al. nearly simultaneously, many efforts have been devoted to its synthesis, modification of its composition, study of its electronic structure, optoelectronic properties, and applications. Recently, a record of white light emission with 86 % PLQY was achieved by Luo et al. via simultaneous alloying of Ag⁺ with Na⁺ and Bi³⁺ doping, marking an important milestone in the development of Cs₂AgInCl₆ related materials,” Song said.

“Despite several advantages, major issues with these lead halide perovskites remain their poor stability and toxicity. In order to solve such problems, various attempts have been made to reduce the toxicity of perovskites while still maintaining their efficient optical properties.”

The existence of Bi³⁺ ions decrease the excitation (absorption) energy, provides a new absorption channel and increases the energy transfer rate to Eu³⁺ ions. Through adjusting the Bi³⁺ and Eu³⁺ concentrations, a maximum photoluminescence efficiency (PLQY) of 80.1% is obtained in 6% Eu³⁺ and 0.5% Bi³⁺ co-doped Cs₂AgInCl₆ DPs.

“The energy transfer efficiency can be fitted with the decay rates under different Bi³⁺ doping concentrations. It can be seen that the energy transfer rate improves as a whole with the increase of the doping concentration of Bi³⁺, and the optimum energy transfer rate corresponding to the Bi³⁺ concentration is 0.5%. Next, we conducted PLQY test on the materials. For the undoped Cs₂AgInCl₆DPs, PLQY is only 0.5%, which dramatically increases to 20.1% after the addition of Bi³⁺. After [being] co-doped with Eu³⁺ and Bi³⁺ ions, PLQY continues to increase, and reaches the maximum of 80.1% when the Eu concentration reaches 6%,” Song said.

“Here, we propose a possible mechanism to describe Eu³⁺ emission in Bi/Eu3+: Cs₂AgInCl₆. Cs₂AgInCl₆ DP is a direct bandgap semiconductor. Bi³⁺ doping provides a new absorption channel for the material, which may be caused by the contribution of the Bi³⁺orbital in the band edge, breaking the STE-state compatibility ban transition, generating a new light absorption channel at a lower energy, and promoting the PLQY emitted by STE. For the Eu³⁺emission, we think there are two pathways. First, the energy transfer from STE to Eu³⁺ ions is possible as we have observed the Eu³⁺ emission in the Eu³⁺ doped Cs2AgInCl6 DPs. Second, the Eu3+ emission may mainly come from the energy transfer from Bi³⁺ ions to Eu³⁺ ions. The Bi³⁺ ions absorb the excitation light and transfer the energy from ¹P₁, ³P₂, ³P₁, ³P₀ levels of Bi³⁺ ions to ⁵D₃, ⁵D₂, ⁵D₁ and ⁵D₀ levels of Eu³⁺ ions. The characteristic emission of Eu³⁺ ions is then formed through ⁵D₀→⁷F_j(j=0,1,2,3) transitions.”

“Finally, we prepared the white light emitting diodes based on Bi³⁺ and Eu³⁺ codoped Cs₂AgInCl₆ DPs were fabricated with the optimum color rendering index of 89, the optimal luminous efficiency of 88.1 lm/W and a half-lifetime of 1493 h. This strategy of imparting optical functions to metal halide DPs may lead to future applications, such as optical fiber communications, daily lighting, military industry, displays, and other fields,” Song said.

More information: Tianyuan Wang et al, Eu³⁺-Bi³⁺ Codoping Double Perovskites for Single-Component White-Light-Emitting Diodes, Energy Material Advances (2023). DOI: 10.34133/energymatadv.0024

Provided by Beijing Institute of Technology Press Co., Ltd

May 14, 2025May 28, 2025

Innovative imaging technique uses the quantum properties of X-ray light

Innovative process uses the quantum properties of X-ray light — (a) Simplified sketch of the experimental setup. (b) Simulated intensity distribution in the focal plane with the phase grating. (c) Photon counts at the AGIPD, measured with the phase grating, averaged over 58 million patterns. This is a flat distribution without any apparent structural information. The mean photon count per pixel per frame was ⟨I⟩=0.0077. Credit: *Physical Review Letters* (2023). DOI: 10.1103/PhysRevLett.130.173201

An international team of researchers including scientists from FAU has, for the first time, used X-rays for an imaging technique that exploits a particular quantum characteristic of light. In their article, which has now been published in the journal Physical Review Letters, the researchers detail how this process could be used for imaging non-crystallized macromolecules.

The research team used the extremely short and very intensive X-ray pulses at the X-ray laser European EXFEL in Hamburg in order to generate fluorescence photons that arrived almost simultaneously at the detector—in a time window of less than one femtosecond (one quadrillionth of a second). By calculating the photon-photon correlations in the fluorescence of the illuminated copper atoms, it was possible to create an image of the light source.

On the atomic scale, the structures of materials and macromolecules are usually determined using X-ray crystallography. While this technique relies on coherent X-ray diffraction, the scattering of X-ray light can cause incoherent processes such as fluorescence emissions, which can dominate, even though they do not make a useful contribution to the diffraction measurement. Instead, they add a functionless haze or background to the measurement data.

As long ago as the 1950s, two British astronomers proved that it is possible to gain structural information from such self-luminous light sources, in their case it was the light from stars. Robert Hanbury Brown and Richard Twiss, whose method is known as intensity interferometry, opened a new door to the understanding of light and founded the field of quantum optics.

Recently, scientists from FAU, the Max Planck Institute for the Structure and Dynamics of Matter and the Deutsches Elektronen-Synchrotron (DESY) suggested that intensity interferometry could be adapted for atomic-resolution imaging using X-ray fluorescence. The challenge in extending this idea to X-rays is that the coherence time of the photons, which dictates the time interval available to perform photon–photon correlations, is extremely short. It is determined by the radiative decay time of the excited atom, which is about 0.6 femtoseconds for copper atoms.

Together with scientists from Uppsala University and the European XFEL, the group has now overcome that challenge by using femtosecond-duration XFEL pulses from that facility to initiate X-ray fluorescence photons within the coherence time. The team generated a source consisting of two fluorescing spots in a foil of copper and measured the fluorescence on a million-pixel detector placed eight meters away.

Only about 5,000 photons were detected on each illumination pulse, and the cumulative sum over 58 million pulses produced just a featureless uniform distribution. However, when the researchers instead summed photon-photon correlations across all images from the detector, a striped pattern emerged, which was analyzed like a coherent wave field to reconstruct an image of the fluorescent source, consisting of two well-separated spots of light.

The scientists now hope to combine this new method with conventional X-ray diffraction to image single molecules. Element-specific fluorescent light could expose substructures that are specific to certain atoms and even to certain chemical states. This could contribute to a better understanding of the functions of important enzymes such as those involved in photosynthesis.

More information: Fabian Trost et al, Imaging via Correlation of X-Ray Fluorescence Photons, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.173201

Journal information: Physical Review Letters

Provided by Friedrich–Alexander University Erlangen–Nurnberg

May 13, 2025May 28, 2025

Vinegar could be secret ingredient in fight against climate crisis

Chemical engineers at Monash University have developed an industrial process to produce acetic acid that uses the excess carbon dioxide (CO₂) in the atmosphere and has a potential to create negative carbon emissions.

Acetic acid is an important chemical used in several industrial processes and is an ingredient in household vinegar, vinyl paints and some glues. Worldwide industrial demand for acetic acid is estimated to be 6.5 million tons per year.

This world-first research, published in Nature Communications, shows that acetic acid can be made from captured CO₂ using an economical solid catalyst to replace the liquid rhodium or iridium based catalysts currently used.

Liquid catalysts require additional separation and purification processes. Using a solid catalyst made from a production method that doesn’t require further processing also reduces emissions.

Lead researcher Associate Professor Akshat Tanksale said the research could be a widely adopted practice for industry. “CO₂ is over abundant in the atmosphere, and the main cause of global warming and climate change. Even if we stopped all the industrial emissions today, we would continue to see negative impacts of global warming for at least a thousand years as nature slowly balances the excess CO₂,” Prof. Tanksale said.

“There is an urgent need to actively remove CO₂ from the atmosphere and convert it into products that do not release the captured CO₂ back into the atmosphere. Our team is focused on creating a novel industrially relevant method, which can be applied at the large scale required to encourage negative emissions.”

The research team first created a class of material called the metal organic framework (MOF) which is a highly crystalline substance made of repeating units of iron atoms connected with organic bridges.

They then heated the MOF in a controlled environment to break those bridges, allowing iron atoms to come together and form particles of a few nanometers in size.

These iron nanoparticles are embedded in a porous carbon layer, making them highly active while remaining stable in the harsh reaction conditions. This is the first time an iron based catalyst has been reported for making acetic acid.

From an industrial point of view, the new process will be more efficient and cost effective. From an environmental perspective, the research offers an opportunity to significantly improve current manufacturing processes that pollute the environment.

This means a solution to slow down or potentially reverse climate change while providing economic benefits to the industry from the sales of acetic acid products.

The researchers are currently in the process of developing the process for commercialization in collaboration with their industry partners as part of the Australian Research Council (ARC) Research Hub for Carbon Utilization and Recycling.

More information: Waqar Ahmad et al, Aqueous phase conversion of CO2 into acetic acid over thermally transformed MIL-88B catalyst, Nature Communications (2023). DOI: 10.1038/s41467-023-38506-5

Journal information: Nature Communications

Provided by Monash University

May 12, 2025May 28, 2025

Demystifying vortex rings in nuclear fusion and supernovae

Better understanding the formation of swirling, ring-shaped disturbances—known as vortex rings—could help nuclear fusion researchers compress fuel more efficiently, bringing it closer to becoming a viable energy source.

The model developed by researchers at the University of Michigan could aid in the design of the fuel capsule, minimizing the energy lost while trying to ignite the reaction that makes stars shine. In addition, the model could help other engineers who must manage the mixing of fluids after a shock wave passes through, such as those designing supersonic jet engines, as well as physicists trying to understand supernovae.

“These vortex rings move outward from the collapsing star, populating the universe with the materials that will eventually become nebulae, planets and even new stars—and inward during fusion implosions, disrupting the stability of the burning fusion fuel and reducing the efficiency of the reaction,” said Michael Wadas, a doctoral candidate in mechanical engineering at U-M and corresponding author of the study.

“Our research, which elucidates how such vortex rings form, can help scientists understand some of the most extreme events in the universe and bring humanity one step closer to capturing the power of nuclear fusion as an energy source,” he said.

Nuclear fusion pushes atoms together until they merge. This process releases several times more energy than breaking atoms apart, or fission, which powers today’s nuclear plants. Researchers can create this reaction, merging forms of hydrogen into helium, but at present, much of the energy used in the process is wasted.

Part of the problem is that the fuel can’t be neatly compressed. Instabilities cause the formation of jets that penetrate into the hotspot, and the fuel spurts out between them—Wadas compared it to trying to squish an orange with your hands, how juice would leak out between your fingers.

Vortex rings that form at the leading edge of these jets, the researchers have shown, are mathematically similar to smoke rings, the eddies behind jellyfish and the plasma rings that fly off the surface of a supernova.

Perhaps the most famous approach to fusion is a spherical array of lasers all pointing toward a spherical capsule of fuel. This is how experiments are set up at the National Ignition Facility, which has repeatedly broken records for energy output in recent years.

The energy from the lasers vaporizes the layer of material around the fuel—a nearly perfect, lab-grown shell of diamond in the latest record-setter in December 2022. When that shell vaporizes, it drives the fuel inward as the carbon atoms fly outward. This generates a shockwave, which pushes the fuel so hard that the hydrogen fuses.

While the spherical fuel pellets are some of the most perfectly round objects humans have ever made, each has a deliberate flaw: a fill tube, where the fuel enters. Like a straw stuck in that crushed orange, this is the most likely place for a vortex-ring-led jet to form when the compression starts, the researchers explained.

“Fusion experiments happen so fast that we really only have to delay the formation of the jet for a few nanoseconds,” said Eric Johnsen, an associate professor of mechanical engineering at U-M, who supervised the study.

The study brought together the fluid mechanics expertise of Wadas and Johnsen as well as the nuclear and plasma physics knowledge in the lab of Carolyn Kuranz, an associate professor of nuclear engineering and radiological sciences.

“In high-energy-density physics, many studies point out these structures, but haven’t clearly identified them as vortex rings,” said Wadas.

Knowing about the deep body of research into the structures seen in fusion experiments and astrophysical observations, Wadas and Johnsen were able to draw on and extend that existing knowledge rather than trying to describe them as completely new features.

Johnsen is particularly interested in the possibility that vortex rings could help drive the mixing between heavy elements and lighter elements when stars explode, as some mixing process must have occurred to produce the composition of planets like Earth.

The model can also help researchers understand the limits of the energy that a vortex ring can carry, and how much fluid can be pushed before the flow becomes turbulent and harder to model as a result. In ongoing work, the team is validating the vortex ring model with experiments.

The research is published in the journal Physical Review Letters.

More information: Michael J. Wadas et al, Saturation of Vortex Rings Ejected from Shock-Accelerated Interfaces, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.194001

Journal information: Physical Review Letters

Provided by University of Michigan

May 11, 2025May 28, 2025

Researchers analyze THC in breath of cannabis smokers

Most states in the U.S. allow people to use cannabis for medical or recreational purposes. Yet all states want their roadways to be safe. A breathalyzer that can accurately identify people who recently smoked cannabis might help them keep impaired drivers off the road—if such a device existed.

But developing a breathalyzer for cannabis is far more difficult than for alcohol, which people exhale in large amounts when drinking. In contrast, the intoxicating component of cannabis, called THC, is thought to be carried inside aerosol particles that people exhale. The total volume of aerosols can be very small, making it difficult to accurately measure their THC content. Currently, there is no standard method for doing this.

Now, researchers at the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder have conducted a study in which they collected breath samples from people both before and after they smoked high-THC cannabis, aka marijuana, and used laboratory instruments (not a handheld device) to measure the amount of THC in their breath.

The goal of this study, published in the Journal of Breath Research, was to begin developing a protocol that yields reproducible results—a necessary step toward a reliable, validated field-based method.

The samples collected before people smoked were important because THC can persist in the bodies of people who frequently use cannabis for a month or more, long after the effects of the drug have worn off.

“One key question that we cannot yet answer is whether breath measurements can be used to distinguish between a person who uses cannabis regularly but hasn’t done so lately, and someone who consumed an hour ago,” said NIST supervisory chemical engineer and study author Tara Lovestead. “Having a reproducible protocol for breath measurements will help us and other researchers answer that question.”

The breath samples were collected in a mobile lab—a comfortably appointed white van that would park conveniently outside participants’ homes. This mobile pharmacology lab was developed by researchers at University of Colorado Boulder, including Cinnamon Bidwell, an assistant professor of psychology and neuroscience and a co-author of the study.

In addition, all participants purchased and used a consistent kind of high-THC cannabis prepared by a licensed dispensary in Boulder, Colorado. This study design allowed the authors to conduct their research without handling high-THC cannabis or otherwise running afoul of federal laws.

At the appointed time, participants popped into the van, gave their pre-use breath sample and also provided a blood sample. They then went back into their residence, smoked cannabis according to their usual custom and returned immediately to the van to provide a second blood sample. Since THC concentrations in blood spike immediately after consuming the drug, researchers compared the before-and-after blood samples to confirm that the participants had in fact just used it. An hour later, the participants gave their second breath sample.

Participants provided breath samples by blowing into a tube containing an “impaction filter” that captured aerosols from their breath. Later in the lab, the researchers extracted the material caught in the filter and measured the concentration of THC and other cannabis compounds using liquid chromatography with tandem mass spectrometry, a laboratory technique that identifies compounds and measures their amount.

Because this was a protocol development study that involved only 18 participants, the results of the analysis do not carry statistical weight. However, they do highlight the need for further study.

“We expected to see higher THC concentrations in the breath samples collected an hour after people used,” Lovestead said. However, THC levels spanned a similar range across pre-use and post-use samples. “In many cases, we would not have been able to tell whether the person smoked within the last hour based on the concentration of THC in their breath.”

“A lot more research is needed to show that a cannabis breathalyzer can produce useful results,” said NIST materials research engineer and co-author Kavita Jeerage. “A breathalyzer test can have a huge impact on a person’s life, so people should have confidence that the results are accurate.”

More information: Kavita M Jeerage et al, THC in breath aerosols collected with an impaction filter device before and after legal-market product inhalation—a pilot study, Journal of Breath Research (2023). DOI: 10.1088/1752-7163/acd410

Journal information: Journal of Breath Research

Provided by National Institute of Standards and Technology

May 10, 2025May 28, 2025

Quantum cutting, upconversion, and temperature sensing help with thermal management in silicon-based solar cells

by Chinese Academy of Sciences

Quantum cutting, upconversion, and temperature sensing help with thermal management in silicon-based solar cells — Short wavelength absorption of Er³⁺ in NaY(WO₄)₂. Excitation spectra for NaY(WO₄)₂:Er³⁺ doped with different Er³⁺ concentrations by monitoring 552 nm emission. Credit: *Light: Science & Applications* (2024). DOI: 10.1038/s41377-023-01365-2

Introducing light conversion materials into silicon-based photovoltaic devices is an effective way to improve their photoelectric conversion efficiency. Light conversion materials include quantum cutting materials and upconversion materials.

The purpose of introducing quantum cutting materials is to divide a short-wavelength photon into two or more photons that can join the photoelectric conversion in silicon-based photovoltaic devices. Introducing upconversion materials is done to combine two or more infrared photons into one photon that can also be used for photoelectric conversion in silicon-based photovoltaic devices.

The introduction of light conversion materials can improve photoelectric conversion efficiency without changing the performance of silicon-based solar cells themselves. This method can greatly reduce the technical difficulty of improving the efficiency of silicon-based photovoltaic systems. In addition, silicon-based photovoltaic devices are exposed to sunlight, so their temperature must be managed. Managing this temperature necessitates measuring it in advance.

However, it is possible that if three materials that can individually achieve quantum cutting, upconversion, and temperature sensing are simultaneously introduced into silicon-based solar cells, it will lead to difficulties in solar cell structure design and unnecessary increase in the product costs. Therefore, finding and developing high-performance materials that combine the above three functions is a challenge.

In a new paper published in Light: Science & Applications, researchers from the School of Science, Dalian Maritime University reports that they have achieved highly efficient photo split, nearly pure infrared upconversion emission, and suitable temperature sensing for thermal management in silicon-based solar cells by adjusting the doping concentrations of Er³⁺ and Yb³⁺ in NaY(WO₄)₂ phosphor.

The work reveals that this all-in-one material is an excellent candidate for application in silicon-based solar cells for improving their photoelectric conversion efficiency and enhancing their heat management.

An in-depth understanding of the quantum cutting mechanism is significant for designing and assessing the quantum cutting materials. However, in many cases, quantum cutting processes are complicated. In this work, the authors carefully decrypted the photo-splitting steps in Er³⁺/Yb³⁺ co-doped NaY(WO₄)₂ to assist the doping-concentration-dependent spectroscopy and fluorescence dynamics.

The team states, “Based on the optical spectroscopic analyses, the quantum cutting mechanism was discovered, and the photon splitting process includes two-step energy transfer processes, namely, ⁴S_3/2+²F_7/2 ⁴I_11/2 +²F_5/2 and ⁴I_11/2 + ²F_7/2 ⁴I_15/2 + ²F_5/2.”

The quantum cutting efficiency can be confirmed experimentally and theoretically. In the ideal case, the measured quantum cutting efficiency is also defined as the internal quantum efficiency, but it is different from the traditional definition of internal quantum efficiency. The measuring technique for the quantum efficiencies is still not satisfactory since the measuring results are complicated by too many uncontrollable factors.

Therefore, the theoretical internal quantum cutting efficiency becomes significant. The authors claim, “The quantum cutting mechanism was discovered by the optical spectroscopic analyses, and the quantum cutting efficiencies were calculated in assistance of Judd-Ofelt theory, Föster-Dexter theory, energy gap law.” The authors estimated the internal quantum cutting efficiencies for NaY(WO₄)₂: Er³⁺/Yb³⁺ by taking radiative transitions, non-radiative transitions, and energy transfers into account, and achieved an efficiency as high as 173%.

Another important point of this work is that the researchers achieved nearly pure near-infrared emission of Yb³⁺.

The team observes, “These upconversion mechanisms tell us that both Er³⁺ and Er³⁺/Yb³⁺ doped NaY(WO₄)₂ phosphors exhibit strong near-infrared emissions from ⁴I_11/2⁴I_15/2 of Er³⁺ and ²F_5/2²F_7/2 of Yb³⁺ that indicates the studied phosphors are good light conversion candidate[s] for silicon-based solar cell applications.”

More information: Duan Gao et al, Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO4)2:Er3+/Yb3+ with thermal management capability for silicon-based solar cells, Light: Science & Applications (2024). DOI: 10.1038/s41377-023-01365-2

Provided by Chinese Academy of Sciences

May 9, 2025May 28, 2025

Researchers develop interfacial charge modification strategy to enhance photocatalytic water oxidation

Water oxidation reaction involves a four-electron and four-proton transfer process, which requires an uphill energy transformation and limits the efficiency of the overall photocatalytic water splitting reaction.

Although loading appropriate water oxidation cocatalysts can enhance the performance of water oxidation reactions, the interfacial barrier between the semiconductor and the water oxidation cocatalyst can impede the transfer and utilization of photogenerated charges.

Recently, a research team led by Profs. Li Can and Li Rengui from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has developed a strategy to controllably assemble a charge-transfer mediator in photocatalysis, which could increase surface charge-transfer efficiency and photocatalytic water oxidation activity. The study was published in Angewandte Chemie International Edition on March 23.

Inspired by natural photosynthesis, the researchers employed partially oxidized graphene (pGO) as a charge-transferring mediator on the hole-accumulating facets of lead chromate (PbCrO₄) photocatalyst. The pGO could be selectively assembled on the hole-accumulating facets of PbCrO₄ by an ultrasonic deposition process, and cobalt-complex Co₄O₄ molecules could be anchored on the pGO as water oxidation cocatalyst.

Based on techniques such as surface photovoltage spectroscopy, they confirmed that introducing the pGO charge transfer mediator between the hole-accumulation facets of PbCrO₄ and Co₄O₄ molecules could effectively suppress charge recombination at the interface, thus prolonging the lifetime of photogenerated charges and enhancing photocatalytic water oxidation performance.

“The strategy of rationally assembling charge transfer mediator provides a feasible way for accelerating charge transfer and charge utilization in semiconductor photocatalysis,” said Prof. Li Rengui.

More information: Wenchao Jiang et al, Graphene Mediates Charge Transfer between Lead Chromate and a Cobalt Cubane Cocatalyst for Photocatalytic Water Oxidation, Angewandte Chemie International Edition (2023). DOI: 10.1002/anie.202302575

Journal information: Angewandte Chemie International Edition

Provided by Chinese Academy of Sciences

May 8, 2025May 28, 2025

The exciting possibilities of tiny, twisted superconductors

Transporting energy is costly. When a current runs through conductive materials, some of the energy is lost due to resistance as particles within the material interact—just notice the warmth from your phone or laptop. This energy loss presents a hurdle to the advancement of many technologies and scientists are searching for ways to make superconductors that eliminate resistance.

Superconductors can also provide a platform for fault-tolerant quantum computing if endowed with topological properties. An example of the latter is the quantum Hall effect where the topology of electrons leads to universal, “quantized,” resistance with accuracy up to one part in a billion, which finds uses in meteorology. Unfortunately, the quantum Hall effect requires extremely strong magnetic fields, typically detrimental to superconductivity. This makes the search for topological superconductors a challenging task.

In two new papers in Physical Review Letters and Physical Review B UConn Physicist Pavel Volkov and his colleagues propose how to experimentally manipulate the quantum particles, called quasiparticles, in very thin layers of ordinary superconductors to create topological superconductors by slightly twisting the stacked layers.

Volkov explains there is a lot of research being done on ways to engineer materials by stacking layers of two-dimensional materials together:

“Most famously, this has been done with graphene. Stacking two graphene layers in a particular way results in a lot of interesting new phenomena. Some parallel those in high-temperature superconductors, which was unexpected because, by itself, graphene is not superconducting.”

Superconductivity happens when a material conducts current without any resistance or energy loss. Since resistance is a challenge for many technologies, superconducting materials have the potential to revolutionize how we do things, from energy transmission to quantum computing to more efficient MRI machines.

However, endowing superconductors with topological properties is challenging, says Volkov, and as of now, there are no materials that can reliably perform as topological superconductors.

The researchers theorize that there is an intricate relation between what happens inside the twisted superconductor layers and a current applied between them. Volkov says the application of a current makes the quasiparticles in the superconductor behave as if they were in a topological superconductor.

“The twist is essentially determining the properties, and funnily enough, it gives you some very unexpected properties. We thought about applying twisting to materials that have a peculiar form of superconductivity called nodal superconductivity,” says Volkov.

“Fortunately for us, such superconductors exist and, for example, the cuprate high-temperature superconductors are nodal superconductors. What we claim is that if you apply a current between two twisted layers of such superconductors, it becomes a topological superconductor.”

The proposal for current-induced topological superconductivity is, in principle, applicable at any twist angle, Volkov explains, and there is a wide range of angles that optimize the characteristics, which is unlike other materials studied so far.

“This is important because, for example, in twisted bilayer graphene, observation of interesting new phenomena requires to align the two layers to 1.1 degrees and deviations by .1 degrees are strongly detrimental. That means that one is required to make a lot of samples before finding one that works. For our proposal this problem won’t be as bad. If you miss the angle even by a degree, it’s not going to destroy the effect we predict.”

Volkov expects that this topological superconductor has the potential to be better than anything else currently on the market. Though one caveat is they do not know exactly what the parameters of the resulting material will be, they have estimates that may be useful for proof of principle experiments.

The researchers also found unexpected behaviors for the special value of twist angle.

“We find a particular value of the angle, the so-called ‘magic angle,’ where a new state should appear—a form of magnetism. Typically, magnetism and superconductivity are antagonistic phenomena but here, superconductivity begets magnetism, and this happens precisely because of the twisted structure of the layers.” says Volkov.

Demonstrating these predictions experimentally will bring more challenges to overcome, including making the atoms-thick layers better themselves and determining the difficult-to-measure parameters, but Volkov says there is a lot of motivation behind developing these highly complex materials.

“Basically, the main problem so far is that the candidate materials are tricky to work with. There are several groups around the world trying to do this. Monolayers of nodal superconductors, necessary for our proposal have been realized, and experiments on twisted flakes are ongoing. Yet, the twisted bilayer of these materials has not yet been demonstrated. That’s work for the future.”

These materials hold promise for improving materials we use in everyday life, says Volkov. Things already in use that take advantage of the topological states include devices used to set resistance standards with high accuracy. Topological superconductors are also potentially useful in quantum computing, as they serve as a necessary ingredient for proposals of fault-tolerant qubits, the units of information in quantum computing. Volkov also emphasizes the promise topological materials hold for precision physics,

“Topological states are useful because they allow us to do precision measurements with materials. A topological superconductor may allow us to perform such measurements with unprecedented precision for spin (magnetic moment of electron) or thermal properties.”

More information: Pavel A. Volkov et al, Current- and Field-Induced Topology in Twisted Nodal Superconductors, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.186001

Pavel A. Volkov et al, Magic angles and correlations in twisted nodal superconductors, Physical Review B (2023). DOI: 10.1103/PhysRevB.107.174506

Journal information: Physical Review Letters , Physical Review B

Provided by University of Connecticut

May 7, 2025May 28, 2025

Researchers investigate involuntary THC exposure in homes

living room — Credit: Pixabay/CC0 Public Domain

University of Toronto researchers are investigating exposure to second-hand—and even third-hand—marijuana smoke in homes, including the THC that can collect on floors and surfaces.

The researchers, in Faculty of Applied Science & Engineering, have published a new study that models how THC—the main psychoactive ingredient in cannabis—behaves and transforms once it is released in an indoor environment. The study is published in the journal Environmental Science: Atmospheres.

The model enables researchers to explore mitigation strategies that could reduce involuntary exposure levels.

“We began our research on tetrahydrocannabinol (THC), which is the psychoactive part of cannabis that causes intoxication, because when we looked at second- and third-hand smoke, we started to see how much involuntary exposure happens,” says Amirashkan Askari, a Ph.D. candidate in department of chemical engineering and applied chemistry.

Askari co-authored the study with U of T Engineering Associate Professor Arthur Chan and Frank Wania, a professor in the department of physical and environmental sciences at U of T Scarborough.

Between April 2021 and March 2022, Canadians spent $4 billion on regulated, adult-use cannabis, according to Statistics Canada. Dried cannabis accounted for 71.1 percent of sales, indicating that smoking is the most popular method of consumption.

“Any type of smoking, whether it is tobacco or cannabis, leaves behind a suite of pollutants that can remain in homes,” says Chan. “We now have sufficient chemical knowledge about THC to model its behavior in a typical indoor environment.”

Moreover, involuntary THC exposure can continue long after smoking has ceased. This is due to THC’s large and complex chemical structure, which has a strong tendency to stick to surfaces and create third-hand exposure,” says Askari.

“There are a lot of surfaces indoors—tables, chairs and floors. When you calculate the ratio of surfaces to volume, it is quite elevated compared to the outdoors,” he says. “So, when a pollutant is emitted, it always has the chance to migrate from air to surfaces.

“Involuntary exposure to pollutants starts to become more important when we consider infants and children who reside in homes where this smoking takes place. Children tend to touch surfaces more than adults as they crawl or play; they are also known to frequently put their hands or objects in their mouth.”

Askari used a time-dependent indoor mass-balance model to forecast the level of human exposure to THC. The study also examined the effectiveness of mitigating strategies—from air purifiers to surface cleaners—in reducing second- and third-hand exposure from marijuana smoke.

The model was run for one simulated year under the assumption that THC from single-stream smoke (the lighted end) of a burning cannabis cigarette was emitted into the indoor air for one hour daily.

By modeling the exposure level of an adult and a toddler (who were distinguished by body weight) Askari predicted that residents of all ages who are present during smoking sessions are vulnerable to high levels of involuntary second-hand THC.

The exposure analysis also found that carpet and flooring materials were significant reservoirs of THC that migrated from air to surface. Since younger children are prone to object mouthing—a common part of infant and toddler development—this makes them especially sensitive to THC from third-hand exposure. These results, the study concludes, highlight the importance of preventing children from accessing spaces where cannabis smoking takes place, both during and after smoking.

“When it comes to improving indoor air quality, the best way to degrade air pollutants is to shut down the source,” says Askari. “But if our aim is to suppress it, we found the most effective measures were strategies that target the air particles directly. So, if you have an air purifier unit that filters particulate matter from the air, that will reduce that exposure significantly.”

While the researchers’ initial study used computer simulation, the second phase of this cannabis and indoor air pollution research involves experiments in collaboration with the Centre for Addiction and Mental Health (CAMH).

“We had volunteers come in and either smoke or vape cannabis,” says Askari. “We measured the composition of air in real time—while they were consuming the cannabis—so we could see what happens to the air quality. We also did comparisons between smoking and vaping.”

The results from this second study have not been published, but the team hopes this research will help individuals and policymakers better understand how this source of indoor air pollution impacts the health of communities.

“We hope that people will start paying more attention to indoor air quality, not just during these high-emitting activities, but also long after they are over,” Chan says. “Keeping our homes well-ventilated is very effective at lowering our exposures, even if it is just for a brief period of time during and after smoking.”

More information: Amirashkan Askari et al, Modeling the fate and involuntary exposure to tetrahydrocannabinol emitted from indoor cannabis smoking, Environmental Science: Atmospheres (2023). DOI: 10.1039/D2EA00155A

Provided by University of Toronto

May 6, 2025May 28, 2025

Precision mass measurements of nuclei reveal properties of neutron star

Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) and their collaborators have measured the masses of several key nuclei with high precision by employing the most advanced storage-ring mass spectrometry technique. Using the new data, they investigated X-ray bursts on the surface of a neutron star, setting constraints on the properties of neutron stars from a new perspective. The study was published in Nature Physics.

Neutron stars are considered to be the densest objects after black holes. Type-I X-ray bursts, among the brightest stellar objects frequently observed in the sky by space-based telescopes, are violent thermonuclear explosions occurring on the surfaces of neutron stars.

Due to the strong gravity of a neutron star, hydrogen- and helium-rich matter from a companion star is accreting on the surface of the neutron star for hours or days before igniting thermonuclear burning. The explosion lasts for 10 to 100 seconds, causing a bright X-ray burst. These frequent X-ray bursts offer an opportunity to study the properties of neutron stars.

The bursts are powered by a nuclear reaction sequence known as the rapid proton capture nucleosynthesis process (rp-process), which involves hundreds of exotic neutron-deficient nuclides. Among them, the waiting-point nuclides, including germanium-64, play a decisive role. “Germanium-64, like a crossroad on the path of nuclear reaction processes, is an important congested section encountered when the nuclear reaction proceeds to the medium mass region. The masses of the relevant nuclei are decisive in setting the process path and thereby the X-ray flux produced,” explained Zhou Xu, the first author of this paper and a Ph.D. student at IMP.

Therefore, precision mass measurements of the nuclei around germanium-64 are essential for understanding X-ray bursts and the properties of neutron stars. However, due to the extremely low production yield, it has been very challenging to measure the masses of these short-lived nuclei.

After more than ten years of effort, the researchers from the Storage Ring Nuclear Physics Group at IMP have developed a new ultrasensitive mass spectrometry technique at the Cooler Storage Ring (CSR) of the Heavy Ion Research Facility in Lanzhou (HIRFL), which is called Bρ-defined isochronous mass spectrometry (Bρ-IMS). It quickly and efficiently measures short-lived nuclei with extreme low production yield.

“Our experiment is capable of precisely determining the mass of a single nuclide within a millisecond after its production, and it is essentially background free in the measured spectrum,” said Prof. Wang Meng from IMP.

The researchers precisely measured the masses of arsenic-64, arsenic-65, selenium-66, selenium-67 and germanium-63. The masses of arsenic-64 and selenium-66 are the first experimental results in the world, and the mass precision of the others have all been improved. With the newly measured masses, all nuclear reaction energy related to the waiting point nucleus germanium-64 has been experimentally determined for the first time.

The researchers used the new masses as inputs for X-ray burst model calculations. They found that the new data lead to changes in the rp-process path. As a result, the X-ray burst light curve on the surface of the neutron star has an increased peak luminosity and a prolonged tail duration.

By comparing model calculations with the observed X-ray bursts of GS 1826-24, the researchers found that the distance from Earth to the burster should be increased by 6.5%, and the neutron star surface gravitational redshift coefficient needs to be reduced by 4.8% to match astronomical observations, which indicates that the density of the neutron star is lower than expected. In addition, the composition changes of the rp-process reaction products revealed that the temperature of the outer shell of the neutron star should be higher than generally believed after the X-ray burst.

The property of neutron stars is a frontier physics research topic of great importance. “Through precise nuclear mass measurement, we obtained a more accurate X-ray burst light curve on the surface of the neutron star. By comparing it with astronomical observations, we set constrains on the relationship between the mass and radius of the neutron star from a new perspective,” said Prof. Zhang Yuhu from IMP.

More information: X. Zhou et al, Mass measurements show slowdown of rapid proton capture process at waiting-point nucleus 64Ge, Nature Physics (2023). DOI: 10.1038/s41567-023-02034-2

Journal information: Nature Physics

Provided by Chinese Academy of Sciences