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Not all Renewable Energy is Created Equal

Daniel Morton — Fri, 31 Jul 2026 18:20:53 +0000

Not all Renewable Energy is Created Equal Daniel Morton Fri, 07/31/2026 - 12:20

Daniel Morton

Solar panels in California and wind turbines in Indiana both produce clean, non-polluting electricity, but one of them consistently delivers greater benefits to the environment, according to new research from RASEI Fellow Dan Kaffine.

On paper, a megawatt-hour is just a megawatt-hour, it will charge your phone or run your dishwasher the same way, regardless of the source. However, the value to, or impact on, the environment is not fixed. It depends almost entirely on what power plant it replaces. A new wind turbine only helps the climate and local air quality to the extent that it pushes a more polluting plant offline. If instead it is just competing with another clean energy source, the environmental benefit effectively disappears.

Think of it like carpooling. Taking one car off the road does a lot more good during a gridlocked rush hour than it does taking it off an empty highway at 3 AM. Same action, but vastly different impact, depending entirely on what else is going on in the system. In many cases, renewable energy works the same way. A wind turbine spinning at 3 AM in Indiana is like carpooling during rush hour, it is likely pushing a coal plant offline, cutting real emissions. That same turbine spinning at 3 PM in California, when the grid is already flush with solar generated electricity, is more like carpooling on an empty road; the energy is clean, but it is not actually reducing emissions.

To get a more accurate picture of the environmental value of energy, and how it changes across time and location, required significant analysis. “You can have a technically identical megawatt-hour of energy from a wind farm or a solar plant” explains Kaffine “but the value to society of that megawatt-hour, from an environmental standpoint, can be very different.” Kaffine and Fell show that the magnitude of a renewable energy source’s environmental value hinges on which “marginal” power plant it displaces, and that this displacement can actually follow predictable patterns. The paper that appears in The Energy Journal, explores the different factors and implications at play in this determination. The team explored a range of different scenarios. The analysis included how location and energy transmission constraints impact which generators are offset, it looked at how the timing of renewable production plays a role and how policies such as renewable production subsidies and regulations around Green Hydrogen impact the energy value of new projects. Through this detailed analysis some headline findings emerged.

The time of day matters. Displace power at night and you are more likely to displace a coal plant. Displace it midday, and you are most likely competing with gas, or worse, another renewable source.

Location is key. Wind in the coal-heavy upper Midwest is likely offsetting coal near population centers, delivering real air-quality improvements. Wind or solar in California is more often competing with the state’s already abundant renewable sources.

Understanding that the value varies is essential for building policies that drive change in the grid. In California, wind turbines that turn in the middle of a sunny day often don’t displace fossil fuels at all, instead it forces solar generation to be curtailed. “You don’t want to be subsidizing a wind generator that is just bumping off solar in the middle of the day” explains Kaffine. Until we recognize that we need to take the environmental value into account, and install renewable generators in locations where they can displace the most polluting plants, then we are not maximizing the possible change.

Currently, most environmental policy treats renewable energy as fungible: a megawatt-hour is a megawatt-hour. Production tax credits pay a flat rate per MWh of wind or solar, with no consideration of when or where it is generated. Many renewable portfolio standards just require a fixed percentage of power to come from renewables, with little attention to their environmental value. Renewable Energy Credits (RECs), which are the tradable certificates that are woven into many of these programs are priced simply on energy output, and no concern about environmental value.

This kind of flat-rate logic assumes that all renewable energy generation delivers roughly equivalent environmental benefit. Kaffine and Fell’s work shows how this assumption breaks down when you look deeper into the details.

Two ideas emerge from this study as the researchers look forward. First, you can only manage what you can measure. Regulators need something close to real-time data on which power plant is getting displaced at any given moment. Historical estimates are not good enough. The infrastructure required for such measurements is starting to emerge. For example, grid operators in the upper Midwest have begun piloting dashboards that track local marginal emissions, using the same framework that electricity markets already employ to track local marginal prices.

Second, integrating this data into policy tools. Currently, subsidies don’t distinguish quality. A wind farm gets the same subsidy whether it is offsetting a 40-year old coal plant, or just curtailing a neighboring solar array. Think about how food labels distinguish an organic, farm-identified chicken breast from a generic one. This gives buyers, in the case of energy the regulators and utilities, a way to tell higher-impact renewable energy apart from lower-impact renewable energy, rather than treating every megawatt-hour as interchangeable.

“We know clean air is valuable to people. We know that the environment is valuable to people” says Kaffine, “But there’s no market for it, so we don’t have a price for it. How do you put a number on that?”. Kaffine sees the work as ultimately in service of a simple goal. “At RASEI, the end game is always a better environment” he says “All the technical research is in service of making a cleaner environment. It is really cool to be able to trace these advances all the way through to the end impact.”

JULY 2026

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RASEI Welcomes Cheng Wang: Building Smarter, Leaner Hardware for the AI Era

Daniel Morton — Thu, 23 Jul 2026 18:23:13 +0000

RASEI Welcomes Cheng Wang: Building Smarter, Leaner Hardware for the AI Era Daniel Morton Thu, 07/23/2026 - 12:23

Daniel Morton

New Assistant Professor brings expertise in energy-efficient computing to RASEI’s research community

RASEI is pleased to welcome Cheng Wang as an incoming Assistant Professor, who will also be in the Department of Electrical, Computer, and Energy Engineering (ECEE) at CU �ֲ��ý. Wang is internationally recognized for developing innovative computing hardware that dramatically reduces the energy required for artificial intelligence and other data-intensive applications.

As the increase in AI use drives rapid growth in data centers, much of the conversation has focused on providing electricity and cooling. Wang’s research tackles the challenge from a different direction: making the computers themselves fundamentally more energy efficient through new hardware architectures inspired by the human brain.

Wang joins CU �ֲ��ý from Iowa State University, where he has spent the last four years building a multidisciplinary research group. Wang brings with him experience that spans both academia and industry, including time as a lead research scientist at Purdue University’s Center for Brain-Inspired Computing and as an R&D Engineer at Seagate Technology. Cheng earned a B.S. in Physics from Peking University and his Ph.D. from the University of Texas at Austin. The work produced by the Wang Group has already received wide recognition, with the funding of an NSF CAREER Award and multiple best paper honors. We’re excited to welcome him, and his research group, into the RASEI community.

Most current computer chips spend as much energy moving data between where the data is stored (the memory) and where the computation is done (the processor) as they do actually processing it. This is a decade-old inefficiency often called the “memory bottleneck”. It is like designing a kitchen where the pantry is on the opposite side of the building to where the stove is. Every time the cook needs an ingredient they must run across the building to grab it. Wang’s research asks what would happen if the chip could compute in the same location as where the data is already stored? The Wang Group designs “in-memory computing”, systems that do exactly that, along with the specialized designs of circuits and architectures that efficiently connect individual computing cores into a scalable system. By removing the need to shuttle data back and forth, significant energy reductions are possible in every single computation.

Another energy-saving approach the Wang Group are exploring begins by asking a more fundamental question: Instead of ‘forcing’ brain-like computing onto current designs of silicon chips, which were never designed for that kind of processing, how much performance and efficiency gains would we get by using hardware that was designed to behave more like a biological brain? The Wang group builds circuits made from nano-electronic and nano-magnetic materials, to behaviorally emulate how biological neurons fire and how synapses strengthen or weaken. Instead of having the typical digital “on/off” states, a more analog “gradient” of states is possible. These approaches have the promise to not simply drive down the energy required for computing, but also open up new approaches and opportunities for alternative modes of computation.

Wang’s research sits at the intersection of computing and energy efficiency, at a time when this is front and center for many communities. As artificial intelligence is being woven into much of today’s business and communication, the electricity demands of the data centers running it are of increasing concern; a core element of RASEI’s mission. Wang’s work on ultra-efficient, brain-inspired hardware offers a path toward a more efficient AI system. We are looking forward to the connections, ideas, and directions the Wang Group will bring to the RASEI research community.

Cheng explains that there were multiple draws that brought his team to the RASEI community. “I am excited to explore collaborations across the full stack of designing new devices and architectures”, said Wang. The expertise in materials science and device design present in the RASEI community, across CU �ֲ��ý and NLR, are natural partners to the research being done in the Wang group. “I can see many ways in which our research can develop to engage different aspects of the RASEI community” commented Wang. Of particular interest is the opportunity to engage with a new testbed being built at NLR for high-performance computing, specifically focused on optimizing energy efficiency. Cheng and his family are excited to be moving to the mountains, “When possible, I have biked everywhere since the sixth grade, so we are looking forward to exploring the bike paths across the area”.

Seth Marder, Director of RASEI, welcomes Cheng Wang to the community. He says that “Cheng’s research adds a new dimension to RASEI. As AI and data centers grow, much effort focuses on efficient delivery of power and cooling. However, reducing computing energy consumption is equally important. Cheng pioneers innovative approaches to improve computing hardware efficiency. I’m excited to see his impact and believe he’ll help RASEI advance energy-efficient AI and data center technologies”.

Bri-Mathias Hodge, Interim Department Chair of ECEE, highlighted the departments enthusiasm for the addition of Cheng Wang, adding: “We are excited to partner with RASEI to bring another great faculty member to campus. Cheng’s research is an exciting addition to the department, helping us bridge multiple areas of research strength.”

Please join us in welcoming Cheng Wang to RASEI. Take the opportunity to introduce yourself to him and his team.

JULY 2026

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The Hidden Chemistry Inside Tomorrow’s Solar Cells

Daniel Morton — Thu, 23 Jul 2026 16:06:02 +0000

The Hidden Chemistry Inside Tomorrow’s Solar Cells Daniel Morton Thu, 07/23/2026 - 10:06

Daniel Morton

Researchers uncover why perovskite solar cells degrade under reverse bias, opening new pathways to longer-lasting solar technologies.

Researchers just figured out why perovskite solar cells break down surprisingly easily under partial shading, and how to stop it. Perovskite solar cells are among the most promising candidates for the next generation of solar technology. They can convert sunlight into electricity with remarkable efficiency while offering the potential for lower manufacturing costs than today’s silicon-based panels. Before they can be scaled and deployed, there are some critical challenges to be solved, including ensuring the cells remain stable for decades under real-world conditions. A central question has been what happens when a perovskite solar panel is pushed into an unusual electrical state known as reverse bias.

Like all solar panels, perovskite solar cells occasionally experience reverse bias, an unusual electrical condition that can occur when part of the solar panel is shaded while the rest is in full sunlight. It has long been known that reverse bias quickly damages perovskite devices, but the pieces were not all fitting together. Current flowing through the cell under reverse bias is at the heart of the problem, and there are two ways this can happen. The first is apparent if the materials have big defects, electrons bolt through those defects like lightning and fry the cell, an acute failure mechanism. The second mechanism happens even in cells where those large defects are avoided or covered up, current can flow by a process known as quantum tunneling; much like taking a short-cut through interfaces in the cell. This current flows everywhere and while it is less abrupt than electrons flowing through defects, it will cause degradation in the cell over time. This gradual problem is much harder to understand because seeing these subtler processes in the cell is not easy. Existing theories explained parts of the problem, but they couldn’t fully account for how quickly some cells degraded or why certain device architectures proved far more resilient than others. Something important was happening inside the device that researchers couldn’t yet see.

Late last year, in October of 2025, a report led by RASEI Fellow Michael McGehee, a Professor at the �ֲ��ý, in collaboration with researchers at the National Laboratory of the Rockies (NLR; then named NREL), that explored the underlying mechanisms of the abrupt failure mechanisms of perovskite films under reverse-bias was published in Joule. The team identified that the defects were the sites of failure and demonstrated how to create films without defects that were much more robust to exposure to reverse bias.

To explore and better understand the gradual mechanism for degradation Michael McGehee assembled a new team of collaborators with the required expertise, including the groups of Edward Sargent from Northwestern University, Neal Armstrong at the University of Arizona, David Ginger at the University of Washington, and Joey Luther another RASEI Fellow at NLR. Together they combined advanced time-resolved electrical measurements, device modeling and materials characterization to watch how perovskite solar cells responded under reverse bias conditions, just published in Joule. Rather than just observing the damage, they set out to answer the key question of what hidden process was driving it?

The layers inside a solar cell create an energy landscape that electrons must navigate to get through the cell. By design, the interfaces act as energy “mountains” separating two valleys where electrons can be. Under reverse bias, ideally electrons cannot get over (or through) the mountain; the mountain is wide enough to keep electrons where they belong, and no current flows. Using these advanced measurement techniques, the team, led by Kell Fremouw (a Graduate Student in the McGehee group) and Ryan DeCrescent (a Research Associate with the McGehee group) was able to investigate the current-flow and degradation mechanism in remarkable detail. They were able to uncover a hidden process that had largely escaped attention: Under reverse bias, electrochemical reactions inside the solar cell weren’t just moving charged particles around as previously thought, they were actually creating new mobile ions. As these newly created ions redistribute and accumulate near interfaces, they gradually reshape the energy mountain, making it thinner until quantum tunneling becomes easy, and making it much easier for damaging current to pass through. Essentially the shifting chemistry was changing the device physics, providing important insights into why some device architectures show electrical breakdown and degrade much faster than existing models could explain.

These observations underlined an important perspective about these devices. Rather than simply behaving as electronic devices that move electrical charge, the cells also function as tiny chemical systems, with electrochemical reactions reshaping their internal structure under certain conditions. The initial device physics governs the ion creation, and the ion creation changes the device physics; this is an important feedback loop that can accelerate degradation. Identifying the hidden chemistry gives the researchers a much clearer picture of why the degradation occurs, and possible ways to prevent it.

Based on these findings, the team was able to identify where to intervene. The answer isn’t to try and repair the damage after it has begun, but to stop the chemical reactions from starting in the first place. By improving on the ultra-thin transport layers inside the device, the so-called hole transport layer (or HTL), the researchers showed that they could block the reactions responsible for creating new mobile ions. This solution is one that doesn’t require new equipment or exotic new materials, the team used standard materials and procedures but ensured that the layer placed in the device was very smooth, improving the coverage of the layer. With the electrical landscape preserved, the pathway to damaging currents remains closed, helping the cells maintain their performance for longer.

This new work, in combination with the study published last year, provides a holistic view of the two pathways that lead to perovskite decomposition under reverse bias. Importantly, both studies go beyond just observing the problem, they offer proven approaches to solve the abrupt and gradual degradation pathways. Preventing reverse bias degradation is a crucial component for the commercialization of perovskite solar cells.

For devices that may one day be expected to operate for decades on rooftops and in solar farms around the world, understanding the failure points is as important as improving efficiency. Efficiency will often get the headlines, but durability and resilience will decide whether perovskites make it onto a rooftop. This work doesn’t just observe and explain a failure mode, it provides a solution for one of the major challenges to scaling this new technology.

JULY 2027

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A New Dial for Controlling Light-Driven Chemistry

Daniel Morton — Tue, 21 Jul 2026 17:45:04 +0000

A New Dial for Controlling Light-Driven Chemistry Daniel Morton Tue, 07/21/2026 - 11:45

Daniel Morton

RASEI Fellow Niels Damrauer (�ֲ��ý) and a multidisciplinary team initiated by Professor Zach Wickens at the University of Wisconsin Madison just found a new way to control which molecules react in light-driven chemistry. The key to unlocking this new pathway? Focus on what happens after the reaction starts, not before.

SET: A powerful reaction for building organic molecules, such as medicines and materials

This type of reaction, called single electron transfer (SET), is one of the most useful tools in modern chemistry. It can be initiated by swapping in light or electricity instead of heat, making it more energy efficient and less prone to generating waste products. But there have always been some limitations with SET. Some molecules just don’t want to accept an electron, particularly when there are other types of molecules nearby that do the reaction faster, meaning that they’ve been locked out of this chemistry, until now. The new study, published in Nature with collaborators Zachary Wickens from the University of Wisconsin-Madison and Robert Paton at Colorado State University, opens the door to reactions that were previously impossible.

How Single Electron Transfer Works

One molecule, commonly after absorbing light, transfers an electron to another, triggering a reaction. Researchers have previously controlled the outcome of the reaction by picking molecules based on how ‘eager’ they are to grab, or accept, that electron. The molecule most ready to accept the electron wins. This approach has produced a wide range of really impressive chemistry, but it leaves out any molecule that isn’t ‘interested’ in the electron to begin with.

Identifying an opportunity

Every SET reaction actually has two steps, not one. First, an electron is transferred from a donor molecule to an acceptor molecule. Then, it has an option, it can either go forward to trigger a reaction, or it can go backward, undoing the first step. It is reversible. Chemists have always focused on controlling the first electron transfer. This team asked what would happen if they found a way to control the second electron transfer instead.

An extreme electron donor

To test this idea the researchers built what they call a “super-potent photoreductant”. It’s a light-activated catalyst that hands out electrons to almost every nearby molecule, good at accepting or not. In this particular research, the reductant is a solvated electron released from a photoexcited catalyst. Damrauer and his student Arindam Sau used time resolved spectroscopies to disentangle mechanism and identify conditions, such as the wavelength for photoexcitation, where catalysts could function. Damrauer notes, “By analyzing time-resolved signals in our experiment, my student Arindam was able to find colors for photoexcitation where the electron, the reductant, would be released deeper into the solvent, thereby affording it time to do its work in reducing the substrate molecules in solution.” But shouldn’t this reducing potency wipe out selectivity entirely? If every molecule gets an electron, which one ‘wins’?

RASEI Fellow Niels Damrauer at the graduation of one of the lead researchers Arindam Sau (�ֲ��ý, CO, 2026).

Reversibility is the key

The opportunity comes down to the second electron transfer. If a molecule accepts an electron, but doesn’t react quickly, the electron slips back to the catalyst and molecule floats away unchanged. If the molecule does react quickly, in a non-reversible way, the electron doesn’t go back to the catalyst and the reaction moves forward. Selectivity now depends on how reversible the electron transfer is, not how easy the initial electron transfer was.

Building a model reaction to test the hypothesis

The team tested this using a mixture of two molecules side by side: One that accepts electrons readily, but also gives them back easily, and one that ‘reluctantly’ accepts electrons, but then holds on tight once it does through a structural change. Under the old rules, the ‘eager’ electron acceptor would win. Under the new rules the ‘reluctant’ one wins, moving forward along the reaction pathway, leading to the formation of a new product that would not have been otherwise possible. Through a series of experimental explorative and optimization reactions the team were able to confirm that this selectivity preference held across a broad range of related molecules, not just the one test case.

No molecules left behind

With this works chemists now have a new dial to turn. Molecules that were previously incompatible with this efficient, light-driven chemistry are now available. This opens new pathways for building medicines and advanced materials, using less energy and creating less waste along the way.

JULY 2026

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Cutting Building Energy Use by a Third, One Neighborhood at a Time

Daniel Morton — Sun, 28 Jun 2026 18:29:56 +0000

Cutting Building Energy Use by a Third, One Neighborhood at a Time Daniel Morton Sun, 06/28/2026 - 12:29

Daniel Morton

What if the buildings in a neighborhood could share their heat the way a carpool shares a ride, essentially dropping off what one doesn't need right where another can use it?

That's the idea behind a Thermal Microgrid, and it's the subject of a recent paper that has won the ASHRAE Best Paper Award at the 2026 Annual Conference. The paper, "From Theory to Practice: Feasibility Study of a Thermal Microgrid at a US DoD Installation," was led by RASEI Fellow Gregor Henze in collaboration with researchers at the National Laboratory of the Rockies and the US Army Corps of Engineers Construction Engineering Research Laboratory. It was presented at the ASHRAE Annual Meeting in Atlanta in September 2025.

How it works

A Thermal Microgrid is, at its core, a network of pipes carrying water at near-ambient temperature between buildings. Instead of every building running its own heating and cooling systems in isolation, each connected building gets a compact, efficient water-source heat pump in place of conventional HVAC equipment. A building that needs to shed heat, such as like a gym, a data center, or a kitchen, can pass that heat directly to a neighboring building that needs it, rather than rejecting it to the outside air and then burning more energy somewhere else to make heat from scratch.

The result, according to the study: a 31% reduction in source energy use, roughly a third less energy consumed to heat and cool the same set of buildings.

Why a military base, and why it matters beyond one

The study specifically models feasibility at a US Department of Defense installation. Military bases are effectively self-contained microgrids already, with their own generation, distribution, and a mandate for energy resilience and security that goes beyond simple cost savings. Demonstrating a Thermal Microgrid on a base means proving it somewhere the stakes for reliability are highest, and where the case for reducing energy demand ties directly to operational security, not just utility bills.

The implications reach well past DoD. The same logic applies to any dense cluster of buildings with mismatched heating and cooling needs, such as university campuses, hospital complexes, and commercial building districts.

The data center connection

A current application of this concept is with data centers, which are drawing an increasing share of national attention, and national grid capacity, for their energy demand. Data centers generate enormous, near-constant waste heat as a byproduct of computing. Rather than treating that heat purely as a cooling problem to be discarded, a Thermal Microgrid offers a way to treat it as a resource: piping it to nearby buildings that need warmth, and cutting the total energy draw of the district as a whole. As data center construction increases, pairing new facilities with thermal-sharing infrastructure could turn one of the grid's fastest-growing loads into a source of heating for its neighbors.

Why now?

This year's record-breaking summer temperatures have pushed cooling demand, and grid strain, to new highs in many parts of the country. A 31% reduction in source energy use at the building-district scale is exactly the kind of solution that eases pressure on the grid during peak demand, while lowering costs for the buildings involved.

Congratulations to the whole team on this recognition!

JUNE 2026

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CHOISE Scientific Collaboration Awarded the 2026 Royal Society of Chemistry Faraday Horizon Prize

Daniel Morton — Wed, 24 Jun 2026 00:41:23 +0000

CHOISE Scientific Collaboration Awarded the 2026 Royal Society of Chemistry Faraday Horizon Prize Daniel Morton Tue, 06/23/2026 - 18:41

Daniel Morton

The Center for Hybrid Organic-Inorganic Semiconductors for Energy (CHOISE) has been awarded the 2026 Royal Society of Chemistry (RSC) Faraday Horizon Prize, in recognition of its creation of a new class of chiral semiconductors that unify the control of spin, charge, and light within a single electronically active material platform.

CHOISE is a Department of Energy-funded Energy Frontier Research Center (EFRC) bringing together 17 research groups from nine institutions: the National Laboratory of the Rockies (NLR), Duke University, the �ֲ��ý, the University of North Carolina at Chapel Hill, North Carolina State University, San Diego State University, the University of Toledo, the University of Utah, and the University of California Santa Cruz. The Center includes seven RASEI Fellows, and is led by Fellow Matt Beard of NLR.

RASEI Fellows Kirstin Alberi (NLR), Steve Barlow (CU �ֲ��ý), Joseph Berry (NLR), Jeff Blackburn (NLR), Joseph Luther (NLR), and Seth Marder (CU �ֲ��ý) are all part of the collaboration.

The RSC Faraday Horizon Prize is awarded annually in recognition of significant recent discoveries and advances in physical chemistry. In selecting CHOISE, the prize committee highlighted both the scientific excellence and the collaborative character of the work, recognizing how the team has come together across disciplines and institutions to develop innovative ideas.

At the heart of CHOISE's prize-winning research is chirality, the property by which molecules exist in distinct left- and right-handed forms. By embedding chirality directly into a semiconductor, the team has demonstrated that molecular handedness can govern the behavior of charge carriers and their spin. This establishes a fundamentally new paradigm for spin-dependent optoelectronics: technologies that use both light and electrical signals to process and transmit information.

Optoelectronic devices already underpin much of modern life, from the fiber-optic networks that carry global internet traffic, to the sensors in medical imaging, and the LEDs and lasers in everyday electronics. However, the next generation of technologies, including applications such as quantum computing, ultra-secure communications, and energy-efficient data processing, will demand far greater control over the quantum properties of electrons, particularly their spin. Conventional semiconductors offer limited means to achieve this. This is where this work comes in. CHOISE's chiral semiconductor platform opens a new route to that control, using the inherent geometry of molecules rather than complex external hardware to influence the properties of the signal. This could ultimately lead to devices that are not only more powerful, but significantly more energy-efficient.

JUNE 2026

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To capture carbon from the environment, we need to first decarbonize the grid

Daniel Morton — Thu, 14 May 2026 16:50:20 +0000

To capture carbon from the environment, we need to first decarbonize the grid Daniel Morton Thu, 05/14/2026 - 10:50

Daniel Morton

Most carbon capture research focuses on the chemistry. A new study from CU �ֲ��ý takes a big-picture look and asks hard questions about the whole system: what does it cost, at scale, and under real-world conditions?

Check out the Article

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In 2024, global average temperatures exceeded 1.5 ^oC above pre-industrial levels for the first time. This threshold was set as an aspirational limit by the 2015 Paris Agreement and was considered a line beyond which the impacts of climate change on ecosystem and human vulnerability become stark. Crossing this threshold is a signal that reducing emissions alone will not be enough. Increasingly, scientists, engineers, and policymakers around the globe agree that we will need to actively pull carbon dioxide (CO₂) out of the atmosphere to help reduce the impacts of this pollutant. The scale of this task is vast. The International Energy Agency projections suggest that reaching net-zero emissions by 2050 will require removing around one billion tonnes of CO₂ from the atmosphere every year. A billion tonnes of CO₂ is roughly equivalent to the annual CO₂ output of the entire global aviation industry. This vast amount needs to not only be offset from the system but fully removed from it.

This is the problem that has inspired a collaborative team of researchers at RASEI, including RASEI Fellows Prof. Wilson Smith and Prof. Bri-Mathias Hodge, and is the subject of a recent collaborative report published in Joule.

Two ways to catch carbon

Researchers are exploring a number of ways to pull CO₂ directly from the environment, and this comparative study looks at two of them side-by-side. The first, direct air capture (DAC), draws air from the atmosphere through a liquid solution that absorbs CO₂, analogous to a large-scale filter. It is the more established of the two approaches, with the world’s largest DAC facility currently under construction, a plant in Texas designed to remove 500,000 tonnes of CO₂ per year. The second approach examined in this study, direct ocean capture (DOC), is less developed but works with a natural advantage: it is estimated that the oceans absorb around 30% of the CO₂ that human activity produces each year, meaning seawater is already rich in dissolved carbon that originated in the atmosphere. By extracting that carbon directly from seawater, DOC bypasses the need to process enormous volumes of air. In fact, this advantage is one of the main reasons why many researchers are evaluating the feasibility of DOC as a CO₂ removal solution.

Both approaches share a common challenge: once you have captured the CO₂ from air, you need to do something with it. The regeneration process releases concentrated CO₂ in a usable form, while also recovering the capture solvent. In most current DAC systems, this process requires heating the captured material up to around 900 ^oC, typically by burning natural gas. This process is energy-intensive and creates its own greenhouse gas emissions, somewhat undermining the overall carbon capture process.

To try and understand the impacts of this overall process, the RASEI team modeled what happens when you substitute the heat-based regeneration setup with an electricity-driven alternative called bipolar membrane electrodialysis, or BPMED. Instead of using heat to release the CO₂, BPMED uses electricity to shift the chemistry of the captured solution, enabling the release of CO₂ at ambient temperatures. The key question the team sought to answer was whether this substitution makes economic sense when integrated with DAC and DOC, and under what kinds of conditions.

Building the model

To assess the DAC and DOC pathways, the team built a portfolio of connected models, starting from the physics of how CO₂ is captured and released, moving through the energy demands of each step, all the way up to a full cost analysis. This kind of approach, known as a techno-economic analysis (TEA for short), links the technical performance of a process directly to its economics. A TEA allows you to not just explore whether something works but also gain insight into whether it is viable at scale and under real-world conditions.

A particular strength of this study is the level at which the models connect these dots. As lead author Dr. Hussain Almajed (who started an ORISE Postdoctoral fellowship at the National Energy Technology Laboratory in July of 2025 shortly after graduating with his PhD from CU �ֲ��ý) puts it, the goal was to compare the two approaches “not to say which one is the winner, which one is the loser, but to highlight the trade-offs.” The team pulled data from the California electricity grid, modeled different power supply scenarios, and ran both the DAC-BPMED and DOC-BPMED systems through the same framework. This provided a side-by-side comparison, one that had not previously been explored, that produced some unanticipated observations.

Two technologies, two cost profiles

The comparative study revealed a foundational trade-off rooted in a fundamental difference between DAC and DOC: Concentration. Air contains about 120 times less carbon than seawater, requiring large volumes of air to be processed at every iteration. However, once the CO₂ is captured via a liquid solvent, typically a hydroxide, the comparison reverses. A typical liter of DAC solution contains 0.5 to 1.0 moles of dissolved carbon, which is roughly 160 to 320 times higher than the dissolved carbon in a liter of seawater. That means a DAC plant needs to process far less liquid to recover a given amount of CO₂ compared to DOC, but extracting carbon from such a concentrated solution requires running the BPMED part of the system at high intensity, at high electrical current, which consumes significant energy. The equipment footprint is relatively small, but the electricity bill is high.

DOC works the other way around. Because seawater holds less dissolved carbon compared to a DAC solution, a DOC plant must process vast amounts of seawater to recover the same amount of CO₂. The models estimate that DOC-BPMED would need roughly 20 times more membrane area than the equivalent DAC-BPMED system, representing a significant upfront investment. On the other hand, the electrically driven process can run at a much lower current when handling dilute seawater, using considerably less energy per tonne of CO₂ captured.

These differences are obvious in the cost estimates. For a plant capturing 100,000 tonnes of CO₂ per year, and connected to the current California electricity grid, the modeled cost of capture via DAC-BPMED came in at around $470 per tonne of CO₂ in the baseline case. For DOC-BPMED, the equivalent figure was around $1,500 per tonne, roughly three times higher. This is driven largely by the upfront cost of all the additional equipment, and not the energy use.

The authors are careful to state that these modeled estimates have a meaningful level of uncertainty built in, and they will shift as the underlying technologies mature. But the overall trends are clear. At present, and with the current equipment costs, DAC-BPMED has a significant cost advantage over DOC-BPMED under this electrically driven regeneration approach.

Unexpected potential routes to profitability

A finding that stood out from these models was an often overlooked commodity side product. The BPMED process works by using electricity to split a salt solution into an acidic stream, which is used to release CO₂, and a basic stream which produces sodium hydroxide (NaOH). Sodium hydroxide is a widely used industrial chemical, a commodity found in a range of industries such as paper manufacturing, water treatment, and chemical synthesis, with an established market value, averaged at around $450 per tonne.

In the DOC model, because the plant is processing such large volumes of seawater, it produces considerably more sodium hydroxide than it needs for its operation. The models show that selling that surplus could reduce the cost of the overall CO₂ capture process substantially. In a scenario projecting a largely decarbonized electricity grid by 2050, the revenue generated from sodium hydroxide sales was enough to fully offset the costs of the CO₂ capture process, and in the most optimistic scenario, the process showed a net profit.

The authors were candid about the limits of this finding. The global sodium hydroxide market, even accounting for projected growth, is not large enough to absorb the products from carbon capture at the scale required to make a meaningful dent in atmospheric CO₂ “Our brief market analysis showed that even if DOC-BPMED supplied 20% of the projected 2050 sodium hydroxide demand, it would still offset less than 0.1% of today’s global energy emissions.” Dr. Almajed said. But the principle illustrated by this finding has broader implications. Coupling carbon capture with the production of a valuable commodity, either carbon-based, or as a side-product, could be a viable route to improving the economics of the whole process. It is an approach that is already being pursued commercially, including by Travertine Tech, a company based in �ֲ��ý, Colorado, which captures CO₂ while producing and selling phosphoric acid, gypsum, and cementitious materials.

The electricity issue

Because the BPMED regeneration process is driven entirely by electricity, the source of that electricity matters enormously. This impacts both the cost of the process, and whether it actually delivers a net reduction in atmospheric CO₂. A carbon capture plant powered by fossil-fuel generated electricity that itself emits CO₂ is self-defeating.

To explore how different electricity generation modes impact the overall process, the team modeled four power supply scenarios. The current California grid, a projected 2050 California grid operating at 95% decarbonization, and two off-grid options: dedicated wind and dedicated solar. Interestingly, the team found that connecting to the grid outperformed both off-grid renewable options on cost, in both the current and the projected scenarios. The authors suggest that in the model this is down to a matter of reliability, a grid-connected plant can essentially run continuously, spreading its capital costs across more operating hours. A plant running on dedicated solar or wind is constrained by intermittency, which can drive up the cost per tonne of CO₂ captured. Dr. Almajed highlights that this is an area of the model that could be expanded, “We just looked at solar or wind each by itself, we didn’t optimize the off-grid scenarios to include energy storage and batteries.”

The policy implication built from the observations across the model is clear, explains Dr. Almajed, “We need to really pursue grid decarbonization. We need cleaner energy to power technologies that are going to help address climate change.” Technologies, such as DAC- and DOC-BPMED do not operate in isolation from the broader energy system. The effectiveness of these technologies to help combat atmospheric pollution, both economically and technically, is critically dependent on the grid they are plugged into. Decarbonizing that grid is not a separate problem, it is a prerequisite.

The future of carbon capture

While there are a lot of valuable observations and ideas that have come out of this TEA, no model is perfect. The team was quick to clarify areas where their model could be refined as technologies and ideas evolve. “When technologies are in such a nascent stage, the analysis of these models should focus on qualitative, rather than quantitative, insights” explains Prof. Bri-Mathias Hodge. “While there are a number of areas where the model can be improved, it also suggests where efforts for improvements are best focused, particularly the aspect that have the largest impact on results.” This includes more detailed modeling of the membranes, better data on equipment costs as the technology matures and is more widely deployed, and a more complete optimization of how these carbon capture plants might interact with energy storage or hybrid power systems. Many of these are manageable problems, and work is already underway at RASEI to address some of these areas.

Sometimes, the real value in this kind of analysis is in what it reveals before such refinements are made. By mapping the full system, from the technical fundamentals through the macroscale economics, this study helps to identify where research effort is best directed. Enhancing the concentration of the dissolved carbon in the seawater fed into a DOC plant, for example, could reduce costs by 40-50% according to the study’s sensitivity analysis. As a technology that is beginning to be deployed and scaled, identifying areas where large improvements in process efficiency can be made could have significant energy, and cost savings. As Dr. Almajed notes, “The study generated a lot of insights that we didn’t even consider at the start of the project.”

Removing carbon from the atmosphere at the scale required to significantly impact global emissions is an interdisciplinary problem that spans chemistry, engineering, economics, and energy policy. Analyses such as this don’t necessarily resolve that complexity, but they do help to make it understandable, and act as a roadmap to focus efforts. Knowing where the bottlenecks are, and insights into what it would take to impact them, is a great way to start solving the problem.

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Watching Carbon Capture in Action

Daniel Morton — Wed, 13 May 2026 21:00:48 +0000

Watching Carbon Capture in Action Daniel Morton Wed, 05/13/2026 - 15:00

Daniel Morton

Removing carbon dioxide (CO₂) directly from the air, a process called direct air capture (or DAC), is one of several approaches being developed to help reduce the concentration of this greenhouse gas in the atmosphere.

Check out the Article

Elsewhere in the news

EurekAlert

Among the methods being scaled up, one of the more established involves exposing air to a strongly alkaline liquid, typically a solution of potassium hydroxide (KOH), commonly known as lye. The liquid chemically binds the CO₂, converting it into dissolved salts called carbonates and bicarbonates. Large facilities using this principle are already operating or under construction, with one plant in Texas that is currently under construction, designed to remove 500,000 tons of CO₂ per year.

Despite the maturity of the underlying chemistry, there has been a fundamental limitation in how well researchers can study it. Until now, the process has been something of a black box. Scientists could measure what went into a capture system and what came out, but the detailed chemistry happening inside, specifically in the thin zone where the air and liquid meet, was very difficult to observe directly. This is a meaningful gap, because what happens in that zone determines how efficiently the system works, and how it should be designed, especially for novel DAC liquids. As Jason Pfeilsticker (a Graduate Student in the group of RASEI Fellow Wilson Smith, and lead researcher on this project), explains, “This really is a case of if you want to know about something, just look at, really carefully, and in this case there was some work to do before we could take a detailed look”.

Think of it like medicine before medical imaging. For centuries, doctors understood that the body had internal structures and processes, but could only examine them indirectly, through symptoms, pulses, and what came out of the body. The development of X-rays and later MRI scanning did not change human biology, but it transformed what could be understood and acted upon. A diagnosis that once required guesswork could suddenly be made based on the information gained from mapping out the internal structures of the body. This study, just published in ACS Energy Letters, represents a similar shift for CO₂ capture: rather than inferring what is happening at the gas-liquid interface from indirect measurements, researchers in the group led by Wilson Smith at the �ֲ��ý have built an instrument that lets them watch it directly.

The instrument at the center of this work is a custom-designed laboratory flow cell. This device was designed and built specifically for this purpose and, to the teams’ knowledge, is the only one of its kind. “There were so many different variables that we wanted to explore, but in order to design a better process and or screen novel DAC solvents, we needed to have a better picture of what was going on” explains Pfeilsticker, “You can change the solvent, the pressures, the flow, the reactor design, all of which affect the microenvironment and thus the DAC performance ”. To get a clearer picture they set out to build a flow cell with built in features that enabled accurate spatial mapping of the kinetics of the reaction, in real time. Designing and building it required solving a series of practical problems. The cell needed to bring CO₂ gas into contact with flowing KOH liquid through a porous membrane, closely mimicking the interface in a real capture system. It needed to be optically clear and stable enough to allow laser-based measurements without bubbles, vibrations, or chemical interference disrupting the readings. The flow inside needed to be smooth and predictable, what scientists call laminar flow, so that the measurements could be interpreted meaningfully. Each of these requirements shaped the final design, from the choice of materials to the geometry of the flow channels. However, this oversimplifies the actual process, these lessons were learned as part of an extensive prototyping process.

“We made at least 60 or 70 iterations of this cell during the project” explains Jason. “I was drawn to this project because I really like to make things, and this looked like a challenge that would use a great combination of scientific investigation, detailed design and hands-on building”. Jason, who spends much of his free time working on motorcycles, or building electronics and musical instruments, knew he was going to need to iterate on the cell design. Early on the team considered getting design iterations professionally machined. But each of these would cost thousands of dollars to produce, and when you are learning what is important as you are designing, a small tweak here and there can become very expensive. A typical filament-based 3D printer would not be suitable for working with the chemicals involved in DAC. “We identified a resin that was chemically compatible with the base reagents we were using, and we found a cheap resin 3D printer online, that let us do some initial proof-of-principle work, then we upgraded to a better 3D printer for the project, and now we could print iterations for less than a dollar,” said Jason. This not only made the process cheaper but sped-up design development as well. The team identified three big challenges as they worked through the designs: good seals, bubbles, and smooth flow of the liquid. The solutions for these came from a number of inspirations, including sealing mechanisms borrowed from drumheads, reactor geometry angles to reduce bubble formation to enable effective laser probing, shaping of the flow inlets and outlets to ensure laminar flow, and flow dampener design.

Some of the prototype cell designs that were printed and tested during the iteration stages. Photo Courtesy of Jason Pfeilsticker, 2026.

To explore the reaction and map out the kinetics of the process the team used a technique called confocal Raman spectroscopy to make their measurements. This works by shining a laser at a point in the liquid and reading the light that scatters back; different chemical species produce distinct signatures, making it possible to identify and quantify them. By scanning the laser across the cell in a grid pattern while the process was running, the team built up two-dimensional chemical maps, essentially pictures showing where carbonates and bicarbonates were forming and accumulating across the contact zone, at the scale of fractions of a millimeter, in real time.

What those maps revealed was not what simple intuition would predict. “We saw that the equilibrium reaction is in effect going backwards near the surface” explained Pfeilsticker. When fresh KOH first contacts CO₂, the highly reactive hydroxide ions in the liquid rapidly consume the incoming CO₂, converting it to carbonate near the membrane. But this rapid reaction locally depletes the hydroxide supply right at the interface. As the liquid flows further through the channel and more CO₂ is absorbed, there are fewer hydroxide ions available near the membrane to drive the reaction forward. “Because it is laminar flow, there is no turbulent mixing” said Jason. The result is that a thin layer of bicarbonate, an intermediate chemical species in the conversion process, forms immediately next to the membrane, nestled between the membrane surface and the main hydroxide and carbonate-rich zone further into the liquid. This pattern becomes more pronounced further along the flow channel and represents a direct, spatial record of the chemistry unfolding in real time.

The team also found that operating conditions matter. Higher flow rates altered the shape and extent of the reactive zone, and doubling the concentration of KOH shifted the balance of products and appeared to reduce the hydroxide depletion effect near the membrane, potentially useful information for future system designs.

A key part of this work was the development of a computational model mirroring, and interpreting, what is going on inside the cell. Using the experimental observations to provide a framework to build the theoretical model allowed the team to effectively bound the scope and validate the model, in ways that would have been essentially impossible without the experimental data. The hope is that this model, which has now been validated with experimental data, in conjunction with flow cell maps can be used by future researchers as an initial screening tool in designing new DAC systems.

This work has the potential for significant impact. DAC Facilities using alkaline liquids are being built at the industrial scale. Researchers are actively developing new and improved capture liquids to make the process more efficient, cheaper, and use less energy. With a cell design that enables accurate mapping, and a computational model that enables faster screening, the process of optimizing the carbon capture reactions can be accelerated. On an industrial scale even small improvements in reaction efficiency and cost can have huge savings on the system scale. Current approaches just look at the input and corresponding output of the cell, like judging a medical treatment by whether the patient recovered, without being able to examine what really happened inside the body.

This research describes a detailed, data-driven approach to answering the questions about what is really happening at the reactive center of DAC: how does a given liquid behave, what is happening at the interface where the chemistry is happening, how does varying the conditions impact the reaction? The combination of the experimental and theoretical tools disclosed by this work provides insight into how these processes work, and the key variables that can be used to optimize it.

The application of these tools can potentially extend beyond DAC. Wherever chemistry and transport interact at an interface, such as electrochemical systems that convert CO₂ into fuels or commodity chemicals, or in the separation of critical minerals. The design of this device was around one specific challenge, but has the potential for broad utility.

The transition from black box to observable system does not, by itself, solve the engineering challenges ahead. Models still need refinement, and scaling to industrial practice requires substantial research. But the ability to directly observe what is happening is a critical step in that process. What was previously assumed can now be tested. The reaction black box now has a window, that enables researchers to gain valuable insights into the inner workings of this critical process.

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The solar cell that moonlights as an LED, and does both better

Daniel Morton — Mon, 27 Apr 2026 22:30:02 +0000

The solar cell that moonlights as an LED, and does both better Daniel Morton Mon, 04/27/2026 - 16:30

Daniel Morton

Imagine a display that harvests ambient light when it is not actively in use, offsetting some of its own energy consumption. The materials physics shows that this is possible, the same semiconductor material can, in principle, emit and absorb light efficiently. What has been missing is a device architecture that allows it to do both without reductions in efficiency of either application. A new study reports a perovskite diode that converts sunlight to electricity at 26.7% efficiency (a world record at the time of publication submission) and emits light at 31% efficiency, figures that would be high for a device designed to do only one of those things.

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Read the Article here

EurekAlert!

The Brighter Side

Metal-halide perovskites are a class of materials named for their distinctive crystal structure, that have emerged over the past decade as some of the most promising candidates for next-generation solar cells and light-emitting diodes (LEDs). They are relatively inexpensive to produce, can be tuned to absorb or emit different wavelengths of light, and have shown efficiency levels that rival far more costly semiconductor materials. Yet despite sharing the same underlying material, perovskite solar cells and perovskite LEDs have largely been developed as separate technologies, because the physical requirements of each push device design in opposite directions. A collaborative study published in Joule by a team led by Michael McGehee at the �ֲ��ý, and Jixian Xu at the University of Science and Technology of China, now demonstrates that this conflict can be resolved, and that resolving it improves both devices at once.

The challenge of doing two things at once

The tension between perovskite LEDs and solar cells comes down to a question of thickness. An effective LED needs an extremely thin, discontinuous layer of perovskite, typically around 50 nanometers (roughly one thousandth the width of a human hair), because thin, slightly uneven films naturally scatter light outward, helping photons escape the device. A solar cell, by contrast, needs a layer roughly sixteen times thicker to absorb enough incoming sunlight and convert it into electricity efficiently. For years, this meant that researchers optimizing a perovskite LED were building something poorly suited to harvesting solar energy, and vice versa. Thanks to these different needs the two applications have followed separate architectural paths, and devices that attempted to do both tended to do neither particularly well.

There is a further complication. Even in a well-made perovskite LED device, much of the light generated inside never escapes. When a photon (a particle of light) is produced inside the material, it travels outward and hits the surface. If it arrives at too steep an angle, it is reflected back inside rather than escaping, a phenomenon governed by the physics of how light moves between materials with different optical properties. Once trapped, that photon bounces around until it is absorbed by a microscopic defect in the material and converted to heat, essentially wasted energy. Reducing these losses requires both giving trapped photons a better route out and patching the defects that absorb them along the way. These have typically been treated as separate engineering problems.

A useful way to think about what the team describe in this research is to consider what a texture does to a pane of glass. Smooth, flat glass transmits light reasonably well in one direction, but offers little control over what happens to light approaching from awkward angles. Some passes through, some reflects, and the behavior is largely determined by the geometry. A textured or patterned surface changes this: by introducing deliberate variations in the surface structure, light arriving from many different angles can be redirected more usefully, whether that means bending it inward toward an internal target (for a solar cell) or redirecting it outward toward an observer (for an LED). The same surface feature serves both directions of travel. The team's approach works on a closely related principle, applied to structures far smaller than any surface texture visible to the naked eye, and with the added benefit that the material forming those structures also repairs the defects that were previously wasting energy as heat.

Building porous textured sponges

Building on earlier collaborative work published in Science in 2023, by McGehee and Xu, which demonstrated that porous alumina nanoplates (a form of aluminum oxide) could reduce energy losses at perovskite interfaces, the team set out to extend that principle into a more sophisticated architecture. The key advance was developing a method to assemble alumina nanoparticles into micrometer-sized islands (each around five micrometers across and half a micrometer tall) embedded within the perovskite device. The assembly process uses electrostatic attraction: two populations of alumina nanoparticles are given opposite surface charges, and when mixed, they cluster together naturally into porous, sponge-like islands. One population is treated with a negatively charged molecule (Me-4PACz) and the other population treated with a positively charged molecule (ODA). The team refer to these as e-Al₂O₃, where the "e" denotes “electrostatic” assembly.

The porous sponge-like structure is critical. Earlier approaches to introducing low-refractive-index materials (materials that are less optically dense than the surrounding perovskite) into LED devices tended to block the flow of electrical charge, undermining device performance. Because the e-Al₂O₃ islands are porous, the perovskite material can grow through them, maintaining electrical contact with the electrode beneath. The islands therefore redirect light without interrupting the charge transport the device depends on.

The surface treatments applied to the alumina nanoparticles were designed to serve a second, equally important function. The molecules used to give the particles their opposite charges are the same molecules known to passivate perovskite surfaces, essentially chemically neutralizing the defects where energy can be lost as heat. The surface recombination velocity, a measure of how quickly electrical charges are lost at interfaces, dropped from 20.2 cm/s in a flat control device to 1.4 cm/s in the e-Al₂O₃ device. This brings the rate of energy loss at the interface close to levels seen in high-performance silicon solar cells.

With defect losses suppressed to this degree, a useful secondary effect called photon recycling becomes significant. When a photon is generated inside the perovskite and would otherwise be trapped and lost, it now has a reasonable chance of being reabsorbed by the material and re-emitted, effectively getting a second, or third, attempt to find an exit. This would be counterproductive in a defect-rich material, because each reabsorption event would risk the photon being lost to heat. However, with defects minimized, photon recycling amplifies the benefit of the improved light routing, pushing external efficiency higher than the geometry of the device alone would predict.

Operated as a solar cell, the e-Al₂O₃ device achieved an externally certified stabilized power-conversion efficiency of 26.7%. At the time this work was submitted for publication this cell held the world record for the power conversion efficiency for perovskite devices (held between 05/2024 – 02/2025). Operated as an LED with the same 800 nm thick perovskite layer, the device reached an external quantum efficiency of approximately 31%, meaning roughly 31 out of every 100 injected electrons produced a photon that successfully escaped the device. Radiance (a measure of light output intensity) was nearly ten times higher than the flat control device. Across both operating modes, the e-Al₂O₃ devices also showed meaningfully improved long-term stability, retaining 95% of their initial solar cell efficiency after 1,200 hours of continuous operation, compared with 67% for the flat control.

The authors note that this combination of greater than 26% solar cell efficiency and greater than 30% LED efficiency in a single polycrystalline device is, across all photovoltaic materials, only the second time this has been demonstrated, the first being single-crystal gallium arsenide, a material that is substantially more expensive and more difficult to manufacture at scale.

The practical implication of a device that converts sunlight to electricity efficiently and emits light efficiently is not merely academic. Displays that harvest ambient light to extend battery life, or lighting systems that recover energy when not actively in use, become more plausible when the same device architecture serves both functions without meaningful compromise in either. More fundamentally, the work demonstrates that the long-standing separation between emissive and photovoltaic device design is not a physical inevitability but an engineering problem, one that careful co-optimization of optical and electronic properties can address.

April 2026

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The Physics That Hides in Plain Sight

Daniel Morton — Wed, 22 Apr 2026 15:30:34 +0000

The Physics That Hides in Plain Sight Daniel Morton Wed, 04/22/2026 - 09:30

Daniel Morton

Just published; a Perspective article by RASEI theorists raises new questions on what is hidden by quantum symmetry

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Check out the Perspective Here

Some of the most interesting actions happening inside a material are the things that, according to the rulebook, shouldn't be happening at all. In the world of quantum physics, that rulebook is written by symmetry, as encoded by the geometric arrangement of atoms in quantum matter. Essentially, how the atoms are stacked together in a solid. Symmetry sets strict rules about what physical effects are, and are not permitted. For decades, when experiments on certain materials produced results that symmetry said were impossible, the standard assumption was that something had gone wrong: a flawed measurement, or a contaminated sample. A new framework published by the group of Alex Zunger in the journal Matter suggests that in many of those cases, nothing had gone wrong at all. The effects were real. Indeed, they were just hidden—permitted by the local symmetry rules operating in small regions, or neighborhoods, not by the material's overall structure. Understanding where and how these hidden effects occur has practical consequences: the behavior of electrons in magnetic materials underpins technologies from computer hard drives to medical sensors, and knowing the full picture of what electrons can do can save us from discarding potentially critical new materials with hidden technological virtues.

Spin, and why it matters

To understand what this framework is doing, it helps to start with spin itself. Spin is a quantum property of electrons, one that has no obvious everyday analogy, but which causes electrons to behave, in some respects, like tiny magnets with a fixed orientation. In most materials, the spins of individual electrons point in random up or down directions and cancel each other out. But in certain materials, and under certain conditions, spins can be organized spatially and can be controlled. Moreover, even when spins cancel each other out over the global volume of a sample, the local rules operating in smaller regions can have a different spin symmetry, controlling the properties of the sample as a whole.

These unusual spin behaviors control the foundation of a field called quantum spintronics. Spintronics is, broadly, the use of electron spin rather than just electron charge to store, process, and transmit information. The hard drives in most computers already exploit this principle: the read heads that detect stored data work by sensing differences in how electrons with different spin orientations pass through a material. Researchers are working towards spintronic devices that are faster, smaller, and more energy-efficient than what charge-based electronics alone can achieve.

The catch is that developing useful spin behavior out of a material requires the right conditions. This is where symmetry re-enters the picture. The chemical identity and spatial arrangement of atoms in a solid determine its overall properties. Change the atomic arrangement, and you change what spin can do. For this reason, identifying which materials have the right symmetry for a given spin effect has been central to the field. And for a long time, if a material's overall symmetry appeared to rule an effect out, that material was simply set aside.

Walking the streets: a new map of spin physics

The new framework addresses this directly. Rather than treating spin effects as simply present or absent in a given material, it draws a distinction between two types: apparent and hidden effects.

Apparent effects are those that follow directly from a material's overall atomic arrangement. If the global symmetry permits a spin effect, you expect to see it, and you do. Hidden effects are more subtle. They occur in materials where the overall atomic arrangement would, according to the current rulebook, forbid a given behavior, but where smaller, localized regions, or neighborhoods, within the material have their own legitimate symmetry that permits it. The global picture says no; the local picture says yes. The local picture wins. To comprehensively understand the potential spintronic virtues of a material, we need to also understand the mysteries of the local arrangements and symmetries of the spins.

A good way to think about this is to imagine judging a city's architecture and character purely from a satellite image. At that resolution, everything might look uniform and regular. Walk the streets, and observe the neighborhood at eye level, and an entirely different set of structures and interactions becomes visible. The framework outlined in this Perspective is insisting that materials physics needs to walk the streets, and that a great deal can be missed by staying at altitude.

To organize this, the framework described by the Zunger team sorts spin effects in magnetic and non-magnetic materials into distinct categories, determined by two key factors: whether the effect is apparent or hidden and whether the spin effect requires a help from a phenomenon called spin-orbit coupling (SOC)—an interaction emerging from relativistic theory of matter, in which an electron's motion through the electric field of an atomic nucleus influences its spin orientation. Some spin effects depend on this interaction; others do not, and this distinction has meaningful consequences for which materials can host them and how large the effects can be. Check out Box 1 for a deeper dive into these effects.

Box 1:

Apparent spin splitting induced in non-magnetic materials by relativistic SOC: The Rashba and Dresselhaus effect: Across all categories, the framework identifies both an apparent and a hidden version of each effect. The team helps provide understanding around this categorization by providing theoretical physics worked-out examples inspired by real, experimentally studied compounds. For example, in non-magnetic materials, well-known effects called the Rashba and Dresselhaus effects (both involving spin-orbit coupling) producing a separation of electron spin states, have previously overlooked hidden counterparts that can occur in materials whose overall symmetry would appear to rule them out. The framework points to the possibility that there can be materials that violate the nominal conditions for the (apparent) Rashba effect, but a hidden Rashba effect exists. For example, a hidden Rashba effect can show spin polarization even if the global symmetry violates the required broken inversion symmetry, but the structure consists of sectors that are individually non-symmetric. Predicted materials with hidden Rashba spin polarization pointed out by the new framework include tetragonal BaNiS₂ and tetragonal LaOBiS₂, whereas materials with hidden Dresselhaus spin polarization proposed theoretically exhibits local spin texture (the pattern of spin orientations across the material), but no spin splitting include hexagonal NaCaBi, cubic Si, and cubic Ge. This new perspective legitimizes the search for such materials that violate the (apparent) Rashba conditions yet show a (hidden) Rashba effect.

What can be hidden in magnetic materials?

In magnetic materials, hidden spin effects can arise not from the relativistic effect of spin-orbit coupling, but from the magnetic interactions between atoms. This means they can, in principle, be larger, and occur in materials containing lighter, more abundant elements. In both cases, the street-level view of the material is revealing structures and interactions that the satellite image simply could not see. You can find out more about examples of an apparent and a hidden SOC-independent effect in Box 2.

Controlling the electronics of materials

The practical significance of the framework extends beyond classification. The Perspective article explores whether hidden and apparent spin effects can be actively controlled, and, in certain materials, the answer is yes. In some antiferromagnetic compounds, switching between hidden and apparent spin states can be achieved using an electric field. This would be enabled if one could design a material that, in addition to (either apparent or hidden) spin-split AFM symmetry can have the added symmetry of polarity (how electrons are arranged across atoms). This will allow potential applications of the ability to switch spin states using only an electric field.

This is notable for a few reasons. Antiferromagnets carry some practical advantages over the ferromagnets (materials like iron, where all magnetic moments point the same way), that currently dominant magnetic technology. They produce no stray magnetic field, which reduces interference with neighboring components, respond rapidly to switching signals, and are robust against external magnetic disturbances. The ability to toggle spin effects electrically in these materials adds a further tool for device designers to work with.

Box 2:

Apparent, SOC-independent spin splitting in antiferromagnetic materials: Spin configurations consisting of alternation of spin-up layer followed by a spin-down layer are called antiferromagnets. For a long while it was textbook knowledge that electronic states in antiferromagnets would have the same energies for spin-up and spin-down layers (a behavior called “spin degeneracy”) in the absence of SOC. This is because it was assumed that the two atoms with opposite spins will compensate each other, giving rise to spin degeneracy. In 2020, the Zunger group with Emmanuel Rashba discovered the enabling symmetry conditions for the unusual case where electronic states in an antiferromagnets would have different energies for different spin (“spin-split antiferromagnets”) in the absence of SOC. Since this behavior follows the precise symmetry of the system it constitutes an apparent effect. Theorists soon pointed to real materials that would have such peculiar effects, including orthorhombic LaMnO_3, rhombohedral MnTiO₃, tetragonal KRu₄O₈, and tetragonal V₂Te₂Oand many others. This effect was later dubbed in the literature “altermagnetism” implying another form of magnetism.

Hidden, SOC-independent spin polarization in antiferromagnetic materials: In collinear antiferromagnets (collinear, meaning the psins all point along the same axis), this requires that (i) global system symmetry forbids SOC-independent spin splitting, but the (ii) local sectors break that symmetry. Predicted hidden spin polarization materials in magnetic AFM include tetragonal Ca₂MnO₄, La₂NiO₄, and MnS₂, and the following tetragonal compounds CoSe₂O₅, Fe₂TeO₆, K₂CoP₂O₇, LiFePO_4, Sr₂IrO₄, and SrCo₂V₂O₈.

Finding real materials with previously unsuspected hidden effects

The question is how one can use theoretical physics to search for specific materials with target spintronic properties? The history of material research and condensed matter physics has often proceeded via accidental discovery of materials with interesting physical properties—superconductors and light-emitting semiconductor. Yet, for many applications we know well what type of physical properties we want, but we do not know a material that has those target properties. An interesting advance was worked out in the research group of Alex Zunger: namely “Inverse Design”, where you find a material that has a specific, desired target property. The obvious obstacle is that there are innumerably many possible atomic structures that could, in principle, be made even from a few elements and we do not know which structure would have the desired target property. It turns out that modern atomic-resolution quantum mechanics (i.e., electronic structure theory) can now be combined with biologically inspired (evolutionary) “Genetic Algorithms” to scan a truly astronomic number of atomic configurations in genomic-like search of the one(s) that have desired, target materials properties. Once the number of configurations with target property is narrowed down to a few, laboratory synthesis becomes viable. Examples of specific compounds, known to exist but not known to be spintronic relevant were predicted theoretically as a result of this work.

A broad implication of this new framework is that the rulebook has been applied too rigidly. By demonstrating that hidden effects are real and systematic rather than accidental, the framework significantly expands the pool of materials worth investigating for spintronic applications. Materials that were previously set aside because their overall symmetry appeared to rule out useful spin behavior may, on closer, street-level, inspection, host exactly the effects that researchers are looking for, just in a form that requires a more careful look to find.

The Perspective also flags a subtler problem. Some of the theoretical tools routinely used to model materials are themselves guilty of the same “farsightedness” that causes hidden effects to be missed. Certain widely used approximations work at too coarse a resolution to detect local symmetry and therefore fail to predict effects that are genuinely present. Refining the theoretical toolkit is, as the authors suggest, as important as expanding the materials search.

Taken together, this framework offers a more complete account of what electrons can do inside a solid, and one that takes local structure seriously rather than assuming the view from altitude tells the whole story. The physics was there all along. It just required a closer look to find it.

April 2026

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