At the heart of this limitation lies a subtle but pervasive problem: electronic disorder caused by environmental imperfections. Graphene’s ultra-thin nature makes it highly vulnerable to minute fluctuations generated by charged impurities embedded in surrounding materials. These charged defects induce spatial variations in charge density, which manifest as so-called electron-hole puddles. Such inhomogeneities scatter electrons, hindering their ability to travel freely and drastically limiting mobility. This challenge has stood as a formidable barrier in harnessing graphene’s full potential for quantum and electronic applications that demand ultra-clean conductive platforms.

A recent breakthrough, however, has uncovered innovative strategies that surmount this historic obstacle, propelling graphene beyond the performance of state-of-the-art GaAs semiconductors even at cryogenic temperatures. Two parallel studies, spearheaded by teams at the National University of Singapore (NUS) and The University of Manchester, reveal complementary approaches to drastically reduce electronic disorder, thus unlocking record electron mobilities and enabling the observation of quantum phenomena under unprecedentedly mild conditions. These findings signal a paradigm shift in quantum materials research and the engineering of next-generation electronic devices.

Assistant Professor Alexey Berdyugin, a leading figure in the NUS Department of Materials Science and Engineering and co-corresponding author of both studies, explains that electron mobility quantifies how easily charge carriers navigate a material when subjected to an electric field. Higher mobility implies faster, less resistive electron flow which is essential for realizing ultra-fast, energy-efficient electronics. Specifically, materials exhibiting exceptionally high mobility are poised to transform advanced computing, sensing technologies, and emergent quantum platforms where coherent control of electrons is critical.

In the first pioneering study, researchers focused on inventing a method to protect graphene from the disruptive charge impurities prevalent in its environment by leveraging the concept of Coulomb screening. This involves strategically deploying additional graphene layers as ultra-thin electrostatic shields. By stacking two graphene sheets with a large twist angle relative to each other (between 10° and 30°), they ensured the layers remained electronically decoupled while still residing within a nanometer of each other. This unique geometric configuration allowed one graphene layer to be doped deliberately to behave like a metallic screen, effectively ironing out spatial charge fluctuations that scatter electrons in the primary graphene layer.

This twist-engineered Coulomb screening drastically reduced charge inhomogeneity to mere electrons per square micrometer, representing an order-of-magnitude improvement over previous designs. Such cleanliness enabled the direct observation of Landau quantization – a hallmark of quantum behavior in 2D electron systems – at magnetic field strengths as low as 5–6 milli-Tesla. By comparison, typical graphene devices require magnetic fields hundreds of times stronger to manifest similar quantum effects. The underlying physics stems from minimized scattering caused by long-range electric field fluctuations, pushing transport mobility values beyond 20 million cm²/Vs and surpassing the quantum mobility of the best GaAs electron gases.

The second study, conducted by Sir Andre Geim’s group at The University of Manchester with co-leadership by Dr. Daniil Domaretskiy, took an alternate yet equally transformative approach. Instead of an additional graphene layer, this team positioned graphene less than a nanometer away from a metallic graphite gate, separated by an ultrathin dielectric spacer comprising only three to four layers of hexagonal boron nitride. This proximity granted exceptionally strong Coulomb screening, sharply suppressing charge disorder and bringing the electron-hole puddle density down to around 3×10⁷ cm⁻² — the equivalent of one extraneous charge per 100 million carbon atoms near charge neutrality.

The devices fabricated using this proximity screening technique demonstrated Hall mobilities surpassing 60 million cm²/Vs, eclipsing even the most sophisticated GaAs systems. Moreover, the quantum Hall effect, ordinarily observed at magnetic fields of several Tesla, was clearly visible at fields below 5 milli-Tesla. Equally striking were Shubnikov–de Haas oscillations—another quantum signature—which appeared at an astonishingly low field of just 1 milli-Tesla, a value comparable to Earth’s intrinsic magnetic field strength.

Together, these two complementary methodologies tackle the inherent problem of charged defect-induced disorder from different angles. The twist-angle graphene stacking design offers an elegant and highly tunable means of screening, allowing researchers to explore a broad parameter space in terms of electronic interaction and coupling. On the flip side, the proximity metallic screening method presents a clean, direct probe of intrinsic graphene properties without additional parasitic signals from the screening layer. This latter approach enables pristine observation of quantum phenomena like clean Quantum Hall plateaus at remarkably low magnetic fields.

Assistant Professor Berdyugin underscores the significance of these achievements, emphasizing how this expanded experimental toolkit opens new avenues for fundamental inquiry and technological innovation. The unparalleled purity achieved in these graphene devices is poised to accelerate progress in quantum metrology, where precision measurements rely on stable quantum Hall effects, as well as in ultra-sensitive electronic sensors that base their functionality on faultless charge transport. Furthermore, the record mobilities enabled here are vital for advancing next-generation electronics optimized for speed and energy conservation.

Looking toward the future, the research teams plan to extend these methods to more intricate graphene-based heterostructures, especially those hosting moiré quantum materials. These complex structures exhibit a plethora of correlated electron phenomena, including unconventional superconductivity and exotic many-body states, which have captivated condensed matter physicists worldwide. The breakthroughs in controlling disorder and enhancing mobility promise to provide cleaner platforms for probing these enigmatic quantum phases.

In reflection, this watershed moment in graphene research dramatically alters the boundaries of what was thought possible. The immense reduction in electronic disorder achieved by these novel screening techniques not only sets new world records but also fundamentally changes the landscape of 2D material physics. As Mr. Ian Babich, a doctoral researcher involved in the work, remarks, “The performance ceiling we now break opens up an entire new physics landscape, inspiring further exploration and technological breakthroughs.”

These findings exemplify how a meticulous combination of material engineering, precise nanofabrication, and fundamental physics theory can culminate in unprecedented scientific and technological milestones. With the promise of ultra-clean, ultra-fast graphene electronics and scalable quantum devices on the horizon, the age of graphene as a field-defining two-dimensional material is truly entering a new era of discovery and application.

Subject of Research: Not applicable

Article Title: Milli-Tesla quantization enabled by tuneable Coulomb screening in large-angle twisted graphene

News Publication Date: 11-Aug-2025

Web References:

• https://www.nature.com/articles/s41467-025-62492-5
• https://www.nature.com/articles/s41586-025-09386-0

Image Credits: College of Design and Engineering at NUS

Keywords

Two dimensional materials, Physics, Solid state physics, Transport phenomena, Quantum matter

The core innovation lies in the device’s unique dual-mode operational capability. Traditionally, photodetectors rely on external power sources and have limited angular sensitivity, constraining their functionality in practical scenarios. This newly reported device overcomes these limitations by delivering wide-angle, self-driven photodetection, while simultaneously enabling efficient neuromorphic computing operations at ultralow power consumption levels. Such an integration is unprecedented, elegantly combining light detection with brain-inspired computation on a transparent substrate that allows for seamless embedding in various environments without visual interference.

At the heart of this technological breakthrough is an intricate design that employs transparent materials engineered to achieve both photodetection and neuromorphic functionalities simultaneously. By leveraging carefully tuned semiconductor components layered within an optically clear matrix, the researchers succeeded in fabricating a device that can respond to light stimuli from virtually any direction—accomplishing what they term 360° quasi-omnidirectional photodetection. This capability dramatically expands the spatial coverage of light sensing beyond conventional planar devices, ensuring consistent performance regardless of illumination angle.

Moreover, the device operates in a truly self-driven mode. In other words, it harnesses the incident light not only as the stimulus to detect but also as the sole energy source driving its operational processes. This attribute eliminates the reliance on battery power or external electrical sources, making the photodetector highly suitable for sustainable and autonomous applications. The energy harvested from ambient light is efficiently converted into electrical signals that subsequently feed into the neuromorphic computing elements embedded within the device.

Neuromorphic computing, inspired by the human brain’s neural architecture, represents a paradigm shift in information processing by mimicking synaptic functionalities at a hardware level. The device integrates synaptic transistors that emulate neuronal behavior, allowing it to process and interpret optical signals in situ—reducing latency and power consumption while improving computational efficiency. This synergy between sensing and processing within a single transparent entity eliminates the need for separate components and complex wiring, simplifying device architecture and enhancing scalability.

The ultralow-power nature of this neuromorphic unit is particularly impressive. By utilizing novel materials with low threshold voltages and energy-efficient switching dynamics, the researchers achieved computation at power consumption levels orders of magnitude below traditional processors. This feature is crucial for deploying electronics in portable or remote scenarios where power budgets are severely constrained or where perpetual operation on harvested energy is paramount.

Crucially, the transparent quality of the device does not compromise its performance. Conventional electronic devices often introduce opacity and bulky form factors, limiting their integration into applications requiring aesthetic discretion or unhindered light transmission, such as augmented reality glasses or smart windows. This transparent device maintains high optical clarity, ensuring it can be layered onto or embedded within surfaces and displays without detracting from their appearance or function.

The fabrication process adopted in this research combines advanced materials synthesis with precision layering techniques. The semiconductor layers responsible for light absorption and photogeneration are carefully deposited to maximize responsivity while maintaining transparency. The neuromorphic components, composed of emerging two-dimensional materials and oxide semiconductors, are integrated using state-of-the-art lithographic methods that preserve the delicate balance between optical and electrical functionality.

An exhaustive characterization of the device reveals its robust performance over a wide spectral range and diverse angles of incidence. The photodetection capability remains stable and sensitive even under varying environmental lighting conditions, a testament to the device’s adaptability and reliability. Furthermore, the synaptic behavior exhibits long-term plasticity and rapid response times, essential traits for practical neuromorphic applications requiring learning and adaptation.

Potential applications for this dual-mode device span a vast technological landscape. In the realm of wearable health monitors, the device could enable continuous, self-powered sensing of environmental light factors coupled with on-site processing for real-time feedback. In robotics and autonomous systems, it could underpin intelligent vision systems that adaptively filter and interpret optical signals with minimal energy overhead. Moreover, integration into building materials like transparent facades could allow smart windows to dynamically respond to light stimuli and perform local data processing, contributing to energy-efficient architectures.

This innovation stands at the confluence of multiple research frontiers—optoelectronics, neuromorphic engineering, and materials science—showcasing what interdisciplinary collaboration can achieve. Its dual-mode operation, self-sufficiency, and transparency collectively push the boundaries of what is currently possible in integrated photodetection and computation systems. The work lays a solid foundation for future devices that could seamlessly blend into everyday objects, smart environments, and intelligent interfaces with minimal energy and visual cost.

To harness the full commercial and societal impact of this technology, further developments are anticipated. Scaling the device to larger areas, enhancing durability under diverse environmental stresses, and incorporating complex neuromorphic learning algorithms will be pivotal. Additionally, exploring new transparent materials with even greater carrier mobilities and synaptic efficiencies could amplify the device’s capabilities, paving the way toward fully autonomous, intelligent, and visually unobtrusive sensors.

In conclusion, the advent of this dual-mode transparent photodetector and neuromorphic computing device represents a bold stride forward. It unites wide-angle light sensing and brain-like computation within an ultralow-power, self-supporting, and visually transparent architecture, setting the stage for revolutionary applications across multiple domains. As the research community builds upon these findings, the dream of ambiently powered, intelligent, and invisible electronics edges tantalizingly closer to reality.

Subject of Research: Dual-mode transparent device combining 360° quasi-omnidirectional self-driven photodetection and ultralow-power neuromorphic computing

Article Title: A dual-mode transparent device for 360° quasi-omnidirectional self-driven photodetection and efficient ultralow-power neuromorphic computing

Article References:
Jiang, M., Zhao, Y., Liu, T. et al. A dual-mode transparent device for 360° quasi-omnidirectional self-driven photodetection and efficient ultralow-power neuromorphic computing. Light Sci Appl 14, 273 (2025). https://doi.org/10.1038/s41377-025-01991-y

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41377-025-01991-y

Silicon, the semiconductor backbone of modern electronics and photovoltaic technologies, typically undergoes an ultrafast phase transition known as nonthermal melting when subjected to a single, intense ultrashort laser pulse. Unlike traditional melting, which is thermally driven by lattice heating, nonthermal melting occurs as a direct consequence of the rapid excitation of electrons, leading to a destabilization of the atomic lattice before any significant temperature rise. This process unfolds on the order of femtoseconds, making real-time observation and control an extraordinary challenge.

Leveraging advanced ab initio molecular dynamics simulations—theoretically rigorous computational models based on fundamental quantum mechanical principles—the researchers simulated the atomic trajectories and electronic responses of silicon subjected to engineered laser pulse sequences. Their findings reveal that delivering two laser pulses with an exquisitely timed delay of approximately 126 femtoseconds can interrupt the onset of nonthermal melting. The first pulse initiates atomic displacements by promoting electrons to excited states, setting the lattice into motion. However, the subsequent pulse interacts with these atomic vibrations, effectively imposing a counteracting influence that ‘locks’ the system into a metastable solid state instead of allowing it to smoothly transition to a molten phase.

This metastable state’s stability is not merely a transient pause but a distinct non-equilibrium phase characterized by unique electronic and vibrational properties. Remarkably, the band gap—the energy range where no electron states exist—remains only slightly reduced from that of crystalline silicon, a crucial factor governing the material’s electrical conductivity and optical behavior. Additionally, the vibrational modes of the lattice, represented by phonons, exhibit cooler and more coherent dynamics, as if the atomic motion is ‘frozen’ by the second laser pulse’s interference. This dynamic manipulation of phonons highlights a new realm of controlling lattice energy and heat flow at ultrafast timescales.

The implications of this study are manifold. By demonstrating a method to precisely control phase transitions in silicon on femtosecond timescales, the research sets the stage for similar experimental strategies to be applied across a spectrum of technologically relevant materials. The ability to temporally halt or steer ultrafast melting provides a powerful tool for creating and stabilizing new phases that are inaccessible under equilibrium conditions, potentially enabling novel material properties tailored by light.

Moreover, this approach could revolutionize ultrafast spectroscopy experiments, where understanding energy transfer pathways between electrons and atomic nuclei remains a fundamental challenge. Temporally freezing the lattice motion allows researchers to isolate and study electron dynamics without the concurrent complications of structural rearrangement, thus enhancing the accuracy and interpretability of ultrafast measurements. This methodological breakthrough promises to deepen our grasp of fundamental light–matter interactions, a domain critical for the advancement of quantum technologies and high-speed optoelectronic devices.

The success of this elaborate pulse-timing scheme rests on an intricate interplay of quantum mechanics and lattice dynamics. The initial pulse deposits energy into the electronic subsystem, elevating electrons to excited states that weaken interatomic bonds. Prior to atomic disordering, the delayed second pulse arrives, synchronized with the oscillatory atomic motions induced by the first excitation. This carefully timed interaction suppresses the lattice instability that would otherwise cascade into melting, effectively leveraging quantum coherence and constructive interference principles to guide the system

Piezoelectric materials, which generate electrical charge in response to mechanical stress, serve as pivotal components in an array of modern technologies that touch daily life. Their prevalence spans from the cluttered interiors of cell phones, where they act as precise filters to suppress signal noise, to automotive safety systems that rely on their rapid sensor response to trigger airbags and monitor tire integrity. Enhancing the piezoelectric effect in these materials translates directly into improvements in sensitivity, efficiency, and durability, fundamentally improving the performance of countless devices that rely on these phenomena.

The team’s innovative approach involves subjecting scandium aluminum nitride thin films to a meticulously controlled annealing process—heating the material to 700 degrees Celsius for a full two hours within a specialized chamber. This thermal treatment fosters critical atomic rearrangements within the thin crystal layers, correcting structural defects that typically impede their piezoelectric response. The result is an extraordinary eight-fold increase in piezoelectricity compared to the properties seen in commercially available materials, effectively pushing the envelope toward new possibilities in device engineering.

Central to this enhancement is the reorientation of microscopic structural “grains” within the material. These grains, initially misaligned during the film’s growth phase, contribute unevenly to the piezoelectric effect due to their directional sensitivity. The annealing process supplies sufficient thermal energy to coax these grains into better alignment with the material’s overall crystalline axis. This realignment maximizes their collective contribution, substantially magnifying the measurable piezoelectric response and thereby enhancing sensor performance and energy conversion efficiencies.

The implications of such a leap are manifold and expansive. Enhanced piezoelectric films crafted through this simple yet effective step could lead to the creation of ultrasensitive pressure and vibration sensors crucial for monitoring structural health in aerospace engineering or advanced medical ultrasound imaging. Moreover, their application extends into smart city infrastructure, where energy-harvesting traffic lights powered by the vibrations of passing trucks could become a reality, promoting sustainable urban energy solutions.

The engineering team’s exploration of this processing technique is ongoing, with plans to extend their study to scandium aluminum nitride films synthesized via molecular beam epitaxy. This technique is known to produce exceptionally high-quality crystalline films, opening the door for even further improvements in piezoelectric performance. The combination of advanced material growth methods with post-processing annealing could redefine benchmarks in piezoelectric efficiency and reliability.

Remarkably, the annealing process devised by the researchers aligns closely with existing industrial fabrication standards, meaning the pathway to commercial adoption is streamlined. Industry players stand to upgrade their semiconductor components dramatically without incurring substantial additional manufacturing costs or overhauling established workflows. This seamless integration amplifies the innovation’s appeal, promising rapid deployment of more capable piezoelectric devices in both commercial and defense sectors.

Funding for this trailblazing research comes from the Defense Advanced Research Projects Agency (DARPA) as part of a collaborative project involving the University of Florida, the University of Michigan College of Engineering, and the Army Research Office. This partnership aims to leverage improved piezoelectric materials for creating next-generation atomic clocks with hyper-precision synchronization capabilities, which hold critical importance for national defense and communication systems.

The multi-institutional nature of the work further enhances the rigor and applicability of the findings. Contributions from researchers at the University of Florida and Pennsylvania State University encompassed interdisciplinary expertise that enriched the study’s scope and depth, ensuring robustness in both theoretical insight and experimental verification. The well-equipped Lurie Nanofabrication Facility and the Michigan Center for Materials Characterization provided essential infrastructure for processing and evaluating the advanced films.

Intellectual property considerations are already being addressed, with patent applications underway and active pursuits of industrial partnerships through the University of Michigan’s Innovation Partnerships program. This strategy indicates clear intent to move beyond academia and realize tangible commercial impacts, accelerating the translation of this technology from lab bench to market-ready devices.

Professor Zetian Mi, whose credentials also include appointments in electrical and computer engineering and materials science and engineering, leads these transformative efforts. His vision integrates materials science innovation with practical engineering solutions that promise broad societal benefit. The comprehensive study detailing the enhancement mechanisms and material characterizations has been published in Nature Communications, providing open insight into the scientific community to foster further advances.

This breakthrough shines a spotlight on the latent potential locked within well-studied semiconductor materials and underscores how revisiting fabrication processes with fresh perspectives can yield exponential improvements. The engineering simplicity paired with profound functional gains serves as a potent reminder that innovation transcends complexity, and even incremental process tweaks can redefine the technological landscape.

As the scientific and industrial communities continue to digest and build upon these findings, the future of piezoelectric devices looks brighter than ever. From empowering smarter energy harvesting and ultra-precise sensing to enabling new frontiers in medical and defense technologies, this enhancement in scandium aluminum nitride films epitomizes the transformative power of marrying material science with innovative fabrication techniques.

Subject of Research: Enhancement of piezoelectric properties in semiconductor materials via thermal annealing

Article Title: Unprecedented enhancement of piezoelectricity of wurtzite nitride semiconductors via thermal annealing

Web References:

• Study DOI: https://doi.org/10.1038/s41467-025-59179-2
• University of Michigan Engineering: https://mi.engin.umich.edu/
• Lurie Nanofabrication Facility: https://lnf.umich.edu/
• Michigan Center for Materials Characterization: https://mc2.engin.umich.edu/

References:

• Mi, Z., Mondal, S., Tanim, M. M. H., et al. (2024). Unprecedented enhancement of piezoelectricity of wurtzite nitride semiconductors via thermal annealing. Nature Communications. DOI: 10.1038/s41467-025-59179-2

Keywords

Piezoelectricity, Scandium Aluminum Nitride, Semiconductor Materials, Thermal Annealing, Microelectronics, Photonics, Materials Engineering, Electrical Engineering, Materials Science, Condensed Matter Physics