viscous-electron-quantum-materials-THz-wave-detection

Exploring Viscous Electron Flow in Quantum Materials: The Future of Terahertz Wave Detection

Introduction to Electron Flow in Electronics

In traditional electronics, the behavior of electrons has long been understood through a simple model, where they move like individual particles, much like cars on a highway. This model has been foundational to modern electronics, guiding the development of devices and technologies we rely on today.

However, this model starts to break down when to quantum materials, such as graphene, where electron behaviour deviates from the norm.

Quantum Materials and Viscous Electron Flow

Graphene, a highly conductive and ultrathin material, presents an exciting departure from the conventional understanding of electron flow. In graphene, electrons move collectively, behaving more like a viscous fluid, such as oil or honey, rather than independent particles.

This viscous electron flow offers transformative possibilities for future technological innovations, particularly when investigating how these materials interact with electromagnetic radiation.

Research by NUS: Investigating Electromagnetic Radiation at the Nanoscale

Assistant Professor Denis Bandurin and his team from the Department of Materials Science and Engineering at the National University of Singapore (NUS) are pushing the boundaries of this field. Their research focuses on how quantum materials interact with electromagnetic advancing scientific knowledge and developing future technologies.

The Impact of Terahertz Radiation on Graphene

In a groundbreaking study published in Nature Nanotechnology, the NUS team discovered that exposing graphene to terahertz (THz) electromagnetic radiation causes the electron fluid to heat up. This heating reduces the viscosity of the electron fluid, much like how oil flows more freely when heated. This phenomenon also lowers the electrical resistance within graphene, which opens up new possibilities for its use in advanced electronic devices.

Pushing the Boundaries of Terahertz Wave Detection

Terahertz wave occupy a unique region of the electromagnetic spectrum between microwaves and infrared light. While difficult to detect with traditional technologies, these waves hold enormous potential for communications, medical imaging, industrial quality control, and even astronomy.

• In communications, Thz radiation could be a game-changer for beyond 5G networks, offering faster data transmission for IoT devices, autonomous vehicles, and more.
• In medical imaging, Thz waves can penetrate materials for non-invasive scans, providing a safer alternative to X-rays.
• In astronomy, Thz vision enables the study of galaxies and exoplanets hidden from visible light.

Detecting these waves has been a challenge due to their speed—too fast for traditional semiconductor chips, but too slow for standard optoelectronic devices. However, recent advances in quantum materials may offer a solution.

The Viscous Electron Bolometer: A Revolutionary Device

One of the most significant outcomes of the NUS team's research is the development of the viscous electron bolometer. This device harnesses the reduced viscosity of graphene's electron fluid to detect terahertz waves.

These bolometers represent the first practical application of viscous electronics, a concept that was once theoretical. They are capable of detecting changes in electrical resistance with unprecedented precision, operating in the pico-second range (trillionths of a second).

By leveraging the fluid-like behavior of electrons, these bolometers could revolutionize the design of electronic devices, opening the door to advanced sensing technologies.

Future Implications of Viscous Electronics

The study of quantum materials like graphene is revealing the limitations of conventional models of electron behaviour. By embracing the viscous electronics paradigm, we may be on the brink of a new era in technological innovation. As researchers like Asst. Prof. Bandurin continue to refine viscous electron bolometers, we can expect significant advances in electronics, communications, and beyond.

Conclusion: A New Era of Technological Innovation

The discovery of viscous electron flow in quantum materials like graphene is setting the stage for the development of advnaced electronic devices. With applications ranging from ultrafast communications to non-invasive medical imaging, the potential of these technologies is immense. As researchers continue to explore the possibilities, the world of electronics may soon undergo a dramatic transformation.

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Twistronics and 2D material technology

Revolutionary Device Optimizes 2D Material Manipulation for Twistronics Platforms

Breakthrough in Condensed-Matter Physics

In 2018, a discovery shook the foundations of condensed-matter physics: Two ultra-thin carbon layers stacked at a slight angle formed a superconductor, with their electrical properties modifiable through twist-angle adjustments. This breakthrough led to the emergence of "Twistronics," a field pioneered in a landmark paper by Yuan Cao, then an MIT graduate student and currently a Harvard Junior Fellow.

Advancements in Twistronics

Collaborative Efforts in Twistronics Research

Together with Harvard's Amir Yacoby, Eric Mazur, and others, Cao and his colleagues have enhanced their foundational research, developing a simplified method for twisting and studying multiple materials, thereby fostering further twistronics advancements.

New Device Simplifies Material Manipulation

In a recent paper published in Nature, the team details a fingernail-sized machine capable of twisting thin materials at will, eliminating the need for fabricating twisted devices individually. These thin, 2D materials, with easily manipulated properties, hold vast potential for advancing high-performance transistors, optical technologies like solar cells, and quantum computing.

Key Insights and Implications

Expert Commentary on the Breakthrough

Yacoby, a Harvard Professor of Physics and Applied Physics, remarked, "This breakthrough simplifies the process of twisting 2D materials to the level of controlling electron density. Previously, adjusting density was the main method for discovering novel phases in low-dimensional matter; now, with control over both density and twist angle, we unlock countless possibilities for new discoveries."

Overcoming Challenges in Twisting Devices

During his time as a graduate student in Pablo Jarillo-Herrero's lab at MIT, Cao successfully created twisted bilayer graphene. Despite the excitement surrounding this accomplishment, it was accompanied by difficulties in consistently replicating the twisting process.

Development of the MEGA2D Platform

According to Cao, the challenge of producing each twisted device was significant, with the need for numerous unique samples complicating the scientific process. The team sought to simplify this by developing a micromachine that could twist two layers of material on demand, resulting in the creation of the MEGA2D, a MEMS (micro-electromechanical system)-based actuation platform for 2D materials.

Collaboration and Future Prospects

Collaborative Design of the MEGA2D Device

The development of this new tool kit was a collaborative effort between the Yacoby and Mazur labs, and it is adaptable for use with graphene as well as other materials.

Future Applications and Discoveries

As an assistant professor at the University of California Berkeley, Cao stated, "Our MEGA2D technology offers a new "Knob" that we expect will quickly unravel many of the complex issues in twisted graphene and other materials. Moreover, it will likely lead to further groundbreaking discoveries."

Research Findings and Potential

Demonstrating the Device's Utility

In their publication, the researchers showcased the effectiveness of their device with two sheets of hexagonal boron nitride, a material akin to graphene. They investigated the optical properties of the bilayer device and discovered quasiparticles exhibiting sought-after topological properties.

Scientific and Technological Implications

Their new system's ease of use unlocks multiple scientific avenues, such as leveraging hexagonal boron nitride twistronics to engineer light sources that enhance low-loss optical communication.

Conclusion

Optimism for Broader Adoption

Cao expressed optimism that their methodology will gain traction among other researchers in this thriving field, enabling widespread benefits from these new capabilities.

Insights from the Primary Author

The primary author of the paper, Haoning Tang, a distinguished nanoscience and optics specialist and postdoctoral researcher in Mazur's lab as well as a Harvard Quantum Initiative fellow, remarked that creating the MEGA2D technology was a prolonged journey of experimentation and refinement.

"We initially lacked comprehensive knowledge on real-time control of 2D material interfaces, and the conventional techniques proved inadequate," she noted. "Through extensive hours in the clean room and numerous iterations of the MEMS design--despite several setbacks--we eventually Nanofabrication was conducted at Harvard's Center for Nanoscale Systems, where Tang acknowledged the critical technical support provided by the staff.

Recognition of the Nanofabrication Achievement

Mazur, the Balkanski Professor of Physics and Applied Physics, described the integration of MEMS technology with a bilayer structure in nanofabrication as an impressive achievement. He noted that the ability to adjust the nonlinear response of the device paves the way for novel innovations in optics photonics.

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Wearable Graphene Sensor For Strain Detection

Innovative Graphene-Based Wearable Sensor Allows Detection and Broadcast of Silently Mouthed Phrases

Introduction

The development of a 'smart' wearable choker featuring ultrasensitive textile strain sensors may significantly advance the Silent Speech Interface (SSI) domain, researchers claim.

SSI systems offer a breakthrough solution for scenarios where verbal communication is compromised, such as in noisy environments or for individuals with speech difficulties, facilitating speechless communication via electronic lip-reading and human-computer interaction.

Development and Technology

Advanced Sensor Design

Researchers at the University of Cambridge have developed a textile strain sensor with a graphene overlay, offering enhanced robustness in speech recognition, even in environments with significant background noise.

The smart choker, worn around the neck, detects subtle micro-movements in the throat, which the strain sensor converts into electrical signals. These signals are processed by brain-inspired computing models for speech recognition, enabling the detection of even silently mouthed words, potentially aiding individuals unable to speak after laryngeal surgery.

Innovative Design Features

The innovative design of the smart choker incorporates organized cracks in graphene-coated textiles. This structured graphene layer dramatically improves the strain sensor's sensitivity, allowing it to capture subtle throat micro-movements and extract speech signals rich in detail. The signals are then decoded with a high 95.25% accuracy using an efficient neural network.

Results and Presentation

Study and Findings

The study, featured in npj Flexible Electronics, introduces a promising non-invasive solution for wearable SSI systems, opening the door to seamless, natural, silent communication in a wide range of settings.

This robust SSI system is capable of decoding a vast range of words and seamlessly adapting to new users and vocabularies. It was presented live at the IEEE Biosensors 2024 event, engaging more than 180 participants.

Leadership and Research

Key Figures

Dr. Luigi G. Occhipinti, Director of Research in Smart Electronics, Bio-systems, and AI, and Head of the Occhipinti Group at the Electrical Engineering Division, played a key role in directing the research in partnership with the Cambridge Graphene Center.

According to Dr. Occhipinti, "The smart choker's user-friendly design enables it to perform effectively in real-world situations, handling a range of users from different genders, regions, and ethnic backgrounds, while accurately processing new and ambiguous words of varying lengths and familiarity, as well as different reading speeds."

System Performance and Fabrication

Precision and Efficiency

Our SSI system excels in precision and computational efficiency, accurately distinguishing speech from multiple users despite noise introduced by sensor imperfections, external environmental factors, or movements of the users themselves while using the device.

Fabrication and Durability

Additionally, our ultrasensitive textile strain sensor technology features a fabrication method that is bio-compatible, cost-effective, and scalable. It is designed for extended use, withstanding over 10,000 stretch-release cycles while ensuring stable and reliable electrical performance.

Conclusion

"In essence, the integration of our sensor design with advanced neural network optimization establishes a new benchmark in wearable silent speech communication technologies, providing a comfortable smart choker with pioneering capabilities."

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