#plasmonics

Terahertz microscope reveals the motion of superconducting electrons

You can tell a lot about a material based on the type of light shining at it: Optical light illuminates a material's surface, while X-rays reveal its internal structures and infrared captures a material's radiating heat. Now, MIT physicists have used terahertz light to reveal inherent, quantum vibrations in a superconducting material, which have not been observable until now. Terahertz light is a form of energy that lies between microwaves and infrared radiation on the electromagnetic spectrum. It oscillates over a trillion times per second—just the right pace to match how atoms and electrons naturally vibrate inside materials. Ideally, this makes terahertz light the perfect tool to probe these motions.

Plasma Balls

Tiny nanoparticles have huge potential inside our bodies. These hexagonal specks of magnesium, each 50,000 smaller than a beach ball, could be injected into our tissues then zapped by lasers – the light particles (photons) collide with electrons buzzing around the surface of the metal, generating a haze of rippling waves called plasmons around each particle. Plasmonic waves are sensitive to changes in their surroundings, so may be used to snoop on chemical reactions happening nearby, such as a patient’s metabolism. Here computer model simulations (top row), and experiments (bottom) show how different wavelengths of light create different electric field patterns around the particles. Though usually completely harmless, with a different setup, plasmonic waves could be targeted to fry cancer cells. These magnesium nanoparticles are cheaper than those made from gold or silver, and their unique shape is allowing nanoengineers to dream up useful new structures.

Written by John Ankers

Image by the Ringe Group/Rice University

Department of Material Science and Nanoengineering and Department of Chemistry, Rice University, Houston, Texas, USA

Image copyright held by the original authors

Published in Nano Letters, May 2018

Sprinkling nanoparticles on spintronics

Today, I want to walk you through a deceptively simple innovation from the lab at Loughborough University (PI: Prof Marco Peccianti): what happens when we decorate a spintronic heterostructure with a sparse layer of plasmonic nanoparticles? This isn't just a lab curiosity—it's a step toward making terahertz sources more efficient, compact, and practical for real-world applications like high-speed communications, noninvasive imaging, and advanced spectroscopy. Spintronic THz emitters: The foundation Spintronic terahertz emitters rely on a thin, multilayer stack—typically heavy metal like tungsten (W), a ferromagnetic layer such as iron (Fe), and a platinum (Pt) cap. A femtosecond laser pulse strikes the structure, rapidly heating electrons and generating a pure spin current through spin-orbit torque effects.

Ultra-thin sodium films offer low-cost alternative to gold and silver in optical technologies

From solar panels to next-generation medical devices, many emerging technologies rely on materials that can manipulate light with extreme precision. These materials—called plasmonic materials—are typically made from expensive metals like gold or silver. But what if a cheaper, more abundant metal could do the job just as well or better? That's the question a team of researchers set out to explore. The challenge? While sodium is abundant and lightweight, it's also notoriously unstable and difficult to work with in the presence of air or moisture—two unavoidable parts of real-world conditions. Until now, this has kept it off the table for practical optical applications. Researchers from Yale University, Oakland University, and Cornell University have teamed up to change that. By developing a new technique for structuring sodium into ultra-thin, precisely patterned films, they found a way to stabilize the metal and make it perform exceptionally well in light-based applications.

Diamond continues to shine: New properties discovered in diamond semiconductors

Diamond, often celebrated for its unmatched hardness and transparency, has emerged as an exceptional material for high-power electronics and next-generation quantum optics. Diamond can be engineered to be as electrically conductive as a metal, by introducing impurities such as the element boron. Researchers from Case Western Reserve University and the University of Illinois Urbana-Champaign have now discovered another interesting property in diamonds with added boron, known as boron-doped diamonds. Their findings could pave the way for new types of biomedical and quantum optical devices—faster, more efficient, and capable of processing information in ways that classical technologies cannot. Their results are published in Nature Communications.

Stretchable waveguides maintain stable transmission even when bent or twisted

Researchers have designed and demonstrated stretchable waveguides that maintain efficient, stable signal transmission of surface plasmon polaritons even when bent, twisted or stretched. These plasmonic waveguides could make it possible to seamlessly embed advanced sensing, communication and health monitoring functions into everyday wearable materials. Plasmonic waveguides are tiny structures that guide light by coupling it with electrons on a metal surface. The new flexible waveguides transmit what are known as spoof surface plasmon polaritons, which are formed with longer wavelengths—radio frequencies in this case—rather than the conventional infrared or visible light. "Although our work is still at the research stage, it highlights the exciting possibility of merging advanced electromagnetic technologies with soft, stretchable materials," said research team leader Zuojia Wang from Zhejiang University. "This brings us closer to a future where advanced health care and connectivity are integrated into what we wear."