Researchers at Würzburg have unveiled a groundbreaking nanometer-scale light antenna with surface properties that can be electrically modulated. This innovation may lead to the development of much quicker computer chips.
Current computers are hitting physical speed limits. Most semiconductor components can only function at a maximum frequency of a few gigahertz, translating to billions of calculations per second. This has led to modern systems relying on multiple chips to manage tasks, as increasing the speed of individual chips is no longer feasible. However, utilizing light (photons) instead of electricity (electrons) in computer chips could potentially enhance speeds by up to 1000 times.
Plasmonic resonators, often called “light antennas,” present a promising avenue for achieving this speed enhancement. These tiny metallic structures enable interactions between light and electrons, and their design allows them to engage with different frequencies of light.
Dr. Thorsten Feichtner, a physicist at Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, notes, “The problem is that we can’t effectively modulate plasmonic resonators yet, unlike transistors in traditional electronics. This limitation hampers the development of rapid light-based switches.”
Advancements in Charged Optical Antennas
A research team from JMU, in partnership with Southern Denmark University (SDU) in Odense, has made a major advancement in the modulation of light antennas. They have successfully attained electrical modulation, leading towards ultra-fast active plasmonics and, consequently, much quicker computer chips. Their findings were published in the journal Science Advances.
Rather than altering the entire resonator, the team concentrated on modifying its surface properties. They accomplished this by electrically contacting a single plasmonic resonator, specifically a gold nanorod. While the concept is straightforward, its realization required advanced nanofabrication techniques utilizing helium ion beams and gold nanocrystals. This innovative fabrication process was developed under the leadership of Professor Bert Hecht at the JMU Chair of Experimental Physics (Biophysics). High-precision measurement methods with a lock-in amplifier were critical for identifying the subtle but meaningful surface effects on the resonator.
Study leader Dr. Thorsten Feichtner elaborates: “The phenomenon we are leveraging is analogous to a Faraday cage. Similar to how electrons accumulate on a car’s exterior during a lightning strike to protect its passengers, excess electrons on the surface impact the optical characteristics of the resonators.”
Unexpected Quantum Phenomena
Previously, optical antennas were primarily understood using classical physics: the electrons within the metal would simply stop at the nanoparticle’s edge, much like water at a wharf. However, the Würzburg researchers’ measurements indicated resonance changes that cannot be accounted for by classical theories. Instead, the electrons appear to “spread out” at the junction of the metal and air, creating a gradual transition akin to a sandy shore meeting the ocean.
To elucidate these quantum phenomena, theorists at SDU Odense created a semi-classical model that integrates quantum characteristics into a surface parameter, allowing calculations to proceed with classical methods. “By altering the response functions of the surface, we blend classical and quantum effects into a cohesive model that enhances our understanding of surface interactions,” said Luka Zurak, a physicist at JMU and lead author of the study.
A New Research Domain with Promising Prospects
While the new model successfully mimics the experiments, the precise quantum effects at play on the metal surface remain uncertain. “However, this study enables the first targeted design of new antennas, allowing us to amplify or suppress specific quantum effects,” Thorsten Feichtner states.
Looking ahead, the researchers foresee even broader applications: Smaller resonators may lead to highly efficient optical modulators for technological use. Additionally, the influence of surface electrons on catalytic processes can be explored using the system introduced, potentially providing new insights into energy conversion and storage technologies.
