New research into quantum materials like graphene shows that electrons can behave like viscous fluids, opening up possibilities for faster and more efficient electronic devices.
This breakthrough has led to the development of devices such as the viscous electron bolometer, which could improve technologies from internet speeds to non-invasive medical scans.
In high school science, we learned that connecting a cable to an electrical circuit starts a flow of electrons, providing power to everything from lights to phones.
Traditionally, we’ve understood electron behavior in metals and semiconductors using a simple model. In this view, electrons are like tiny, independent particles — similar to cars moving freely on an open highway, rarely interacting with each other. This straightforward model has long been the foundation of electronics, shaping how we design the devices that power modern life.
However, this traditional view doesn’t fully explain the behavior of electrons in certain emerging quantum materials, such as graphene — a highly conductive, ultrathin material. In graphene, electrons don’t move independently but instead flow collectively, resembling the movement of a viscous fluid, like oil.
This finding is more than just a quirky observation. It could be transformative for the future development of a broad range of technologies.
Exploring Graphene’s Properties
In Assistant Professor Denis Bandurin’s research lab in the College of Design and Engineering at the National University of Singapore, they’re exploring how quantum materials interact with electromagnetic radiation at the nanoscale to uncover new scientific phenomena and their potential use in developing future technologies.
In a recent study, published in Nature Nanotechnology, they reported that when graphene is exposed to electromagnetic radiation of terahertz frequencies, electron fluid heats up and its viscosity is drastically reduced, resulting in lower electrical resistance — much like how oil, honey, and other viscous fluids flow more easily as they are heated on a stove.
Advancements in THz Technology
Why is this exciting?
Terahertz (THz) waves are a special and technologically challenging part of the electromagnetic spectrum — situated between microwaves and infrared light — that have a vast range of potential applications. Being able to detect THz waves could unlock major advances in technologies
In communications for example, current Wi-Fi technology operates at several GHz, limiting how much data can be transmitted. THz radiation, with its much higher frequency, could serve as the “carrier frequency” for ultrafast, beyond 5G networks, enabling faster data transfer for Internet of Things (IoT) connected devices, self-driving cars and countless other applications.
In medical imaging and industrial quality control, THz waves can penetrate many materials, making them useful for non-invasive scans. They are also safer than X-rays, providing a highly selective and precise imaging tool.
Going further afield, THz vision enables observational astronomy, allowing scientists to observe distant galaxies and exoplanets that cannot be seen by visible light.
The Role of Viscous Electronics in Modern Technology
THz radiation therefore offers huge potential. The problem is that, until recently, detecting it has been a significant challenge. THz waves are too fast for traditional semiconductor chips to handle and too slow for conventional optoelectronic devices.
This study shows that by harnessing the viscosity reduction effect we can create innovative devices that can detect THz waves by sensing the changes in electrical resistance. Indeed, as reported in the paper, they’ve been able to build a new class of electronic device called a viscous electron bolometer.
Representing the first practical, real-world application of viscous electronics — a concept that was once thought to be purely theoretical — these bolometers are able to sense changes in resistance extremely accurately and quickly, operating, in principle, at the pico-second scale. In other words, trillionths of a second.
Future of Electronic Devices
Understanding and exploiting the way electrons move together as a collective fluid opens the way for us to completely rethink the design of electronic devices. With this in mind, the research team is actively working on optimizing these viscous electron bolometers for practical applications.
As we uncover more secrets in the emerging world of quantum materials, it’s clear that traditional models of electron behavior are no longer sufficient. By embracing this new understanding of viscous electronics, scientists could be on the verge of unlocking a new wave of technological possibilities.
Reference: “Viscous terahertz photoconductivity of hydrodynamic electrons in graphene” by M. Kravtsov, A. L. Shilov, Y. Yang, T. Pryadilin, M. A. Kashchenko, O. Popova, M. Titova, D. Voropaev, Y. Wang, K. Shein, I. Gayduchenko, G. N. Goltsman, M. Lukianov, A. Kudriashov, T. Taniguchi, K. Watanabe, D. A. Svintsov, S. Adam, K. S. Novoselov, A. Principi and D. A. Bandurin, 7 October 2024, Nature Nanotechnology.
DOI: 10.1038/s41565-024-01795-y