An international research team, led by the National University of Singapore (NUS), has shown 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 – similarly to how oil, honey and other viscous fluids flow more easily as they are heated on a stove.
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.
THz radiation has huge potential. 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. THz vision can also enable observational astronomy, allowing scientists to observe distant galaxies and exoplanets that cannot be seen by visible light.
However, until recently, detecting THz radiation has been a significant challenge. THz waves are too fast for traditional semiconductor chips to handle and too slow for conventional optoelectronic devices.
This recent study showed that by harnessing the viscosity reduction effect, scientists can create innovative devices that can detect THz waves by sensing the changes in electrical resistance. The team has developed 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.
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 team is working on optimizing these viscous electron bolometers for practical applications.