A group of researchers at Cavendish Laboratory, along with colleagues at the universities of Augsburg (Germany) and Lancaster, have discovered a new physical effect when two-dimensional electron systems are subjected to terahertz waves.
Wladislaw Michailow showing the device in the clean room and a terahertz detector after manufacture. Image credit: Wladislaw Michailow.
Professor David Ritchie explains exactly what terahertz waves are.
We communicate via cell phones that transmit microwave radiation and use infrared cameras for night vision. Terahertz is the type of electromagnetic radiation that lies between microwave radiation and infrared radiation, but at the moment, there is a lack of sources and detectors of this type of radiation, which are cheap, efficient and easy to use. . This makes the widespread use of terahertz technology difficult.
David Ritchie, Professor and Head of the Semiconductor Physics Group, Cavendish Laboratory, Cambridge University
In 2002, researchers from the Semiconductor Physics group, in collaboration with researchers from Pisa and Turin in Italy, were the first to illustrate the operation of a quantum cascade laser at terahertz frequencies. Since then, the team has continued to examine and develop functional terahertz devices that incorporate metamaterials as modulators, as well as new types of detectors.
We assume that the lack of usable devices has been fixed. In this case, terahertz radiation could find application in security, materials science, communications and medicine. Terahertz waves, for example, can be used for images of cancerous tissue that is not visible to the naked eye.
They can be used in the new generation of fast and secure airport scanners that can distinguish between illegal and explosive drug drugs, as well as facilitate wireless communications even faster than those currently available.
Dr. Wladislaw Michailow details exactly what this discovery is.
We were developing a new type of terahertz detector, but by measuring its performance, it turned out to show a much stronger signal than should be expected in theory. So a new explanation came to us.
Dr. Wladislaw Michailow, first study author and junior researcher, Trinity College Cambridge
According to the researchers, the explanation lies in the way light interacts with matter. Matter takes light in the form of individual particles called photons at high frequencies. Einstein postulated this interpretation, which became the basis of quantum mechanics and explained the photoelectric effect.
This quantum photoexcitation is how smartphone cameras detect light, and it’s also how solar cells produce electricity from light.
The well-known photoelectric effect involves incident photons that release electrons from a conductive material: metal or semiconductor. In the three-dimensional case, photons in the ultraviolet or X-ray range can eject electrons into a vacuum, or they can be released in a medium-infrared dielectric to the visible range. The novelty is the finding of a method of quantum photoexcitation in the terahertz range that is almost identical to the photoelectric effect.
The fact that these effects may exist within highly conductive two-dimensional electron gases at much lower frequencies has not been understood so far, but we have been able to demonstrate this experimentally.
Dr. Wladislaw Michailow, first study author and junior researcher, Trinity College Cambridge
A colleague from the University of Augsburg in Germany created the quantitative theory of the effect and the research team published its observations in the prestigious journal Science Advances.
The phenomenon was called “photoelectric effect in the plane” by researchers. The researchers describe several advantages of using this effect for terahertz detection in the corresponding document. The magnitude of the photoresponse produced by incident terahertz radiation due to the “photoelectric effect in the plane” is much larger than expected from other previously known mechanisms for generating a terahertz photoresponse.
As a result, researchers believe that this effect will allow the construction of terahertz detectors with significantly higher sensitivity.
Professor Ritchie states: “This brings us one step closer to making terahertz technology usable in the real world.”
The study was funded by EPSRC HyperTerahertz projects (EP / P021859 / 1) and grant no. EP / S019383 / 1, the Schiff Foundation of the University of Cambridge, Trinity College Cambridge and the European Union’s Horizon 2020 research and innovation program Graphene Core 3 (grant no. 881603).
Magazine reference:
Michailow, W., et al. (2022) A photoelectric effect in the plane in two-dimensional electron systems for terahertz detection. Advances in Science. doi.org/10.1126/sciadv.abi8398.
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