Terrahertz technology could enable advanced scanners for safety, medicine and materials science. It could also enable much faster wireless communication devices than is currently possible.
Scientists have discovered a new effect in two-dimensional conduction systems that promise improved terahertz detector performance.
The recent discovery of physics in two-dimensional conduction systems enables a new type of terahertz detector. Terahertz frequencies, located between microwave and infrared in the spectrum of electromagnetic radiation, could enable faster, safer and more efficient recording technologies, as well as much faster wireless telecommunications. The lack of efficient devices in the real world has hampered this development, but this new breakthrough brings us one step closer to these advanced technologies.
A new physical effect when two-dimensional electronic systems are exposed to terahertz waves was discovered by a team of scientists from the Cavendish Laboratory together with colleagues from the Universities of Augsburg (Germany) and Lancaster.
“The fact that such effects can exist within highly conductive, two-dimensional electronic gases at much lower frequencies has not been understood so far, but we have been able to prove it experimentally. - Vladislav Michailov
For starters, what are terahertz waves? “We communicate using mobile phones that emit microwave radiation and use infrared night vision cameras. Terrazhertz is a type of electromagnetic radiation that is located between microwave and infrared radiation “, explains prof. sources and detectors of this type of radiation, which would be cheap, efficient and easy to use. This hinders the widespread use of terahertz technology. “
Researchers from the Semiconductor Physics group, along with researchers from Pisa and Turin, Italy, were the first to demonstrate in 2002 the operation of a laser on terahertz frequencies, a quantum cascade laser. Since then, the group has continued to research terahertz physics and technology and is currently researching and developing functional terahertz devices that include metamaterials to form modulators, as well as new types of detectors.
Vladislav Michailov shows the device in a clean room and a terahertz detector after making it. Credit: Vladislav Mikhailov
If the shortage of usable devices is addressed, terahertz radiation could have many useful applications in security, materials science, communications, and medicine. For example, terahertz waves make it possible to record cancerous tissue that cannot be seen with the naked eye. They can be used in new generations of safe and fast airport scanners that enable the differentiation of drugs from illegal drugs and explosives, and they can be used to enable even faster wireless communication outside the latest technology.
So what is the recent discovery about? “We developed a new type of terahertz detector,” says Dr. Vladislav Michailov, a junior research associate at Trinity College Cambridge, “but when we measured his performance, it turned out to show a much stronger signal than we should have expected.” That’s how we came up with a new explanation. “
This explanation, scientists say, lies in the way light interacts with matter. At high frequencies, matter absorbs light in the form of individual particles - photons. This interpretation, first proposed by Einstein, formed the basis of quantum mechanics and was able to explain the photoelectric effect. This quantum photoexcitation is the way the cameras in our smartphones detect light; it is also what generates electricity from light in solar cells.
The well-known photoelectric effect consists of the release of electrons from a conductive material - a metal or semiconductor - by incident photons. In the three-dimensional case, electrons can be ejected in a vacuum using photons in the ultraviolet or X-ray range, or released into a dielectric in the mid-infrared to visible range. A novelty is the discovery of a quantum process of photoexcitation in the terahertz range, similar to the photoelectric effect. “The fact that such effects can exist within highly conductive, two-dimensional electron gases at much lower frequencies has not been understood so far,” explains Vladislav, the study’s first author, “but we could prove it experimentally.” in Augsburg, Germany, and an international team of researchers recently published their findings in a reputable journal Science Advances.
Researchers have called the phenomenon accordingly, as the “photoelectric effect in the plane”. In their paper, scientists describe several benefits of using this effect to detect terahertz. In particular, the magnitude of the photoresponse generated by incident terahertz radiation “photoelectric effect in the plane” is much larger than expected from other mechanisms known to lead to terahertz photoresponse. Therefore, scientists expect that this effect will enable the production of terahertz detectors with significantly higher sensitivity.
“This brings us one step closer to making terahertz technology usable in the real world,” concludes Professor Richie.
Reference: “Photoelectric effect in the plane in two-dimensional electronic systems for terahertz detection” by Vladislav Michailov, Peter Spencer, Nikita V. Almond, Stephen J. Kindness, Robert Wallis, Thomas A. Mitchell, Riccardo Degl’Innocenti, Sergei A. Mikhailov, Harvey E. Beere and David A. Ritchie, April 15, 2022, Science Advances.
DOI: 10.1126 / sciadv.abi8398
The work was supported by the EPSRC project HyperTerahertz (no. EP / P021859 / 1) and grant no. EP / S019383 / 1, Schiff Foundation, University of Cambridge, Trinity College Cambridge, as well as the European Union’s Horizon 2020 Graphene Core 3 research and innovation program (grant number 881603).