The breakthrough brings us one step closer to the real terahertz technologies

Scientists have discovered a new effect in two-dimensional conduction systems, which promises improved performance of terahertz detectors.

The recent discovery of physics in two-dimensional conductive systems allows for a new type of terahertz detector. The terahertz frequencies between microwave and infrared in the electromagnetic spectrum could allow for faster, safer, and more efficient imaging technologies, as well as much higher speeds for wireless telecommunications. The lack of efficient real-world devices hinders these developments, 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.

To begin with, what are terahertz waves? “We communicate with mobile phones that transmit microwave radiation and use infrared cameras for night vision. Terahertz is the type of electromagnetic radiation that lies between microwave and infrared radiation, “said Professor David Richie, head of the semiconductor physics group at the Cavendish Laboratory at the University of Cambridge. 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 in Italy, were the first to demonstrate in 2002 the action of a terahertz laser, a quantum cascade laser. Since then, the group has continued to study terahertz physics and technology and is currently researching and developing functional terahertz devices, including metamaterials for modulator formation, as well as new types of detectors.

Vladislav Mihailov shows a device in a clean room and a terahertz detector after production. Credit: Vladislav Mikhailov

If the lack of usable devices is decided, terahertz radiation can have many useful applications in security, materials science, communications and medicine. For example, terahertz waves allow the depiction of cancerous tissue that cannot be seen with the naked eye. They can be used in new generations of safe and fast airport scanners, which make it possible to distinguish drugs from illicit drugs and explosives, and can be used to provide even faster wireless communications beyond the latest.

So what is the recent discovery about? “We were developing a new type of terahertz detector,” said Dr. Vladislav Mihailou, a junior researcher at Trinity College Cambridge, “but when we measured its performance, it turned out to be much stronger than expected.” So 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 single particles – photons. This interpretation, first proposed by Einstein, forms the basis of quantum mechanics and is able to explain the photoelectric effect. This quantum photoexcitation is the way light is detected by the cameras in our smartphones; it also generates electricity from light in solar cells.

The well-known photoelectric effect consists in the release of electrons from a conductive material – metal or semiconductor – from incident photons. In the three-dimensional case, the electrons can be expelled in a vacuum by photons in the ultraviolet or X-ray range or released into a dielectric in the middle infrared to visible range. The novelty is in the discovery of a process of quantum photoexcitation in the terahertz range, similar to the photoelectric effect. “The fact that such effects can exist within high-conductivity, two-dimensional electron gases at much lower frequencies has not yet been understood,” explains Vladislav, the study’s first author, “but we have been able to prove this experimentally.” The quantitative theory of the effect was developed by a colleague from the University of Augsburg, Germany, and an international team of researchers recently published their findings in the renowned journal Scientific achievements.

Researchers have called the phenomenon a “photoelectric effect in the plane.” In the corresponding article, scientists describe several benefits of using this effect to detect terahertz. In particular, the magnitude of the photo-response generated by the falling terahertz radiation from the “photoelectric effect in the plane” is much higher than expected from other mechanisms that have hitherto been known to lead to a terahertz photo-response. Thus, scientists expect that this effect will allow 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 Prof. Richie.

Reference: “Photoelectric effect in the plane in two-dimensional electronic systems for terahertz detection” by Vladislav Mihailou, Peter Spencer, Nikita W. Almond, Stephen J. Kindness, Robert Wallis, Thomas A. Mitchell, Ricardo Degl’Inocenti, Sergei A. Mikhailov, Harvey E. Beer and David A. Richie, April 15, 2022, Scientific achievements.
DOI: 10.1126 / sciadv.abi8398

The work was supported by EPSRC projects HyperTerahertz (№ EP / P021859 / 1) and grant (. EP / S019383 / 1, Schiff Foundation, University of Cambridge, Trinity College Cambridge, and the European Union’s Horizon 2020 Graphene Core 3 research and innovation program (grant № 881603).