Ultrafast switching of trions in 2D materials achieved with terahertz photons
by Robert Schreiber
Berlin, Germany (SPX) Sep 30, 2024
An international team led by researchers from TU Dresden has successfully demonstrated an extremely fast switching process between electrically neutral and charged luminescent particles within ultra-thin materials consisting of just a few atomic layers. This important breakthrough, achieved through experiments at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), promises new avenues for optical data processing and sensor technology applications. The results were published in ‘Nature Photonics’ (Venanzi and Cuccu et al., DOI: 10.1038/s41566-024-01512-0).
Two-dimensional semiconductors, unlike bulk crystals, exhibit unique properties that make it easier to generate exciton particles – pairs formed when a negatively charged electron and a positively charged “hole” combine. Under certain conditions, these excitons can capture an additional electron to form a trion, a state that combines electrical charge with strong light emission, enabling simultaneous optical and electronic control.
For years, scientists have explored the interplay between excitons and trions as a potential switching process for future technological applications. However, the speed of switching between these states had been limited – until now. The research team, led by Prof. Alexey Chernikov from TU Dresden and HZDR’s Dr. Stephan Winnerl, managed to accelerate this process significantly using terahertz radiation.
The experiments employed the FELBE free-electron laser at HZDR, which emits terahertz pulses, a frequency range between radio waves and near-infrared radiation. The researchers first illuminated a thin layer of molybdenum diselenide with laser pulses at cryogenic temperatures, creating excitons. These excitons quickly captured nearby electrons, forming trions. By then exposing the material to terahertz pulses, the trions rapidly converted back into excitons.
“When we then shot terahertz pulses at the material, the trions formed back into excitons extremely quickly,” explains Winnerl. “We were able to show it because excitons and trions emitted near-infrared radiation at different wavelengths.” This process took place in a matter of picoseconds – trillionths of a second – nearly a thousand times faster than previously achieved through electronic methods.
The next phase of this research could extend these processes to various electronic states and material platforms, potentially advancing the development of room-temperature applications. In the future, this method could be adapted for use in fast-switching modulators and compact optical data processing components.
The results also hold promise for sensor technology. Dr. Winnerl noted that this could lead to the development of detectors that operate in the terahertz range and might even pave the way for terahertz cameras capable of capturing detailed images at these frequencies. According to Prof. Chernikov, “In principle, even a comparatively low intensity should be sufficient to trigger the switching process.” The team envisions further technological advancements as this discovery opens the door to detecting near-infrared light changes in materials, using already existing technology.
Research Report:Ultrafast switching of trions in 2D materials by terahertz photons
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