Scientists implement reverse Cherenkov radiation in the infrared band

In order to construct an optoelectronic integrated circuit based on polaritons, it is urgent to develop a nanolight source that can be integrated on chip as an information input port. “Reverse Cherenkov radiation” has the characteristics of the opposite direction of movement of charged particles and the direction of electromagnetic radiation, which can effectively shield the interference of moving particles with radiated electromagnetic waves, thereby significantly improving the quality of nanolight sources.

On May 3, Dai Qing’s research team at the National Center for Nanoscience published a paper in Nature Communications reporting the phenomenon of phonon polarizon reverse Cherenkov radiation observed in the natural molybdenum I hyperbolic band.

Yang Xiaoxia, co-corresponding author of the paper, said that it has been reported in the early stage to obtain reverse Cherenkov radiation in the microwave frequency band in metamaterials, but with the increase of frequency, the electromagnetic loss of the structure increases exponentially, and how to obtain reverse Cherenkov radiation in the infrared band is still a difficult challenge.

To obtain reverse Cherenkov radiation in the infrared band, the research team shifted their attention from the metamaterial to natural crystals. They believe that unlike the idea of obtaining negative refractive index through spatial structure design in the above-mentioned metamaterials, the polarion mode with negative group velocity dispersion in natural crystals is also expected to achieve reverse Cherenkov radiation. This method of obtaining reverse Cherenkov radiation in the infrared frequency band using natural crystals can avoid electromagnetic losses caused by micro-nanostructure fabrication technology.

Dai Qing introduced that in recent years, he led the research team to use the characteristic electron excited polarion theoretical model and experimental characterization method to find phonon polarizon with hyperbolic dispersion in birefringence crystals (such as hexagonal boron nitride and molybdenum oxide and other van der Waals materials). “On the one hand, this hyperbolic phonon polarizon has a negative group velocity in the mid-infrared band, which provides the necessary conditions for the realization of reverse Cherenkov radiation, and on the other hand, it has a significant slow light effect, which is conducive to reducing the threshold of charged particle velocity required to excite radiation.” He said.

In the newly published work, the research team observed phonon polarion reverse Cherenkov radiation on the natural molybdenum I type hyperbolic frequency band, that is, the plasmon polarization excitation (charged particles of analog motion) of the metal antenna to excite phonon polarizon reverse Cherenkov radiation.

The study found that by changing the direction of motion of charged particles, the distribution of reverse Cherenkov radiation could be reshaped asymmetrically. In addition, the construction of molybdenum oxide and hexagonal boron nitride van der Waals heterojunctions by atomic manufacturing technology can further regulate the radiation angle and quality factor, thereby improving the quality of nanolight sources.

The researchers expect that this research result is expected to provide a new idea for solving the problem of efficient excitation of optical band reverse Cherenkov radiation, and provide an important material platform for the realization of on-chip light sources in optoelectronic integrated circuits.

Researcher Dai Qing and Yang Xiaoxia of the National Center for Nanoscience are the co-corresponding authors of the paper, and Guo Xiangdong, special research assistant of the National Center for Nanoscience, and Wu Chenchen, a 2018 doctoral student, are co-authors. (Source: China Science News Gan Xiao)

Schematic diagram of polarion reverse Cherenkov radiation (photo courtesy of the research team)

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