Physicists solve the mystery of vanishing particles in graphene

phys.org | 6/19/2018 | Staff
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Researchers from the Moscow Institute of Physics and Technology and Tohoku University (Japan) have explained the puzzling phenomenon of particle-antiparticle annihilation in graphene, recognized by specialists as Auger recombination. Although persistently observed in experiments, it was for a long time thought to be prohibited by the fundamental physical laws of energy and momentum conservation. The theoretical explanation of this process has until recently remained one of the greatest puzzles of solid-state physics. The theory explaining the phenomenon was published in Physical Review B.

In 1928, Paul Dirac predicted that an electron has a twin particle, which is identical in all respects but for its opposite electric charge. This particle, called the positron, was soon discovered experimentally. Several years later, scientists realized that the charge carriers in semiconductors—silicon, germanium, gallium arsenide, etc.—behave like electrons and positrons. These two kinds of charge carriers in semiconductors were called electrons and holes. Their respective charges are negative and positive, and they can recombine, or annihilate each other, releasing energy. Electron-hole recombination accompanied by the emission of light provides the operating principle of semiconductor lasers, which are devices crucial for optoelectronics.

Emission - Light - Outcome - Electron - Contact

The emission of light is not the only possible outcome of an electron coming in contact with a hole in a semiconductor. The liberated energy is often lost to thermal vibrations of the neighboring atoms or picked up by other electrons (figure 1). The latter process is referred to as Auger recombination and is the main "killer" of active electron-hole pairs in lasers. It bears the name of French physicist Pierre Auger, who studied these processes. Laser engineers strive to maximize the probability of light emission upon electron-hole recombination and to suppress all the other processes.

Thus, the optoelectronics community enthusiastically greeted the proposal for graphene-based semiconductor lasers formulated by MIPT graduate Victor Ryzhii. The initial theoretical...
(Excerpt) Read more at: phys.org
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