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Sunday, 23 June 2019

Physicists discover exotic spiraling electrons

The two types of "chiral surface excitons" are on the right and left sides of the image. They are generated by polarized light to the right and left (photons in blue). Excitons consist of an electron (light blue) orbiting a gap (black) in the same orientation of light. The electron and the gap are annihilated in less than a trillionth of a second, emitting light (photons in green) that can be harnessed for illumination, solar cells, lasers and screens [Hsiang-Hsi Kung / Rutgers]

Surface chiral exciton

Physicists have discovered an exotic form of electron that can lead to advances in lighting, solar cells, lasers and electronic screens.

Spinning like planets, these electrons consist of particles and "antiparticles" orbiting around one another on the surface of solid materials - not antimatter, but particles with opposing charges.

These exotic particles - or quasiparticles - were termed "surface chiral excitons."

Excitons form when intense light strikes a solid, kicking electrons negatively charged from their positions and leaving behind positively charged gaps - ejected electrons form surface plasmons , another quasiparticle of great technological interest.

Chiral refers to entities, such as their right and left hands, which correspond, but are asymmetrical, and can not be superimposed on their mirror image. The chirality of the new quasiparticle depends on the polarization of the light that produces it.

The electrons and gaps generated in this process resemble fast spinning rods. Electrons (negative charges) eventually "spiral" into gaps (positive charges), annihilating each other in less than a trillionth of a second, which results in the emission of a type of light called photoluminescence .

Photoluminescence is involved in numerous technological applications, such as solar cells, lasers, LEDs, screens, etc. Thus, the controlled production of light by the production of surface chiral excitons may eventually be exploited in all such devices.

Bismuth selenide

Hsiang-Hsi Kung and his colleagues at Rutgers University in the United States have discovered the chiral excitons on the surface of a crystal called bismuth selenide, which can be produced on a large scale and used in coatings and other materials in electronics - all at room temperature.

This crystal had already been used to synthesize a bizarre substance that unifies spintronics and quantum computing . And, on its surface, was also discovered, in 2013, a then unprecedented coupling between photon and electron, uniting matter and energy .

"Bismuth selenide is a fascinating compound that belongs to a family of quantum materials called ' topological insulation .' They have several surface channels that are highly efficient in conducting electricity," said Professor Girsh Blumberg.

The dynamics of chiral excitons is still unclear and the team plans to use ultrafast images to study it in depth. They also evaluate that surface chiral excitons can be found in other materials.




Bibliography:

 Observation of chiral surface excitons in a topological insulator Bi2Se3
Hsiang-Hsi Kung, Adamya P. Goyal, Dmitrii L. Maslov, Xueyun Wang, Alexander Lee, Alexander F. Kemper, Sang-Wook Cheong, Girsh Blumberg
 Proceedings of the National Academy of Sciences
 DOI: 10.1073 / pnas.1813514116

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