Annihilation With Spiraling Electrons

Chiral surface excitons are generated by right- and left-handed light. The excitons consist of an electron orbiting a hole in the same orientation as the light. The electron and hole are annihilated in less than a trillionth of a second, emitting light that could be harnessed for lighting, solar cells, lasers and electronic displays. (Source: H.-H. Kung, Rutgers U.)

Physicists from Rutgers University and colleagues have discovered an exotic form of electrons that spin like planets and could lead to advances in lighting, solar cells, lasers and elec­tronic displays. The “chiral surface exciton” consists of particles and anti-particles bound together and swirling around each other on the surface of solids.

Excitons form when intense light shines on solids, kicking negatively charged electrons out of their spots and leaving behind positively charged holes, according to Hsiang-Hsi (Sean) Kung, a graduate student in the Laser Spectro­scopy Lab at Rutgers University. The electrons and holes resemble rapidly spinning tops. The electrons even­tually spiral towards the holes, anni­hilating each other in less than a trillionth of a second while emitting light by photo­luminescence. This finding has appli­cations for devices such as solar cells, lasers and TV and other displays.

The scientists discovered chiral excitons on the surface of a bismuth selenide crystal, which could be mass-produced and used in coatings and other materials in electronics at room tempera­ture. “Bismuth selenide is a fasci­nating compound that belongs to a family of topo­logical insulators,” said Blumberg, a professor in the Department of Physics and Astro­nomy in the School of Arts and Sciences. “They have several channels on the surface that are highly efficient in conducting elec­tricity.”

The dynamics of chiral excitons are not yet clear and the scientists want to use ultra-fast imaging to further study them. Chiral surface excitons may be found on other materials as well. (Source: Rutgers U.)

Reference: H.-H. Kung et al.: Observation of chiral surface excitons in a topological insulator Bi2Se3, Proc. Nat. Ac. Sc., online 20 February 2019; DOI: 10.1073/pnas.1813514116

Link: Girsh Blumberg’s Rutgers Laser Spectroscopy Lab, Rutgers University, New Brunswick, USA

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