Researchers have found evidence of cooperation in the unlikeliest of places — among atoms within solids.
Alexey Belyanin, professor of physics at Texas A&M University, and Belyanin research group members Yongrui Wang and Aleksander Wojcik are part of a team of scientists that first predicted and recently observed this effect, known as superfluorescence, in solid-state materials — in this case, electron-hole pairs created in a semiconductor using lasers. Their results are featured in a recent issue of the journal “Nature Physics,” viewable at the following link: http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys2207.html
“We predicted the possibility of this self-organization and collective recombination in semiconductors a long time ago, but nobody was able to observe it,” Belyanin says. “We also pointed out at that time that you might get a better chance of observing superfluorescence if you have a layered semiconductor (so-called quantum wells) and impose a strong magnetic field to prevent electrons from bumping into each other too often and to increase their coupling to light. We are happy that our collaborators Dr. Junichiro Kono and his group from Rice University were able to test these ideas and observe the effect.”
Belyanin says superfluorescence is a rare phenomenon — one almost counterintuitive in semiconductors — that can only happen when “many bodies” decide to work together. He credits his Rice colleagues for conducting a meticulous and difficult experiment that required a strong magnetic field and low temperatures obtained at Florida State University’s National High Magnetic Field Laboratory in collaboration with physicists at the University of Florida to prove it.
“It took several years to plan everything and get the data,” the Texas A&M professor adds. “The Rice group did it beautifully, and I think that the results are absolutely convincing.”
Belyanin says the true beauty of the experiment lies in the after-effects of that powerful femtosecond laser pulse, which near-instantaneously creates a huge number of free electrons that bump into each other and into the atoms of a crystal. But instead of gradually losing their energies and eventually disappearing in the course of a few nanoseconds, thereby returning the crystal back to equilibrium, he says they rally together to emit a giant and extremely short burst of light that consumes all particles within a few picoseconds.
For more information, go to http://www.science.tamu.edu/articles/866.