Tuesday, March 3, 2009
After class today, I was directed to see the Mensa-smart link to talk by Melinda Kellogg called
"Stalking the Exciton Condensate: Exotic Behavior of Electrons under Extreme Conditions"
I had to see what this is about so I looked it up and found the Wiki definition the simplest:
An exciton is a bound state of an electron and an imaginary particle called an electron hole in an insulator or semiconductor, and such is a Coulomb-correlated electron-hole pair. It is an elementary excitation, or a quasiparticle of a solid. In current research, the bound electron and hole pairs (excitons) provide a means to transport energy without transporting net charge.
"What is coherence and why is it so important?" asks Leonid Butov, a professor of physics at UCSD. "To start with, modern physics was born by the discovery that all particles in nature are also waves. Coherence means that such waves are all 'in sync.' The spontaneous coherence of the matter waves is the reason behind some of the most exciting phenomena in nature such as superconductivity and lasing."
"A simple way to visualize coherence is to imagine cheering spectators at a stadium making 'a wave'," added Michael Fogler, an assistant professor of physics at UCSD and a co-author of the paper. "If the top rows get up and down at the same time as the bottom ones, the rows are mutually coherent. In turn, coherence is spontaneous when the cheering is done on the spectator's own initiative and is not orchestrated by the directions of an external announcer."
A famous example of spontaneous coherence of matter waves is the Bose-Einstein condensate, which is a state predicted by Einstein some 80 years ago. This new form of matter was eventually created in 1995 by University of Colorado physicists and regarded as so noteworthy the scientists were awarded the 2001 Nobel Prize in Physics. The Bose-Einstein condensate is a gas of atoms so dense and cold that their matter waves lose their individuality and condense into a "macroscopic coherent superatom wave."
Besides advances in computing, materials science and semiconducntors, I find fascinating the state of matter described as just becoming solid as waves of energy-matter synchronize and settle into solid.