We Just Discovered an Entirely New Form of Matter

Monday, 11 December 2017 - 10:10AM
Weird Science
Monday, 11 December 2017 - 10:10AM
We Just Discovered an Entirely New Form of Matter
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When it comes to scientific discoveries, kids of the future have it rough.

Right now, students have to memorize three or four states of matter: solid, liquid, gas, and (maybe) plasma.

Then there are Bose-Einstein Condensates, which are a weird state of matter that can happen when you cool down certain types of elements and subject them to lasers and magnets...and stuff.

Now there's excitonium, which is a type of condensate.

Needless to say, it's also weird one.

To wrap our heads around excitonium, let's first travel back in time to those high school classes (which are about to become much more complicated).

Atoms can have a number of different 'bands' of electrons around them, usually depicted in concentric circles, with lower-energy bands closer to the atom and higher-energy bands farther out. Every band can hold a certain number of electrons, with extra electrons being pushed into a 'higher' band.

The highest band that has electrons in it is called the valence band. There's an even higher band, however, called the conduction band, which takes a lot of energy for electrons to cross into (it's also the band that allows electrical conductivity). 

With all that in mind, it's time to get weird.

"It defies reason, but it turns out that when an electron, seated at the edge of a crowded-with-electrons valence band in a semiconductor, gets excited and jumps over the energy gap to the otherwise empty conduction band, it leaves behind a "hole" in the valence band," researchers explained.

"That hole behaves as though it were a particle with positive charge, and it attracts the escaped electron. When the escaped electron with its negative charge, pairs up with the hole, the two remarkably form a composite particle, a boson—an exciton."
Though excitons have been observed before, scientists chased excitonium for 50 years before finding evidence that all those weird excitons could indeed form a new type of matter.

Now, thanks to Peter Abbamonte and graduate students Anshul Kogar and Mindy Rak at the University of Illinois, the "smoking gun" has been discovered that proves excitonium is real.

As a condensate, it exhibits "macroscopic quantum phenomena"—meaning that all the strange little quantum effects that are normally observed at the atomic level are shown working on a much larger scale.

Figuring out how quantum phenomena guide physics on larger scales is one of the mysteries of modern science.

The theory of relativity works great, but then a whole new set of rules seems to kick in around the atomic level—quantum physics.

Understanding how the two relate (as well as the boundary between them) could lead to a new, unified theory of everything, and excitonium is one more piece of the puzzle.
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We Just Discovered an Entirely New Form of Matter