This is the first time a highly ordered crystal of bosonic particles called excitons has been created in a real — as opposed to synthetic — matter system.
Subatomic particles come in one of two broad types: fermions and bosons. One of the biggest distinctions is in their behavior.
Bosons can occupy the same energy level; fermions don’t like to stay together. Together, these behaviors construct the Universe as we know it.
Fermions, such as electrons, underlie the matter with which we are most familiar as they are stable and interact through the electrostatic force.
Meanwhile bosons, such as photons, tend to be more difficult to create or manipulate as they are either fleeting or do not interact with each other.
“A clue to their distinct behaviors is in their different quantum mechanical characteristics,” said first author Richen Xiong, a graduate student at the University of California at Santa Barbara.
“Fermions have half-integer spins such as 1/2 or 3/2 etc., while bosons have whole integer spins (1, 2, etc.).”
“An exciton is a state in which a negatively charged electron (fermion) is bound to its positively charged opposite hole (another fermion), with the two half-integer spins together becoming a whole integer, creating a bosonic particle.”
To create and identify excitons in their system, Xiong and colleagues layered the two lattices and shone strong lights on them in a method they call pump-probe spectroscopy.
The combination of particles from each of the lattices (electrons from the tungsten disulfide and the holes from the tungsten diselenide) and the light created a favorable environment for the formation of and interactions between the excitons while allowing the researchers to probe these particles’ behaviors.
“And when these excitons reached a certain density, they could not move anymore,” said senior author Dr. Chenhao Jin, a physicist at the University of California at Santa Barbara.
Thanks to strong interactions, the…
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