The discovery heralds from the University of Illinois College of Engineering. The new form of matter is easiest described as collective excitons of an excitonic solid, a state which accounts for the name – excitonium. The discovery is not just of academic interest. Excitonium is a condensate, which allows for it to demonstrate macroscopic quantum phenomena, much like a superconductor, superfluid, or insulating electronic crystal.
The particles that make up the material – excitons – particles that are formed in an unusal quantum mechanical pairing, made up of an escaped electron together with the hole the electron leaves behind. Electrons leave when they become excited, which causes the electron to pass through an energy gap. The resultant hole unusually behaves as if it was a positively charged particle. The positive charge acts to pull the escaped negatively charged electron back. Here the two pair up and form a composition boson particles – the exciton.
A series of exictions influences the collective behavior of the surrounding crowd of electrons. In terms of being a boson, these are particles that have a whole number spin and which carry energy.
The serendipitous discovery came about after physicists were studying non-doped crystals of the transition metal dichalcogenide titanium diselenide (1T-TiSe2), which is an inorganic compound of titanium and selenium. The material is often studied because it possesses properties of potential value in battery technology. On discovering the matter the researchers successfully reproduced their findings five times on different cleaved crystals.
The technique used for the discovery is called momentum-resolved electron energy-loss spectroscopy, in a transmission electron microscope. The technique is novel and more sensitive than X-rays.
The significance of the discovery could one day advance electronics, due to the powerful insulating properties of the exciton. The discovery has been published in the journal Science. The research paper is titled “Signatures of exciton condensation in a transition metal dichalcogenide.”
