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Scientists discover new form of matter: 'Excitonium'

Los Angeles: Scientists have proven the existence of new form of matter called excitonium, which was first theorised almost 50 years ago. Researchers from University of California Berkeley and University of Illinois at Urbana-Champaign in the USA studied non-doped crystals of the transition metal dichalcogenide titanium diselenide (1T-TiSe2).

Excitonium is a condensate — it exhibits macroscopic quantum phenomena, like a superconductor. It is made up of excitons, particles that are formed in a very strange quantum mechanical pairing, namely that of an escaped electron and the hole it left behind.
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. 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. In point of fact, the hole's particle-like attributes are due to the collective behaviour of the surrounding crowd of electrons. However, that understanding makes the pairing no less strange and wonderful, researchers said.
Until now, scientists have not had experimental tools to positively distinguish whether what looked like excitonium was not in fact a Peierls phase. Peierls phases and exciton condensation share the same symmetry and similar observables.

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