Physics Breakthrough: New Form of Matter Discovered Called “Excitonium”

A form of matter that was perplexed scientists for over 50 years has been proven to exist. This makes six known states of matter now: liquids, gases, solids, plasma, Einstein-Bose condensates, and “excitonium.”

Back in most folks school days, they were taught that only four states of matter existed. Though plasma was discovered in 1879, most of us didn’t research it as part of our general course material. Then we were introduced to the Einstein-Bose condensate, which was introduced in the 1920s. Now we’ve got a new verifiable state of matter, and it gets even more interesting than the Boson.

Excitonium is the name of a state of matter coined by the Harvard theoretical physicist, Bertran (Bert) Halperin. “It’s as close to ‘proved’ as you’re ever going to get in science,” Peter Abbamonte, a physics professor at the University of Illinois at Urbana-Champaign, said, “You can never really ‘prove’ anything, but, well, people find it convincing.”

Abbamonte is the physicist responsible for the discovery, who shared excitement over the find with Halperin whom he saw at a party.

Abbamonte and researchers from the University of California and University of Illinois studied crystals of a transition metal— dichalcogenide titanium diselenide (1T-TiSe2). They discovered excitonium while observing the non-doped crystals under a powerful microscope. The “new” form of matter exhibits quantum phenomena, like a superconductor, with particles that a formed in a strange, quantum mechanical dance.

Though researchers have tried locating this form of matter for several decades, they could not locate it, because they did not have the correct experimental tools. However, with a novel new approach, they were able to distinguish excitonium from the Peierls phase, which is completely unrelated to excitonium formation.

Peierls phases and exciton condensation share the same symmetry and similar observables — a superlattice and the opening of a single-particle energy gap.

However, Abbamonte and his team were able to overcome that challenge of deciphering the difference with momentum-resolved electron energy-loss spectroscopy (M-EELS). M-EELS is more sensitive to valence band excitations than inelastic x-ray or neutron scattering techniques.

Kogar retrofit an EEL spectrometer, which on its own could measure only the trajectory of an electron, giving how much energy and momentum it lost, with a goniometer, which allowed the team to measure very precisely an electron’s momentum in real space.

Science Daily explains what excitonium is,

Excitonium is a condensate — it exhibits macroscopic quantum phenomena, like a superconductor, or superfluid, or insulating electronic crystal. It’s 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.”

The discovery, scientists say, has cosmological implications. The scientists who have studied this new state of matter argue that it holds great promise for unlocking further quantum mechanical mysteries: after all, the study of macroscopic quantum phenomena is what has shaped our understanding of quantum mechanics. It could also shed light on the metal-insulator transition in band solids, in which exciton condensation is believed to play a part. Beyond that, possible technological applications of excitonium are purely speculative.

So – a new quantum mechanical particle could alter the way we create and use matter. In a nutshell, the world just realized quantum possibilities for its own technological and cosmological advancement.  

Image: Times of India

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