Physics discover the most exciting form of matter: Excitonium

NEW MATTER

 The discovery of a new form of matter: excitonium. This material is made up of a kind of boson, a composite particle that could allow the matter to act as a superfluid, superconductor, or even as an insulating electronic crystal.

{Excitonium is a condensate, meaningwhat the researchers detected was a solid. Excitonium is made up of particles called excitons, in the same way that, say, solid aluminum is made up of aluminum particles. The exciton particles themselves, though, aren't created through quite as intuitive a process.}

{Boson : a subatomic particle, such as a photon, which has zero or integral spin and follows the statistical description given by S. N. Bose and Einstein.}

{Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without loss of kinetic energy. When stirred, a superfluid forms cellular vortices that continue to rotate indefinitely.}

Excitonium is a condensate made up of excitons, which are what you get when you combine escaped electrons and the “holes” they left. This quirky quantum-mechanical pairing is possible because, in semiconductors, electrons on the edge of one energy level in an atom are able, when excited, to jump into the next energy level, leaving behind a “hole” in the previous level. This hole acts like a positively charged particle, attracting the negatively charged electron that escaped.

{condensate : liquid collected by condensation.}

{Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently of the others, even when the particles are separated by a large distance—instead, a quantum state must be described .}

To prove the existence of excitons, this team studied crystals doped with dichalcogenide titanium diselenide (1T-TiSe2), a transition metal. They were even able to reproduce their results five separate times.

{dichalcogenide titanium diselenide (1T-TiSe2)

Introduction 

A single molecular layer of titanium diselenide (TiSe₂) is a promising material for advanced electronics beyond graphene—a strong focus of current research. Such molecular layers are at the quantum limit of device miniaturization and can show enhanced electronic effects not realizable in thick films. We show that single-layer TiSe₂ exhibits a charge density wave (CDW) transition at critical temperature T_C=232±5 K, which is higher than the bulk T_C=200±5 K. Angle-resolved photoemission spectroscopy measurements reveal a small absolute bandgap at room temperature, which grows wider with decreasing temperature T below T_C in conjunction with the emergence of (2 × 2) ordering. The results are rationalized in terms of first-principles calculations, symmetry breaking and phonon entropy effects. The observed Bardeen-Cooper-Schrieffer (BCS) behaviour of the gap implies a mean-field CDW order in the single layer and an anisotropic CDW order in the bulk.}

In other words, this was the first-ever observation of a soft plasmon phase that is the precursor to the exciton condensation.

{In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons.}

“This result is of cosmic significance,” Abbamonte stated in a press release. “Ever since the term ‘excitonium’ was coined in the 1960s by Harvard theoretical physicist Bert Halperin, physicists have sought to demonstrate its existence. Theorists have debated whether it would be an insulator, a perfect conductor, or a superfluid — with some convincing arguments on all sides. Since the 1970s, many experimentalists have published evidence of the existence of excitonium, but their findings weren’t definitive proof and could equally have been explained by a conventional structural phase transition.”

Now that excitonium has been proven to exist and has been concretely observed in experimentation, its properties can be further explored and applied. Most obviously, as a superconductor and superfluid, this material could be used to further existing technologies.

Additionally, since analyzing quantum phenomena is what guides and shapes our understanding of quantum mechanics, this research could help to further de-mystify current quantum puzzles.These applications, especially those in practical technologies, are purely speculative at this point, however. It is impossible to exactly predict what the future might hold for excitonium, but we do know for certain that it has more potential now than it ever has before.

 

 The laws of physics themselves start to change if you go down to a small enough scale, with quantum mechanics taking over the more familiar laws of macroscopic physics. A form of matter called a Bose-Einstein condensate (BEC) somewhat bridges the gap between the two. BECs are basically a state of matter in which extremely cold atoms clump up together and behave as a single entity, called a boson. Photons, for instance, are a type of boson, as are some more complex quasiparticles such as plasmons, and phonons.

{A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which point microscopic quantum phenomena, particularly wavefunction interference, become apparent.}

{In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids.}

{Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantization of plasma oscillations, just like phonons are quantizations of mechanical vibrations.}

Excitonium is a type of a condensate made up of excitons — a type of quasiparticles formed in a quantum mechanical pairing from an escaped electron and the hole it left behind. It all starts with a semiconductor, a material with electrical properties somewhere in the middle, between those of a conductor and an insulator. Basically, when an electron on the edge of a semiconductor’s valence band gets excited, it moves on to the conduction side, which is empty. Since all electrons have a negative charge, this leaves behind a “hole” in the valence band, which acts as a positively charged entity. The negative electron and the positive hole are drawn to each other, forming a type of boson called an exciton. The fact that the hole acts as a particle itself can be attributed to the surrounding crowd of electrons. But that understanding makes the pairing no less strange and wonderful.

Excitonium was first proposed half a century ago and was hotly debated by particle physicists. But now, researchers have finally managed to prove its existence and create it. When a largely theoretical particle is proven to also physically exist, the result can only be, well, exciting.