Beyond familiar particles like electrons and protons, scientists have discovered a zoo of “quasiparticles” that have exotic names, such as magnon, angulon, dropleton, and polariton. But what exactly are quasiparticles? And given “semi” in their name, are they considered true particles?
One way to understand quasiparticles is to figure out what a particle is. The standard mental picture of a particle is “of an isolated object like a ball,” Douglas Natelsona condensed matter physicist at Rice University in Houston told Live Science. However, this classic image of particles changed with the advent of quantum physicsWhich showed that the universe becomes vague at its smallest level. For example, in 1924, the French physicist Louis de Broglie showed that Particles like electrons can also behave like waves – a discovery that earned him nobel prize.
Modern physics Suggests that particles are excitations in fields that pervade the entire universe, like ripples in a pond, Ross McKenziea theoretical condensed matter physicist and professor emeritus at the University of Queensland in Australia, told Live Science. Each type of particle has its own corresponding field. For example, photons of light are waves electromagnetic fieldsMcKenzie said.
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The quantum nature of the particles means that they can not only fly through an empty vacuum but also ripple through matter. For example, photons can zip through transparent and translucent materials, and electrons can flow inside wires.
If you can picture a standard particle, such as an electron, as a wave traveling within a material, you can also imagine other types of excitations within the material. These other types of waves are quasiparticles.
For example, think of the “wave” done at a sporting event. Natelson said, “You can see it spread around a football stadium; it has a space and a pace.” “However, it only exists within the stadium, and it is created by the collective reaction of all the fans interacting.”
In much the same way, “quasiparticles can only exist within a medium or material because they are created by the reaction of components or building blocks of that material,” Netelson said; In contrast, particles such as the electron and proton “can exist in free space.”
Electrons have a negative charge and revolve around the nucleus of the atom.
(Image credit: Agung Fatriya via Getty Images)
In other words, quasiparticles cannot exist in a vacuum and they cannot exist on their own. They depend on particles working together and being in a material where they can emerge, just as a wave in a stadium can only exist if there is a group of people who can execute it.
A philosophical question related to quasiparticles is whether they are real, McKenzie said. After all, “quasi” means “almost” in Latin.
“Fundamental particles can exist in isolation in a vacuum, and quasiparticles require many interacting particles to exist,” McKenzie said. “Still, I would say that quasiparticles are, for all intents and purposes, just as real as particles in terms of how you can detect and manipulate them.”
a zoo of semiconductors
The concept of quasiparticles originated with theoretical physicist Lev Landau in the 1950s, McKenzie said, and the idea ultimately helped Landau win over. Nobel Prize in Physics 1962. Scientists have now proposed the existence of dozens of quasiparticle types, including the following:
McKenzie said the phonon, which is a quasiparticle of sound — is the smallest packet of vibrational energy that creates sound in matter.
McKenzie said that the electron hole, often simply called a hole, is a positively charged vacancy left after an electron leaves its original position.
Electron quasiparticle, which essentially consists of an electron and its interaction with its surrounding environment. McKenzie explained that this combined package means that the electron quasiparticle requires more force to move, so it effectively has more mass than a regular electron.
Exciton, a quasiparticle composed of an electron and a hole orbiting each other.
Anion, a type of semiparticle that has so far only been observed in two-dimensional systems, can carry only a fraction of the electrical charge.
“How many types of semiconductors are there?” McKenzie said. “Just as there are an infinite number of possible states of matter, I would say that, in principle, there are also an infinite number of types of quasiparticles.”
Scientists describe activity in materials as quasiparticles “because it simplifies everything so dramatically,” McKenzie said. Similarly, Netelson stated that “the mathematics behind physical phenomena in solids is often well described by quasiparticles.”
Quasiparticles aren’t just useful for bookkeeping. For example, researchers typically describe the behavior of electricity in electronic devices in terms of quasiparticles such as holes and excitons, Nettleson said.
Overall, the answer to the question whether quasiparticles are real is a matter of interpretation. If the question is whether the quasiparticle is one or not elementary particles As for an electron, the answer is no – they cannot exist on their own, and depend on the materials in which they appear.
However, if the question is whether quasiparticles are real phenomena, the answer is yes – they are things that scientists can measure that behave like particles and effectively have the same properties that other particles have.
