An Insight Into the Fascinating World of Quasiparticles
Tommaso Freschi
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Throughout your high school career you’ve probably heard (or will hear) your science teachers talk about particles, whether that be subatomic particles in chemistry or elementary particles in physics. Also, you probably associate particles with the most commonly used definitions, i.e. “A small portion of something” or “A minute portion of matter”. At the same time, you might also have heard (or will hear) them talk about atoms and compounds in chemistry, and molecules in biology and chemistry.
All these things are what most people would define as what makes up matter, and, don’t get me wrong, they wouldn’t be incorrect in saying that, as it is irrelevant to speak about anything else unless the person reading is a physicist.
Now, I myself am not a physicist, so I do not claim to have the expertise nor the scientific knowledge to fully describe today’s topic (though I will try), nor do I claim that this topic is in any way useful for me to know, but I personally think it is way too interesting and fascinating not to share. So, what is this fascinating topic I keep talking about? Quasiparticles.
According to the Merriam-Webster dictionary, a quasiparticle is defined as “a composite entity (such as a vibration in a solid) that is analogous in its behaviour to a single particle,” though this definition doesn’t do quasiparticles justice, as it makes them seem much less fascinating than they actually are. In order to fully describe what quasiparticles are, I would need to be a physicist, so since I am not, I’m going to borrow an analogy found on the Britannica website. Quasiparticles can be described using an analogy including any fizzy drink, e.g. champagne: the bubbles inside the champagne would not exist without the champagne, but they still have properties of their own, such as size, momentum, etc. The same goes for quasiparticles—they can’t exist outside certain phenomena, but they still have particle-like properties (charge, spin, mass).
Now that I’ve (kind of) explained what quasiparticles are, I would like to share three of my favourite quasiparticles ever: spinons, holons and orbitons.
Before being able to explain those quasiparticles, some background information on elementary particles is needed. All elementary particles (electrons, quarks, photons, etc.) are mainly defined by three properties: mass, charge and spin. For example, an electron would have a mass of 0.511 MeV/c^2 (or 9.109390 x 10^-31 kg), a charge of -1 and a spin of ½. It is also important to note that we are talking about elementary particles here, i.e. non divisible particles—the smallest units of matter that exist.
Representation of the standard model of particle physics, containing all elementary particles.
Now that the background context is out of the way, let’s talk spinons, holons and orbitons. To fully understand these three quasiparticles, we need to consider the electron. The electron, as showcased in the above representation, has three properties as described beforehand. Now, being an elementary particle, the electron isn’t made up of anything, and it has its own properties and can exist by itself without the need of certain phenomena to exist, so it can be described as a particle. But something really peculiar can be seen happening to electrons when the temperature is lowered to close to 0K (absolute zero—the coldest possible temperature in the universe, which is impossible to reach) and they are put very close together.
When many electrons are brought close to absolute zero and are packed very tightly together, three new quasiparticles can be identified: spinons, holons and orbitons. Now what’s interesting about these is that, like I said, they are quasiparticles, and, therefore, cannot exist on their own, so don’t confuse them for particles that make up the electron, as it is still elementary and fundamental. However, they still carry certain properties of the electron: the spinon carrying the spin of the electron, the holon carrying the charge of the electron and the orbiton carrying the orbital location of the electron (function describing both the location and the behaviour of an electron in an atom).
These three quasiparticles cannot exist outside of the very specific criteria defined above, which is why they cannot be defined as particles, but their existence alone is enough to blow many people’s minds—mine included.
These are only three of the many quasiparticles (even though they win the trophy of being my favourite) and I just scratched the surface even with holons, spinons and orbitons, so I would suggest everyone interested in physics look into the other quasiparticles, as their world is fascinating and vast.
References:
Britannica, T. Editors of Encyclopaedia (2018, May 23). quasiparticle. Encyclopedia Britannica. https://www.britannica.com/science/quasiparticle
Merali, Z. (2012, April 18). Not-quite-so elementary, my dear electron.
https://www.nature.com/articles/nature.2012.10471
Wikimedia Foundation. (2022, February 9). Holon (physics). Wikipedia.
https://en.wikipedia.org/wiki/Holon_(physics)
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