Particles* I work with as a theoretical chemist, from most typical to wildest:
Proton - Positive vibes, pretty quarky. A classic.
Neutron - Like the proton, but neutral. Sometimes simplicity is best.
Electron - Less than 1/1000th the mass of our first 2 particles. Less mass means more quantum weirdness, which means more fun. At this point, wave-like behavior is becoming pretty significant.
Atom - A particle created from the combination of a nucleus of protons and neutrons and orbiting electrons, atoms are a chemist’s bread and butter. Otherwise, these are pretty straightforward. For simplicity, I’ll be excluding ions from this list, as they’re just atoms either with more or less electrons than they’re supposed to have.
Molecules - Created from several atoms bonded together by shared electrons, molecules are like atoms, but a little more complicated. They can rotate, vibrate, and much more. Molecules can have anywhere from 2 atoms to millions, and it’s molecules that describe most chemical systems.
Photon - The particle form of light. Photons are massless packets of energy that can be freely created or destroyed. This is about the point where things are really getting weird. Let’s see how.
Phonon* - The particle form of lattice vibrations. In a solid, vibrations of individual molecules are not independent of each other; however, these collective vibrations can be separated into a series of fixed patterns with their own energies. Those patterns can then be treated as particles in their own right, creating a “gas” of phonons. At this point, the particle definition is getting stretched quite a bit, but to deal with a system like this, this particle treatment works quite well to simplify the math and make it reasonable to deal with the system.
Hole* - One of the few of these that doesn’t end in “-on”, the hole represents an empty space where an electron should be on a material’s surface. The remaining particles on this list, much like the phonon, are designed to deal with solids in a convenient way. In this case, because the surface is made up of positively charged nuclei with negatively charged electrons on top, removing the electron leaves a positively charged space behind. Turns out, we can say this hole behaves like a particle itself, which moves as electrons shift across the surface. It should also be noted that electrons on a surface are treated differently than in free space, so one could argue that a surface electron is also its own kind of particle*.
Exciton* - We’ve seen that pairing a nucleus and electrons creates an atom, but what if we try to create the surface equivalent? Normally, putting an electron where a hole is would just move the hole, but what if we were to excite the electron so that it orbits around the hole? These are excitons. Excited, neutrally charged hydrogen-like particles on the surface of a solid. This is what my research focuses on.
Plasmon* - As our final particle, we’ll briefly talk about plasmons. I don’t know these particles too well, but from discussion with some colleagues who work with them, a plasmon is the particle form of oscillating electrons either on a surface or in a plasma. These are notably rather similar to phonons, in that we’re just treating the movement of many electrons by dividing them into collective states that we can treat as particles. At this point, the definition of a particle has been stretched pretty well beyond the typical limit, but for these kinds of system, mathematical convenience is beyond just desirable. It’s essential.
This list is not a list of every possible particle or quasiparticle. I’ve omitted antimatter, quarks, and many elementary particles in the standard model on one end, and on the quasiparticle end, I’ve omitted things like polarons (excitons + phonons) and polaritons (excitons/plasmons/phonons + photons). Maybe I’ll discuss these at another point, but there is still much I would like to learn about these kinds of systems. Either way, until next time, byyyyyyeeeeeee.
*Not all of these are “particles” in the traditional sense. Several are just mathematical constructs designed to turn complicated systems into easy things we know. In such cases, one could refer to these as quasiparticles, which can behave like particles well enough for us to model them as such. For clarity, I’ll try to mark all quasiparticles with an asterisk.
