What are quasiparticles exactly?
In: Physics
Imagine a bubble under water, moving around. We can examine the motion of this bubble as its own thing and look at the behavior of the bubble itself.
When we do this what we’re actually studying is how the water moves around to accommodate a hole in the water. In doing so we can do things like considering how a hole in the water responds to gravity (it moves opposite gravity, as if it had negative weight). This analogy isn’t perfect since the hole is filled with air, but it sets the stage for turning to particle physics.
If you look at certain materials there’s a lot of electrons moving around, giving a more or less uniform sea of electrons. Analyzing the motion of all of the electrons is complicated, but you can instead look at the places where an electron *isn’t*. That “lack of electron” can be treated as if it were a particle in and of itself. That imagined particle can be assigned values that real particles have, but these values don’t necessarily have to follow normal rules. For example, an electron hole may be analyzed as a particle with negative mass, despite mass always being positive for real particles.
Electron holes are the most commonly considered quasiparticles since they’re a simple way to reason about semiconductors, but other quasiparticles arise when looking at other things like crystals or magnets.
This is all just an analysis technique to make complex systems easier to deal with. Quasiparticles aren’t “real,” despite being a useful tool to describe real phenomena. If you were to analyze the system by considering all the real particles you’d wind up at the same result, just with much greater effort to get there.
They are collections of field excitations that correspond to the excitations a particle would cause. Generally, they are just particles, once you get over the “particles ought to be conserved” concept of non-quantum physics.
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