New quasi-particle discovered: Introducing the Pi-ton
phys.org
phys.org
That's precisely how my physics professor in 11th grade explained to us how PNP transistors works, more then 25 years ago
It is also known that and electron and a hole can be bound and form an "exciton" that is stable enough to be called a quasiparticle. It's somewhat similar to positronium. [1]
The novel part of the article is that (in some materials?) two electrons and two holes can bound together and form something that is stable enough to be called a quasiparticle.
[1] Why nobody call positronium a quasiparticle?
The original quasi-particle is the phonon.
Ultimately, it comes down to convenience. It's a zoo down there. Physicists have to impose some order to be able to say anything about what goes on.
The positronium is a bound state of two real particles.
The crucial point is that the electrons at the top of a valence band have effective negative mass, i.e. they move opposite to an applied force. Of course their true mass hasn't changed, this is simply a consequence of the fact that we're considering a system of uncountably many electrons moving in unison. This means a full band carries no current (which is the situation in isolators), but if a band has some electrons missing at the top, these holes will be transported in the opposite direction of the usual electron current, which happens to be the correct direction for positive charges. Hence, we can talk about positive charge carries.
A better analogy would be a bubble of air underwater in a river. It moves with the flow of the water, not against it. I know it doesn't really matter, but I feel an analogy must at least have a core of truth.
Loved reading your first line’s first phrase as the sentence “I know all analogies.”
But yeah, this one was fun and I read it like you did at first as well!
Au contraire.
Analogies, mental models, metaphors help us make predictions. Better is better.
"The difference between the almost right word and the right word is really a large matter. 'tis the difference between the lightning bug and the lightning." ― Mark Twain
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2. abcd e
3. abc de
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Apart from theoretical considerations, we know it has to be like this because the voltage induced by the Hall effect flips for these kinds of semiconductors, and since there are no positively charged free particles in solids, this has to mean the electrons are now moving in the other direction, giving a complete illusion of a positive charge carrier.
Easier to study because electronics notation accidentally settled upon the arrow going from + to - instead of the direction electrons move, or easier for a deeper physical reason?
The authors studied simulations of electrical conduction in a semi-conductor crystal. They found "bound states" of two electrons with two holes, which they call "pi-tons" a kind of quasi-particle that only exists in the crystal. They hope to find experimental evidence for this.
This looks like a more complicated version of a one electron one hole bound state called an "exciton" [1].
(I have no expertise in this topic.)
(I always found it fishy they were called electromagnetic, photons alone have no charge, only when they actually hit something does the field appear.)
That would mean during Compton scattering experiment, electric field would show discrepancy due to spontaneous formation of excitons and/or pi-tons, especially if you used coherent standing wave beams of electrons and photons and vary the phases.
No. This discovery doesn't change how electromagnetism works.
This is a discovery a layer above electromagnetism. Quasi particles are a useful model, because you can use them more easily to explain stuff than through the fundamental forces. For example phonons (another quasi particle found in solid stat physics) explain heat transfer more easily than if you tried to solve all the wave equations from scratch.
(I like to think of quasi particles as analogous to chairs, desks and other every-day objects: they don't follow separate laws of physics, so nothing fundamentally new, but talking about them instead of just wave functions of electrons and nuclei has a much greater explanatory power).
Being the particles that mediate the electromagnetic force, they don't have charge themselves, but they only interact with particles that have charges. Think of it this way: When you have a charged particle, it will produce an electric field. And when you have a moving charged particle, it produces a magnetic field. Photons are how energy gets deposited into these fields. And by interacting with those photons, other particles can draw energy from this field.
Specifically, the sensors that use photoelectric effect do not react in the right wavelength, while standard radio sensors are also sensitive to charged particles. And presumably also use this exciton/pi-tons interface.
How can we exclude it? Presumably fire photons from putative EM field at neutrons, observe emitted photons with wavelength change? (Essentially Compton scattering experiment with neutral particles.)
My whole problem here is there's a lot of "seems as though" in those experiments... Like when you try to measure center of charge with it.
(Really, it's a little annoying that phys.org doesn't link to that directly -- a good proportion of physicists prefer to look at the arXiv version instead of the official published version even when they have access to the paywall!)
by Cleese, Idle, Palin, Jones (Posthumous) & al.