The video discusses the concept of quasiparticles, which are particles that arise from the collective behavior of a system, in this case, semiconductors and transistors. The video starts by explaining how a device works by using the movement of electrons and positively charged holes in a circuit of diodes and transistors. The video then introduces the concept of quasiparticles, which are a class of strange emergent behaviors of nature that enable our most important technologies and are behind some of the weirdest phenomena that we have ever encountered.
The video then delves into the specific quasiparticle - the electron hole - which is a positively charged particle that arises when an electron is excited from its energy level. The video uses the example of a diode, a simple semiconductor device, to explain how the electron hole moves in the opposite direction of the flow of electrons under a voltage.
The video then introduces another type of quasiparticle, the phonon, which is a quantum of vibrational energy moving around the lattice of a crystal. The video explains how phonons behave in many ways like light, for example, they travel at the speed of their wave-type, have energy equal to the planck constant times their frequency, and can stack multiple phonons on top of each other in a single vibration.
The video then discusses how phonons are responsible for superconductivity, where the electrical resistance becomes zero when a metal is cooled near absolute zero. The video explains how the phonons take on a quasi-force that can bind electrons together, enabling electrons to stream through the lattice with zero resistance.
The video concludes by discussing how quasiparticles can build into complex hierarchies, just like regular particles, and that there are no doubt many more waiting to be discovered. The video ends by thanking Magellan TV for supporting PBS and promoting their streaming service.
1. The device being discussed here is a device with a circuit of diodes and transistors.
2. The device works due to the flow of electrons, which are negatively charged.
3. The device also works due to the movement of a class of strange emergent behaviors called quasi-particles.
4. Quasi-particles enable our most important technologies and are behind some of the weirdest phenomena encountered.
5. The discussion is about a particular quasiparticle that lets us talk about quasiparticles.
6. In semiconductors, the pushing around of a quasiparticle is equally important as the pushing around of electrons.
7. The central material to all modern electronics is silicon.
8. The silicon atom has 4 electrons in its outer or valence shell.
9. Atoms are most stable with full valence shells, which means 8 electrons.
10. Silicon likes to form covalent bonds with 4 other silicons, forming a tetrahedral crystal lattice.
11. These electrons are locked in place in the now-full valence energy level.
12. But they can still get bumped up to a higher energy state.
13. The first quasiparticle is an electron hole, which has an effective positive charge and an effective positive mass.
14. The simplest semiconductor device is the diode, which allows current to travel in one direction but not the other.
15. Diodes consist of two layers of silicon, one side with an excess of valence electrons and the other with a deficit.
16. This excess and deficit are achieved by doping - contaminating each layer by a different element.
17. Phosphorus is a popular choice for doping the silicon lattice with a tiny number of atoms that have 5 rather than 4 valence electrons.
18. The other side is doped with atoms that have 3 valence electrons - frequently boron.
19. At the p-n junction, extra electrons in the n-type diffuse into the gaps in the p-type, so we end up with a region where all valence shells are filled so charge can’t flow.
20. Apply a voltage in one direction and the holes and electrons flow away from this junction, expanding the non-conductive region and shutting down the current.
21. But apply the voltage the other way and the electrons and holes are driven towards the junction, causing it to narrow and electrons hop across, enabling the flow of electricity.
22. These p-n junctions also drive solar cells, LEDs, and transistors.
23. They all depend on the behavior of these quasiparticles - these holes.
24. Quasiparticles are emergent from the behavior of a particular configuration of matter.
25. Quasiparticles make it much easier to model physical processes like semiconductor junctions and in other cases they are indispensable.
26. Another quasiparticle is the phonon, a quantum of vibrational energy moving around the lattice.
27. Phonons behave in many ways like light.
28. They travel at the speed of their wave-type - sound in this case.
29. They have energy equal to the planck constant times their frequency.
30. They are boson-like in that you can stack multiple phonons on top of each other in a single vibration.
31. Phonons are also the quantum of heat.
32. Understanding the behavior of phonons is critical for the understanding of the behavior of both sound and heat in solids at the quantum scale.
33. Phonons are also really important for your computer, which, as you know, can get hot.
34. Energy is often transferred between phonons and other particles - quasi- and real - and modeling this is needed for modeling the behavior of heat on the quantum scale.
35. Electrons traveling through a circuit encounter resistance - they have collisions, which can be electromagnetic interactions with other electrons, falling into a hole, etc.
36. In doing so they can dump its energy into a vibrational mode and create a phonon.
37. This manifests as heat.
38. The heat due to electrical resistance is one of the main limitations on running your computer as fast as you might like to.
39. But quasiparticles can help there too.
40. We now have two types of quasiparticle -