Lecture 13: Bose Condensates

More about Bose condensates. They're really weird -- at the lowest temperature, all bosons flock to the lowest available state, producing a "Bose condensate". Due to quantum mechanics, this is a remarkably stable state of matter, and is very hard to disturb. In fact, because the chemical potential becomes negative, it costs negative energy to add a new particle to the condensate. (Yes, bosons are "sticky" due to their statistics.) We also show why Bose condensates give rise to superfluidity (and superconductivity if the bosons are charged.) Class demonstration: The Wave (Just like the one in a baseball stadium.) The point is that many-body excitations often have very different character from the constituents. That is, "The Wave" in a crowd is an excitation of the crowd that doesn't look anything like the constituents (individual persons). Class discussions: What are superfluids and superconductors good for? What about the cuprate high temperature superconductors? Since they're ceramics, can you ever make them into wires? Are there higher temperature superconductors? How would room temperature superconductors make your life better? We also discuss the heat capacity of metals at the end of class. Some of the electrons in a metal are free to flow, and are in a fluid phase of matter that allows us to use the Fermi ideal gas to describe some of their behavior. Lecture Audio