I was just wondering if I have the right idea about whats going on in these quantum 'levitation' videos. So the little discs that zoom around on the track are made up of YBCO film on a super thin sapphire disc. YBCO is a superconductor and so it experiences the Meissner effect, that is that it produces a current within the material to oppose the magnetic field thus essentially expelling it. While it experiences this it is important to remember that YBCO is a type two superconductor so it has thin quantums of flux passing through it (fluxoids). These are areas in which the YBCO has lost its superconducting ability and so its ability to expel a magnetic field. It's these flux tubes which cause the material to become locked in the magnetic field. Due to the Meissner effect the superconductor will create a current to counter the flux in the flux tubes. Once this has happened the material is essentially locked in place as any attempt to move it will result in an opposing force from the superconductor. It is this phenomenon which allows the YBCO to locked in any position i.e tilted, upside-down etc. My question (aside from do I have the right idea of whats going on) is, what exactly is the role of the sapphire? Is it the sapphire or the YBCO that causes the flux tubes? I've read conflicting reports about which one causes it.